Christian
COURTOIS

Fonctions actuelles

Dans le laboratoire

• 10 juin 2022 :

  Directeur du CERAMATHS

1. Yeskendir, B., Dacquin, J.-P., Lorgouilloux, Y., Courtois, C., Royer, S., Dhainaut, J.

From metal-organic framework powders to shaped solids: Recent developments and challenges (2021) Materials Advances, 2 (22), pp. 7139-7186. 

Abstract

Metal-organic frameworks represent a class of porous materials which have developed considerably over the past few years. Their highly porous structure makes them outperform conventional adsorbents in hot topics such as dihydrogen and methane storage, and carbon dioxide capture. Their consequent modularity, based on the assembly of organic linkers and metal ions or clusters, also brings novel perspectives in catalysis, sensing and drug delivery just to name a few. However, one of the main bottlenecks to their broader use remains their shaping. Especially, shaped materials should present long-term mechanical stability as well as preserve their physical and chemical properties. This makes shaping of MOFs a special case as their thermal and chemical stabilities remain a downside as compared to other traditional porous materials such as silicas and zeolites today. Therefore, ever-increasing efforts have been devoted to the shaping of these materials. In this review, the state of the art for the preparation of shaped 3D MOF-based materials will be presented. Emphasis will be given to the final physical and chemical properties of the shaped solids comparatively to the initial powders, when data are available. In the first part, traditional techniques based on applying a significant force to MOF-based powders will be reviewed. These include pelletization, granulation, and extrusion, which generally lead to an increase of the final volumetric gas uptake of the objects. At the same time, the advantages and disadvantages of each technique will be discussed as well as the main outcome on the final objects. In the second part, the focus will be on newly-emerging techniques such as 3D printing and spray drying. The former also maximizes the volumetric gas uptake of the final materials, and for both techniques the quality of the final objects heavily relies on the working parameters. Finally, the third part will include the so-called "phase separation"shaping techniques which are for the most part performed without using special techniques. This implies shaping via physical and chemical phenomena such as sublimation and precipitation. Subsequently, a discussion on the performance of these materials for adsorption-based applications will be provided. Finally, perspectives and future outlook will be discussed. © The Royal Society of Chemistry.

1. Renaux, M., Méresse, D., Pellé, J., Thuault, A., Morin, C., Nivot, C., Courtois, C.

Mechanical modelling of microwave sintering and experimental validation on an alumina powder (2021) Journal of the European Ceramic Society, 41 (13), pp. 6617-6625. 

Abstract

Microwave sintering (MW) allows fast heating (≤30 min) and densification of ceramic materials, like alumina Al2O3. In order to predict the final material properties (density, size and grain size) the mechanical SOVS (Skorohold Olevsky Viscous Sintering) model is adapted and validated for conventional sintering of alumina. The model is implemented on ABAQUS with UMAT subroutine. Secondly, the SOVS model is modified for the microwave sintering by adapting the shear viscosity Arrhenius type law. Pre-exponential and exponential coefficients are modified for MW sintering. The calculated relative densities are compared to experimental results from conventional and microwave sintering and the relative difference remains under 3%. The coefficients identified for the MW sintering reveal a decrease in the shear viscosity by around 10 and an increase by up to 50 times in the grain boundaries diffusion coefficient. © 2021

Author Keywords

Alumina;  Densification;  Mechanical SOVS model;  Microwave; Sintering

7) Jean, F., Courtois, C.

The PZT system

(2021) Encyclopedia of Materials: Technical Ceramics and Glasses, 3-3, pp. 345-357. 

8) Chelli, Z., Achour, H., Saidi, M., Laghrouche, M., Chaouchi, A., Rguiti, M., Lorgouilloux, Y., Courtois, C.

Fabrication and characterization of PU/NKLNT/CFs based lead-free piezoelectric composite for energy harvesting application (2021) Polymer-Plastics Technology and Materials, 60 (12), pp. 1344-1356. 

Abstract

For vibration energy harvesting applications, a flexible composite material based on a polyurethane (PU) polymer matrix filled with polycrystalline particles (Na0.535K0.48)0.966 Li0.058 Nb0.9Ta0.1O3 (NKLNT) and crushed carbon fibers (CFs) has been developed by tape-casting method. NKLNT was synthesized by the solid-state route. The powder mixture of NKLNT and CFs was dispersed in the solution obtained by dissolving polyurethane in Cyclohexane. A maximum electrical power has been obtained for 0.5 wt.% at an electrical resistance of 5.105 Ω, which allows us to supply low-power electronic systems. A high piezoelectric charge coefficient (d33 = 147pC.N−1) of NKLNT indicates its potential application in flexible energy harvesting. © 2021 Taylor & Francis.

Author Keywords

composite material;  Energy harvesting;  pu/NKLNT/CFs composite;  solid route; tape-casting

9) Kennour, S., Lamrani-Amaouz, N., Chaouchi, A., Rguiti, M., Lorgoilloux, Y., Courtois, C.

Impedance spectroscopy analysis and piezoelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 + 0.3wt.% Sm2O3 lead-free ceramics sintered at different conditions

(2020) Ferroelectrics, 568 (1), pp. 5-22. 

Abstract

(Na0.5Bi0.5)0.94Ba0.06TiO3 + 0.3 wt.% Sm2O3 (named NBT-BT) lead-free piezoelectric ceramics were prepared by normal sintering. The effect of atmosphere sintering on NBT-BT ceramics was investigated through X-ray diffraction, dielectric, ferroelectric and piezoelectric characterizations. Real (Z′) and imaginary (Z″) parts of the complex impedance of the materials were also investigated. Dielectric studies exhibit a diffuse transition phase and are characterized by a temperature and frequency dispersion of permittivity, and this relaxation has been modeled using the modified Curie–Weiss law. The variation of the imaginary part (Z″) of impedance with frequency at various temperatures shows that the Z″ values reach a maxima peak (Z″max). The appearance of single semicircle in the Nyquist plots (Z″ vs Z′) pattern at high temperatures suggests that the electrical process occurring in the material has a relaxation process possibly due to the contribution of bulk material only. It shows that the compound exhibit negative temperature coefficient of resistance (NTCR) type behavior usually found in semiconductors. The bulk resistance of the material decreases with rising temperatures similar to a semiconductor, and the Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of materials. Also, the frequency-dependent AC conductivity at different temperatures indicated that the conduction process is thermally activated process. The plots of the relaxation times τZ″ and τM″ as a function of temperature follow the Arrhenius law, where a single slope is observed with activation energy values come to near 1.70. © 2020 Taylor & Francis Group, LLC.

Author Keywords

(Na0.5Bi0.5)0.94Ba0.06TiO3;  conductivity; dielectric relaxation;  impedance spectroscopy;  piezoelectric proprieties

10) Ndao, S., Duquennoy, M., Courtois, C., Ouaftouh, M., Rguiti, M., Smagin, N., Rivart, F., Gonon, M., Martic, G., Pélegris, C., Jenot, F.

Development of ultrasonic surface acoustic wave humidity sensors [Développement de capteurs d'humidité ultrasonores à ondes acoustiques de surface]

(2020) Instrumentation Mesure Metrologie, 19 (3), pp. 205-210. 

Abstract

In a European project called CUBISM, humidity sensors based on IDT (Inter Digital Transducer) technology are developed for the generation and detection of surface acoustic waves (SAW). These sensors are designed to operate at high temperature (500°C) for monitoring the drying of refractory concrete. Indeed, this humidity monitoring is important because a sudden evaporation of the water during the achievement of the structure could lead to high pressures in the pores implying consequently the destruction of the structure. Thus, the optimization of the concrete drying cycle must be combined with relevant in-situ physical measurements (humidity, pressure, temperature) and thermomechanical modelling. The real-time availability of this physical data via specific sensors integrated into the concrete is therefore a key to effective drying monitoring. Thus, for this project and its specific constraints, we have chosen the development of SAW humidity sensors because they are the most suitable to meet the specifications. In this study, the optimized parameters include the nature of the humidity-sensitive layer, the nature of the piezoelectric substrate, the architecture of the electrode array and finally the electronic measurement setup. © 2020 Lavoisier. All rights reserved.

Author Keywords

Humidity sensor;  Interdigital sensor;  SAW sensor; Surface acoustic wave;  Ultrasonic sensor

1. Stekke, J., Tendero, C., Tierce, P., Courtois, C., Rauwel, G., Lo, J., Guillot, P., Pigache, F.

Low-voltage plasma jet with piezoelectric generator: Preliminary evaluation of decontamination capabilities (2020) IEEE Transactions on Plasma Science, 48 (5), art. no. 9075986, pp. 1264-1270. 

Abstract

This article deals with the proof of concept and the preliminary evaluation of decontamination performances obtained with a plasma jet generated by a piezoelectric transformer (PT). This low-voltage supply solution (<10 V) is investigated as a plasma jet device, compact and safe solution for the decontamination of medical thermo-sensitive devices. The principle of the piezoelectric generator is presented, followed by the optical s-protocol conditions for the bactericidal effect observations, and finally the reduction rates obtained on Pseudomonas aeruginosa and Staphylococcus aureus bacteria strains with an argon plasma jet at atmospheric pressure about 2.5-W electrical input power. © 1973-2012 IEEE.

Author Keywords

Atmospheric plasma jet;  decontamination;  piezoelectric transformer (PT)

1. Orlik, K., Lorgouilloux, Y., Marchet, P., Thuault, A., Jean, F., Rguiti, M., Courtois, C.

Influence of microwave sintering on electrical properties of BCTZ lead free piezoelectric ceramics (2020) Journal of the European Ceramic Society, 40 (4), pp. 1212-1216. 

Abstract

Barium titanate doped with calcium and zirconium (BCTZ) could be used at low temperature to replace lead based piezoelectric ceramics (PZT). The classical way to obtain BCTZ is the solid-state route coupled with conventional sintering, but this step is time-consuming. To reduce the duration of this process, microwave heating was used for sintering. It is a fast sintering method and the heating rate was around 200 °C/min in this study. Slightly better electrical properties with finer microstructures (d33* = 706 pm/V, grain size about 42.1 ± 14.2 μm) were obtained for samples sintered by microwave heating during 50 min compared to the conventional sintering (d33* = 622 pm/V, 22.6 ± 4.4 μm). The main result of this study is that by using microwave heating, the sintering step duration (including heating, dwell time and cooling) was drastically reduced: 1.5 h for microwave sintering against 12.5 h for conventional sintering. © 2019 Elsevier Ltd

Author Keywords

BCTZ;  Ferroelectric properties;  Lead-free piezoceramics;  Microwave sintering;  Piezoelectric properties

13) Trelcat, J.-F., Basile, N., Gonon, M., Rguiti, M., Courtois, C., Leriche, A.

Sintering of BaTiO3 powder/sol composite thick films and their dielectric and piezoelectric properties (2020) Journal of Sol-Gel Science and Technology, 93 (3), pp. 657-665. 

Abstract

In this work, barium titanate thick films are produced at low-temperature using a modified sol–gel/ceramic powder technology named the composite route. In this process, a commercial BaTiO3 powder, doped or not by Li2O as sintering aid, is mixed with a stabilized titanium (IV) isopropoxide/barium acetate sol to obtain a composite ink. Two sols, using different solvents and chelating agents, are tested. Characterization of the evolution of theses sols with an increase in temperature is realized by thermal analyses (TGA and DTA) and X-ray diffraction. The four type of inks obtained are screen-printed on metallized alumina substrates and sintered. Microstructures and electrical properties of the sintered composite films are compared to those processed from a conventional ink obtained by dispersing the barium titanate powder in an organic vehicle. Measurements of dielectric/piezoelectric properties highlight higher charge coefficients d33 for composite thick films (69 vs. 45 pC/N for conventional thick films at close thickness values) despite a lower relative permittivity (340 vs. 658) certainly due to the presence of a single domain BaTiO3 nano-crystallites. [Figure not available: see fulltext.]. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Author Keywords

BaTiO3;  Composite inks;  Dielectric and piezoelectric properties;  Li2O sintering aid;  Sol–gel; Thick films

14) Zidi, N., Chaouchi, A., Rguiti, M., Lorgouilloux, Y., Courtois, C.

Dielectric, ferroelectric, piezoelectric properties, and impedance spectroscopy of (Ba0.85Ca0.15)(Ti0.9 Zr0.1)O3-x% (K0.5Bi0.5)TiO3 lead-free ceramics

(2019) Ferroelectrics, 551 (1), pp. 152-177. 

Abstract

The influence of (K0.5Bi0.5)TiO3 on structure, microstructure and piezoelectric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) piezoelectric ceramics was investigated. Impedance spectroscopy was used to get better understanding of the electrical properties of the materials as a function of temperature and frequency. The XRD results indicate the presence of the morphotropic phase in the BCTZ–xKBT system. Dielectric and complex impedance spectroscopic studies were carried out over wide frequency (i.e. 102–106 Hz) and temperature (30–500 °C) ranges. The diffuseness of the dielectric peak was found to increase with increasing KBT proportion. The nature of frequency dependence of AC conductivity of BCTZ-KBT follows the Jonscher power law and calculated DC conductivity follows Arrhenius behavior. The Nyquist plots suggest the contribution of grains and grain boundaries to the electrical behavior of the materials. The ceramic with x = 0.25 mol% KBT demonstrates good properties: d33 = 226 PC/N, Tc = 110 °C, kp = 27.85%, εr =10,566, tanδ = 2.3%. © 2019, © 2019 Taylor & Francis Group, LLC.

Author Keywords

(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3;  (Bi0.5K0.5)TiO3;  AC impedance; dielectric properties;  electric properties;  lead-free piezo-ceramics;  low sintering temperature

15) Ndao, S., Duquennoy, M., Courtois, C., Ouaftouh, M., Rguiti, M., Smagin, N.

Sensitivity range optimization of surface acoustic wave humidity ultrasonic sensors incorporating a polyvinyl alcohol (PVA) layer (2019) Proceedings of IEEE Sensors, 2019-October, art. no. 8956596, . 

Abstract

In this paper, Surface Acoustic Wave (SAW) delay line (DL) based humidity sensors are optimized. These sensors comprise two ultrasonic interdigital transducers (IDT) for generating and detecting SAW. The SAWs propagate along a piezoelectric substrate covered with a polyvinyl alcohol (PVA) layer that is sensitive to humidity. PVA layers are conventionally used in capacitive, resistive or acoustic resonance humidity sensors because of their sensitivity to humidity and low fabrication cost. The PVA layers are generally prepared with 10 wt% and their sensitivity range is from 10% to 90% relative humidity (RH) at room temperature. However, some applications require sensors capable of measuring RH greater than 90%. Therefore, in this study, several PVA layers with different mass percentages were considered to optimize and increase the sensitivity range of these ultrasonic sensors. It is shown that a 5 wt% PVA layer has a sensitivity range from 10% to 98% RH with good repeatability, as well as hysteresis of less than 0.5%. Finally, the mechanisms underlying the response of SAW humidity sensors are also discussed and analyzed. © 2019 IEEE.

Author Keywords

humidity sensor;  hygroscopic PVA layer;  IDT sensor; SAW sensor

16) Ferri, A., Rault, F., Da Costa, A., Cochrane, C., Boudriaux, M., Lemort, G., Campagne, C., Devaux, E., Courtois, C., Desfeux, R.

Local Electrical Characterization of PVDF Textile Filament (2019) Fibers and Polymers, 20 (7), pp. 1333-1339. 

Abstract

The piezoelectric behavior of poly(vinylidene fluoride), PVDF, has been known for several decades and is clearly related to its crystalline phases. Many works made on films or fibers have focused on the characterization of the phase transitions during various PVDF processing and on its electromechanical activity by combining several techniques. Piezo-force microscopy (PFM) is an interesting tool to underline the crystalline forms and piezoelectricity efficiency of PVDF at the local scale. However, this technique is little used on samples in the form of fibers and in this case, it is most often nanofibers. In this work, two conventional PVDF textile filaments, with different weak draw ratio, are produced and analyzed by FTIR, XRD, and PFM. We demonstrate that the PFM analysis can be relevant for specimens presenting low signals during other characterizations. Therefore, the local piezo-/ferroelectricity into the fiber is highlighted underlining the existence of the polar phases of PVDF. Then, the effective piezoelectric coefficient d33 of PVDF fiber drawn with a ratio of 1.5 is estimated at 12 pm/V. © 2019, The Korean Fiber Society.

Author Keywords

Melt-spun textile fiber; Piezo-force microscopy; Piezoelectric effect; Poly(vinylidene fluoride) PVDF

1. Ennawaoui, C., Lifi, H., Hajjaji, A., Samuel, C., Rguiti, M., Touhtouh, S., Azim, A., Courtois, C.

Dielectric and mechanical optimization properties of porous poly(ethylene-co-vinyl acetate) copolymer films for pseudo-piezoelectric effect (2019) Polymer Engineering and Science, 59 (7), pp. 1455-1461. 

Abstract

In this article, the authors present a porous copolymer film with pseudo-piezoelectric effects as a new candidate material for sensing applications. Porous films of poly(ethylene-co-vinyl acetate) (EVA) with a thicknesses ranging from 160 to 310 μm are fabricated by a coextrusion chemical foaming process and charged using a high-voltage contact charging process. Output performances (piezoelectric constant and relative permittivity) with related thermal/mechanical stability are specifically studied as a function of the film porosity and of the electrical charging process. The piezoelectric constant d33 increases with the cell porosity and an interesting piezoelectric constant close to 5.1 pC/N is achieved with a porous EVA film containing 65% of porosity. Actual results are then discussed using a theoretical solid–gas multilayer model to describe and predict the pseudo-piezoelectric effect of porous polymer materials. The originality of this work lies in the fact that all the steps leading to optimize pseudo piezoelectric films are included, and also in the use of EVA which is not a standard piezoelectric material. Therefore, this work is a contribution in the development of low-cost piezoelectric materials with potential applications as sensor in different fields such as medical, security, environment, sport, and transport. POLYM. ENG. SCI., 59:1455–1461 2019. © 2019 Society of Plastics Engineers. © 2019 Society of Plastics Engineers

1. Eddiai, A., Meddad, M., Rguiti, M., Chérif, A., Courtois, C.

Design and construction of a multifunction piezoelectric transformer (2019) Journal of the Australian Ceramic Society, 55 (1), pp. 19-24. 

Abstract

In recent years, piezoelectric materials have particularly found advantageous field of application in electrical energy’s conversion. Especially, the piezoelectric transformers are becoming more and more usable in electrical devices owing to several advantages such as small size, high efficiency, no electromagnetic noise, and non-flammability. The purpose of this study was to investigate a transformer design that allows having multi-functionality with different efficiency and wider range of voltage gain at resonance frequency. The piezoelectric transformer construction utilizes radial mode both at the input and output port and has the unidirectional polarization in the ceramics. An electromechanical equivalent circuit model based on Mason’s equivalent circuit was developed so as to describe the characteristics of the piezoelectric transformer. Excellent matching was found between the simulation data and experimental results. Finally, the results of this study will allow to deterministically designing multifunction piezoelectric transformers with specified performance. © 2018, Australian Ceramic Society.

Author Keywords

Efficiency; Multifunction;  Piezoelectric transformer;  Radial mode;  Voltage gain

19) Zidi, N., Chaouchi, A., Rguiti, M., Courtois, C., Lorgouilloux, Y.

Effect of CuBi2O4 additive on dielectric, ferroelectric, and piezoelectric properties of BCTZ lead free ceramics sintered at low temperature (2019) Proceedings - International Conference on Communications and Electrical Engineering, ICCEE 2018, art. no. 8634536, . 

Abstract

The influence of CuBi2O4 addition on sintering temperature, structural, dielectric and piezoelectric properties of (Ba, Ca)(Ti, Zr)O3 BCTZ ceramics prepared by the direct solid-state reaction were investigated. The X ray diffraction (XRD) data showed a single phase perovskite structure with morphotropic phase for all samples. The scanning electron microscopy observation showed the formation of glass phase in BCTZ doped compositions, which explain the reducing in sintering temperatures. The CuBi2O4 addition decrease the rhomboedral-Tetragonal transition temperature and slightly increase Curie temperature. Ferroelectric measurements show that remanent polarisation (P r), and the coercive field of ceramics firstly increases and then decreases with further increasing the CuBi2O4 content. The dielectric behavior of all samples exhibited diffuse phase transition behaviour. Samples of the BCTZ ceramics modified with 0.08% of CuBi2O4 exhibited the highest density (5.39 g/cm3), the highest dielectric constant (ϵr=10566.) and the best piezoelectric constant (d33 = 320 pC/N) © 2018 IEEE.

Author Keywords

(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3;  CuBi2O4; dielectric properties.;  lead-free ceramics;  low sintering temperature

20) Farhan, R., Rguiti, M., Eddiai, A., Mazroui, M., Meddad, M., Courtois, C.

Evaluation of performance of polyamide/lead zirconate titanate composite for energy harvesters and actuators (2019) Journal of Composite Materials, 53 (3), pp. 345-352. 

Abstract

By means of experimental tools, we have studied the effect of lead zirconate titanate volume fraction introduced in polyamide-6/lead zirconate titanate composites on dielectric, piezoelectric, mechanical, and structural properties. As the first result, we found that the insertion of lead zirconate titanate particles makes the dielectric permittivity of the polyamide-6 matrix increases from 10 to 95.8. The dielectric property studies reveal that under an electrical field of 1 kV the remnant polarization is also increased from 0.17 to 0.4, this behavior is related to both the increase of volume fraction of lead zirconate titanate from 20% to 40% and the piezoelectric coefficient changes proportionally with that of volume fraction of lead zirconate titanate. Furthermore, piezoelectric activity increases with lead zirconate titanate particle size at a range where there is a lower order of magnitude. Finally, the uniform dispersion of the ceramic lead zirconate titanate particles in polyamide matrix has been confirmed by scanning electron microscopy analysis. The performances reached by polyamide-6/lead zirconate titanate composites open new horizons for energy harvesting and actuators. © The Author(s) 2018.

Author Keywords

actuator;  energy harvesting;  lead zirconate titanate;  piezoelectric properties;  Polyamide-6

21) Dubois, A., Dubar, M., Debras, C., Hermange, K., Nivot, C., Courtois, C.

New environmentally friendly coatings for hot forging tools (2018) Surface and Coatings Technology, 344, pp. 342-352. 

Abstract

Two alumina coatings are developed to protect tool surface in hot forging: pure γ-alumina matrix loaded with α-alumina particles and pure γ-alumina matrix loaded with h-BN particles. The coatings are deposited on stainless tools by using a sol-gel procedure. Adherent coatings are obtained with an average thickness ranging from 200 to 300 nm. The coatings are tested according to the conditions of contact encountered in hot forging processes: coated tools slide against the surface of hot specimens where they generate a plastic strain. The design of experiment involves specimens heated to 1100 °C, lubricated and unlubricated contact, small and large specimen plastic strain, uncoated and sol-gel coated tools. Tests results are the Coulomb's coefficient of friction, SEM-EDS and roughness measurement of the tool surfaces after a sliding length of 40 mm. Results show that the tested sol-gel coatings remain firmly bonded to the tool surface. Compared to uncoated tools, alumina sol-gel coatings limit the amount of material transfer from specimen surface to tool surface. Loading the alumina sol-gel coating with h-BN particles significantly improves its friction behaviour: the friction coefficient is lower and sticking phenomena are reduced. © 2018 Elsevier B.V.

Author Keywords

Friction; h-BN;  Hot forging;  Sol-gel coating;  Wear;  α-alumina

22) Takpara, R., Duquennoy, M., Ouaftouh, M., Courtois, C., Jenot, F., Rguiti, M.

Optimization of SAW-type Surface Wave Ultrasonic Sensors for Ultrasonic SHM (2018) Research in Nondestructive Evaluation, 29 (2), pp. 61-77. 

Abstract

Surface acoustic waves (SAW) are particularly suited for effectively monitoring and characterizing a structure’s surfaces (condition of the surface, coating, thin layer, micro-cracks, etc.), and in some cases it is necessary to permanently keep the sensors on the structures to enable continuous monitoring. This article focuses on the optimization of SAW-type interdigital sensors (or IDT sensors for InterDigital Transducer) because they can largely address this issue. Initially, the ability of piezoelectric materials (lead zirconate titanate [PZT] and Niobate de lithium) to generate SAW is studied by modeling. Then a design of an IDT sensor is defined and optimized for the generation of SAW on a substrate. Parameters such as electrode’s periodicity, thickness of piezoelectric plate, and type of contact between the plate and the substrate, are studied. Finally, experimental results are compared with those obtained by modeling. © 2018 American Society for Nondestructive Testing.

Author Keywords

IDT sensor;  SAW sensor;  ultrasonic NDT;  ultrasonic SHM

23) Aboubakr, S., Hajjaji, A., Rguiti, M., Benkhouja, K., Courtois, C., Boughaleb, Y.

Effect of fillers size on the dielectric and piezoelectric characteristics of a piezoelectric composite (2018) EPJ Applied Physics, 81 (2), art. no. 20901, . 

Abstract

Recent trends in electromechanical conversion using alternative materials, have demonstrated the advantages of using piezoelectric composites for energy generation. There have been several papers on ceramic/polymer composites in which the fillers have high piezoelectric constant. Basically, the energy harvested depends on the proportion of the piezoelectric properties of composite. The fillers size within the composites is also an important criterion of the composites properties. Thus, in this paper 0-3 composites, made of lead zirconate titanate (PZT) ceramic powder and polyurethane (PU) were prepared. Different sizes of ceramic grains were used: grains with average size of 10 μm, size under 80 μm and size under 100 μm. Sizes of the PZT grains was determined according to the homogenization efficiency of the composite. Piezoelectric (piezoelectric coefficient dinf33/inf) and dielectric properties

(dielectric constant) were investigated. They have shown an interesting improvement with the increasing grains size up to 20 pC/N and 100, respectively. In order to understand the composite behavior on the microscopic scale, a simulation was carried out by mean of a finite element method (FEM) software. Finally, an estimation of the harvested voltage was modeled according to the grains size. © EDP Sciences, 2018.

1. De Neef, A., Samuel, C., Stoclet, G., Rguiti, M., Courtois, C., Dubois, P., Soulestin, J., Raquez, J.-M.

Processing of PVDF-based electroactive/ferroelectric films: Importance of PMMA and cooling rate from the melt state on the crystallization of PVDF beta-crystals

(2018) Soft Matter, 14 (22), pp. 4591-4602. 

Abstract

Poly(vinylidene difluoride) (PVDF) displays attractive ferroelectric/piezoelectric properties and its polar β-crystals are specifically targeted for achieving electroactive applications. However, their direct crystallization from the melt state represents a challenging task that has never been addressed using meltstate processes. The use of poly(methyl methacrylate) (PMMA) is herein investigated to promote the PVDF polar β-phase using melt-blending and extrusion-calendering technologies. The presence of the β-phase is here confirmed by ATR-FTIR and WAXS experiments with blends at a PMMA content as low as 5 wt%. The key role of PMMA for the β-phase crystallization from the melt state was unambiguously highlighted with the help of Flash DSC experiments in non-isothermal cooling mode from the melt state. PMMA is able to efficiently shift the α-to-β crystal transition to lower cooling rates (&gt;100-200 °C s-1), making the achievement of the PVDF polar β-phase for these blends compatible with conventional processing tools. A crystal phase diagram is proposed for the PVDF/PMMA blends to highlight the dual effects of both PMMA and cooling rate on the PVDF crystallization during meltprocessing. Ferroelectric properties were even observed for the blends containing PMMA up to 10 wt% with the highest remanent polarization obtained at 5 wt% PMMA. After 10 wt% PMMA, a progressive transition from ferroelectric to pseudo-linear dielectric behavior is observed more likely due to the presence of PMMA in the interlamellar amorphous phase of the polar PVDF spherulites as shown by SAXS experiments. In this work, we successfully demonstrated that PMMA plays a key role in the crystallization of PVDF polar crystals from the melt state, enabling large-scale and continuous extrusion processing of PVDF-based materials with attractive dielectric properties for sensing and harvesting applications. © 2018 The Royal Society of Chemistry.

1. Takpara, R., Duquennoy, M., Ouaftouh, M., Courtois, C., Jenot, F., Rguiti, M.

Optimization of PZT ceramic IDT sensors for health monitoring of structures (2017) Ultrasonics, 79, pp. 96-104. 

Abstract

Surface acoustic waves (SAW) are particularly suited to effectively monitoring and characterizing structural surfaces (condition of the surface, coating, thin layer, micro-cracks…) as their energy is localized on the surface, within approximately one wavelength. Conventionally, in non-destructive testing, wedge sensors are used to the generation guided waves but they are especially suited to flat surfaces and sized for a given type material (angle of refraction). Additionally, these sensors are quite expensive so it is quite difficult to leave the sensors permanently on the structure for its health monitoring. Therefore we are considering in this study, another type of ultrasonic sensors, able to generate SAW. These sensors are interdigital sensors or IDT sensors for InterDigital Transducer. This paper focuses on optimization of IDT sensors for non-destructive structural testing by using PZT ceramics. The challenge was to optimize the dimensional parameters of the IDT sensors in order to efficiently generate surface waves. Acoustic tests then confirmed these parameters. © 2017

Author Keywords

IDT sensor;  SAW sensor;  ultrasonic NDT;  ultrasonic SHM

1. Aboubakr, S., Hajjaji, A., Rguiti, M., Benkhouja, K., Courtois, C.

A high dielectric composite for energy storage application

1. International Journal of Hydrogen Energy, 42 (30), pp. 19504-19511. 

Abstract

Piezoelectric composites are widely studied due to their good performances. Several kinds of these composites have been developed for sensing and actuation applications, however, most of them are not used for energy storage devices, because of their low dielectric properties. In this research work, a three-phase composite was developed. This latter was obtained by adding a small amount, up to 3%, of a (AL) to a piezoelectric composite. The Dielectric constant was found to be clearly increased with the increasing volume fraction of Aluminum. A comparison of piezo- and ferroelectric activities between different composites samples reveal a high improvement of the energy storage density, which reaches 11 J/cm2. In addition to that, it was found that the dielectric properties remain stable even at high temperature. For these reasons, this novel three-phase composite can be used for multifunctional embedded capacitors applications. © 2017 Hydrogen Energy Publications LLC

Author Keywords

Composite; Dielectric;  Efficiency;  Energy; Piezoelectric;  Storage

1. Aboubakr, S., Hajjaji, A., Benkhouja, K., Rguiti, M., Courtois, C.

Optimization and improvement of energy storage efficiency in a flexible dielectric capacitor

1. Proceedings of 2016 International Renewable and Sustainable Energy Conference, IRSEC 2016, art. no. 7983894, pp. 921-924. 

Abstract

Capacitors which are dedicated to microelectronic applications require a lot of characteristics. Indeed they should have a high capacitance but shaped in small sizes, moreover, for some specific applications those capacitors should be flexible to be easily integrated in circuits. A lot of materials are used for this purpose. But, in order to combine all this features, a composite made of three phases was developed. This material was obtained by adding a small amount, up to 3%, of Aluminum (AL) to the PZT/PU composite. A study about its characteristics wad conducted. It was found that the addition of the conductive fillers has clearly enhanced the dielectric behavior of the whole material. Moreover, the high dielectric constant achieved is about 110. This result led to an improvement of the energy that can be stored within this capacitor and which reached 11J/cm2. © 2016 IEEE.

Author Keywords

Composite; Density;  Dielectric;  Efficiency; Energy;  Storage

1. Champagne, P., Courtois, C., Leriche, A.

Development of protective and decontaminating coatings [Élaboration de revêtements protecteurs et dépolluants] (2017) Actualite Chimique, (420), pp. 35-36. 

1. Leveque, M., Douchain, C., Rguiti, M., Prashantha, K., Courtois, C., Lacrampe, M.-F., Krawczak, P.

Vibrational energy-harvesting performance of bio-sourced flexible polyamide 11/layered silicate nanocomposite films (2017) International Journal of Polymer Analysis and Characterization, 22 (1), pp. 72-82. 

Abstract

The energy-harvesting efficiency of melt processed polyamide 11 (PA11) films and its nanocomposites have been investigated as a function of filler type and content. In the present work, nanoclays have been used as structural modifiers in a PA11 matrix. The nanocomposites were prepared using layered clays, Cloisite 20A, 10A, and Na+, by extrusion process through varying the filler content, 1, 2, 4, and 5 wt.%. The crystalline structure of these nanocomposites has been studied by X-ray diffractometer. It has been demonstrated that layered silicates are not significant for the structural quality of the obtained nanocomposites. Regarding the interlayer peak of different clays, it has also been revealed that Cloisite 20A is partially exfoliated, whereas 10A and Na+ are totally exfoliated in the PA11 matrix. From mechanical and dynamic mechanical analyses, it was found that the addition of layered silicates results in an increase in mechanical properties. The piezoelectric strain coefficient d33 and dielectric constant εR have been measured on polarized films at ambient temperature. Among all the prepared nanocomposites only Cloisite Na+-loaded PA11 nanocomposites showed the best piezoelectric constant. This observation showed that piezoelectric constant not only depends on the crystalline phases but also on the nature of the filler. Cloisite Na+ is more polar than other modified clays and high polarity leads to a better polarization response. A specific method for the quantification of energy vibration recovery has been developed for these nanocomposites. The capabilities of vibrational energy recovery were studied on PA11 loaded with Cloisite Na+. © 2017, Copyright © Taylor & Francis Group, LLC.

Author Keywords

Energy harvesting; layered silicates;  piezoelectric;  polyamide 11

30) Senoussi, H., Osmani, H., Courtois, C., Bourahli, M.E.H.

Mineralogical and chemical characterization of DD3 kaolin from the east of Algeria (2016) Boletin de la Sociedad Espanola de Ceramica y Vidrio, 55 (3), pp. 121-126. 

Abstract

The mineralogical and chemical characteristics, based on X-ray diffraction (XRD) and scanning electron microscopy, of a kaolin known as DD3, from eastern Algeria were examined in the present study. The results showed that kaolin DD3 has an alumina content of 39%. The SiO2/Al2O3 molar ratio of 2.14 is close to that of a pure halloysite. The hematite concentration is relatively large and the flux oxides ratios remain as acceptable impurities.

Microscopic observations showed a predominant tubular halloysite phase, flattened hexagonal platelets corresponding to the presence of kaolinite and its polymorphs (nacrite, dickite), and hydrated alumina. The SiO2/Al2O3 molar ratio and tubular DD3 suggest possible uses in technical ceramics and nanotechnology applications. Analysis by XRD revealed the presence of many phases. Thermal treatment at 450 °C and chemical treatment with HCl confirmed the presence of halloysite. The inclusion in the clay of organic molecules (dimethylsulfoxide (DMSO), DMF, and diluted glycerol) showed that the DMSO led to expansion of the inter-planar distance. The intercalation by DMSO molecules resulted in a shift of the basal peak from 10 to 11.02 Å and partial displacement of the peak from 3.35 to 3.65 Å. These two peaks are characteristic of halloysite. The presence of residual nacrite was also confirmed by the shift of the peak observed at 3.35 Å. A full analysis of the XRD patterns using the Match software, based on these results, showed that the DD3 clay consists of &gt;60% halloysite. © 2015 SECV. Published by Elsevier Espana, S.L.U. This is an open access article under theCC BY-NC-ND license.

Author Keywords

Halloysite; Identification; Intercalation;  Kaolin;  Organic molecules intercalation

31) Boudriaux, M., Rault, F., Cochrane, C., Lemort, G., Campagne, C., Devaux, E., Courtois, C.

Crystalline forms of PVDF fiber filled with clay components along processing steps (2016) Journal of Applied Polymer Science, 133 (14), art. no. 43244, . 

Abstract

There is a growing interest in the supply of autonomous electronic devices, particularly in the field of smart textiles. Energy harvesting is considered as a clean and renewable alternative technology to reach this objective. One of the methods explored is scavenging the energy from ambient mechanical vibrations by using piezoelectric materials. Due to textile requirements, the development of PVDF based fibers appears to be an interesting solution. However, the amount of its β crystalline form should be as high as possible. PVDF/clay components (modified or unmodified clay as well as organic modifier) containing up to 5 wt % additive are prepared by melt spinning. FTIR and XRD experiments show that the most important factor for obtaining high levels of β crystalline form is to increase the drawing ratio. The results indicate also that an organic modifier (quaternary ammonium salt) influences the crystalline forms and leads to a high ratio of β phases. © 2015 Wiley Periodicals, Inc.

Author Keywords

clay; crystallization;  nanostructured polymers;  plasticizer;  X-ray

1. Touhtouh, S., Rguiti, M., Courtois, C., Belhora, F., Arbaoui, A., Dastorg, S., Rachek, A., Hajjaji, A.

PU/PZT composites for vibratory energy harvesting

1. Optical and Quantum Electronics, 48 (4), art. no. 246, . 

Abstract

Piezoelectric composites of PU/PZT with 0–3 connectivity were prepared in the film form. Homogeneous dispersion of the ceramic PZT in polyurethane matrix has been obtained and has been verified by SEM analysis. Dielectric properties reveal that under an electrical field of 1000 V the remnant polarization increased from 1.9 to 4 µC/cm−2 when the volume fraction of PZT increased from 50 to 80 %. Modeling and vibratory energy harvesting tests has been realized. At very low frequency and deformation, and without application of any static electric field, 1.15 µW of power has been obtained. The results obtained in this work contribute to demonstrate the ability of the incorporation of PZT particles in the polymer matrix to improve the conversion efficiency of the vibratory energy into electrical energy for the development of µ-generators. © 2016, Springer Science+Business Media New York.

Author Keywords

Composites; Films;  Piezoelectric properties;  Vibratory energy harvesting

1. Aboubakr, S., Rguiti, M., Yessari, M., Elballouti, A., Courtois, C., Hajjaji, A.

Dielectric characterization of lead zirconate-titane(PZT) /polyurethane(PU) thin film composite: Volume fraction, frequency and temperature dependence

1. Molecular Crystals and Liquid Crystals, 627 (1), pp. 82-91. 

Abstract

The Lead Zirconate-titane(PZT) ceramic is known by its piezoelectric characteristic, but also by its stiffness. The use of a composite based on a polyurethane (PU) matrix charged by a piezoelectric material, enable to generate a large deformation of the material, therefore harvesting more energy. This new material will provide a competitive alternative and low cost manufacturing technology of autonomous systems (smart clothes, car seat, boat sail, flag …). A thin film of the PZT/PU composite was prepared using up to 80 vol. % of ceramic. Due to the dielectric nature of the PZT,inclusions of this one in a PU matrix raise the permittivity of the composite. For the most of industrial applications, the composite will not be used at room temperature, and as the energy harvested from this new materials have a direct relation with their permittivity we have made a study about the variation of the permittivity at different temperature and frequencies. © 2016 Taylor & Francis Group, LLC.

Author Keywords

composite; dielectric;  Piezoelectric;  PU; PZT

1. Takpara, R., Duquennoy, M., Courtois, C., Gonon, M., Ouaftouh, M., Martic, G., Rguiti, M., Jenot, F., Seronveaux, L., Pelegris, C.

Development of flexible SAW sensors for non-destructive testing of structure (2016) AIP Conference Proceedings, 1706, art. no. 070003, . 

Abstract

In order to accurately examine structures surfaces, it is interesting to use surface SAW (Surface Acoustic Wave). Such waves are well suited for example to detect early emerging cracks or to test the quality of a coating. In addition, when coatings are thin or when emergent cracks are precocious, it is necessary to excite surface waves beyond 10MHz. Finally, when structures are not flat, it makes sense to have flexible or conformable sensors for their characterization. To address this problem, we propose to develop SAW type of interdigital sensors (or IDT for InterDigital Transducer), based on flexible piezoelectric plates. Initially, in order to optimize these sensors, we modeled the behavior of these sensors and identified the optimum characteristic sizes. In particular, the thickness of the piezoelectric plate and the width of the interdigital electrodes have been studied. Secondly, we made composites based on barium titanate foams in order to have flexible piezoelectric plates and to carry out thereafter sensors. Then, we studied several techniques in order to optimize the interdigitated electrodes deposition on this type of material. One of the difficulties concerns the fineness of these electrodes because the ratio between the length (typically several millimeters) and the width (a few tens of micrometers) of electrodes is very high. Finally, mechanical, electrical and acoustical characterizations of the sensors deposited on aluminum substrates were able to show the quality of our achievement. © 2016 AIP Publishing LLC.

1. Cherifi, Y., Chaouchi, A., Lorgoilloux, Y., Rguiti, M., Kadri, A., Courtois, C.

Electrical, dielectric and photocatalytic properties of Fe-doped ZnO nanomaterials synthesized by sol gel method (2016) Processing and Application of Ceramics, 10 (3), pp. 125-135. 

Abstract

Fe-doped ZnO nanoparticles were synthesized by sol gel technique. Fine-scale and single phase hexagonal wurtzite structure in all samples were confirmed by SEM and XRD, respectively. The band gap energy depends on the amount of Fe and was found to be in the range of 3.11-2.53 eV. The electric and dielectric properties were investigated using complex impedance spectroscopy. AC conductivity data were correlated with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (Rmin) and the density of states at Fermi level, N(EF). Fe doping in ZnO also improved the photocatalytic activity. Thus, the sample Zn0.95Fe0.05O showed high degradation potential towards methylene blue (MB), i.e. it degrades 90% of BM in 90min under UV light.

Author Keywords

Band Gap; Conductivity;  Dielectric Properties;  Fe-doped ZnO;  Photocatalytic Properties

36) Zidi, N., Chaouchi, A., D'astorg, S., Rguiti, M., Courtois, C.

Impedance spectroscopy studies on (Na0.5Bi0.5)0.94Ba0.06TiO3 + 0.3 wt% Sm2O3 + 0.25 wt% LiF lead-free piezoelectric ceramics (2015) Bulletin of Materials Science, 38 (3), pp. 731-737. 

Abstract

The a.c. complex impedance spectroscopy technique was used to obtain the electrical parameters of (Na0.5Bi0.5)0.94Ba0.06TiO3 +0.3 wt% Sm2O3 +0.25 wt% LiF lead-free ceramics in a wide frequency range at different temperatures. These samples were prepared by a high-temperature solid-state reaction technique and their single phase formation was confirmed by the X-ray diffraction technique. Dielectric studies exhibit a diffuse phase transition characterized by a temperature and frequency dispersion of permittivity, and this relaxation has been modelled using the modified Curie-Weiss law. The variation of imaginary part (Z″) of impedance with frequency at various temperatures shows that the Z″ values reach a maxima peak (Z″ max) above 400°C. The appearance of single semicircle in the Nyquist plots (Z″ vs. Z′) pattern at high temperatures suggests that the electrical process occurring in the material has a relaxation process possibly due to the contribution for bulk material only. The bulk resistance of the material decreases with rise in temperatures similar to that of a semiconductor, and the Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of these materials. The frequencies, thermal effect on a.c. conductivity and activation energy have been assessed. © Indian Academy of Sciences.

Author Keywords

(Na0.5Bi0.5)0.94Ba0.06TiO3;  Conductivity; Dielectric relaxation;  Impedance spectroscopy;  Low sintering

1. Saidi, M., Chaouchi, A., D’Astorg, S., Rguiti, M., Courtois, C.

Dielectric, ferroelectrics properties and impedance spectroscopy analysis of the [(Na0.535K0.480)0.966Li0.058] (Nb0.90Ta0.10)O3-based leadfree ceramics

(2015) Journal of Advanced Dielectrics, 5 (1), art. no. 1550007, . 

Abstract

Polycrystalline of [(Na0.535K0.480)0.966Li0.058] (Nb0.90Ta0.10)O3 samples were prepared using the high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis indicates the formation of a single-phase with orthorhombic structure. AC impedance plots were used as tool to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The AC impedance studies revealed the presence of grain effect, from 425°C onwards. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) characteristic of NKLNT. The AC conductivity results were used to correlate with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (Rmin), the density of states at Fermi level (N(Ef)), and the activation energy of the compound. © 2015 The Authors.

Author Keywords

AC impedance spectroscopy; Conductivity;  Dielectric properties;  Dielectric relaxation;  Lead-free piezo-ceramics

1. Pélegris, C., Ferguen, N., Leclerc, W., Lorgouilloux, Y., Hocquet, S., Rigo, O., Guessasma, M., Bellenger, E., Courtois, C., Lardot, V., Leriche, A.

Thermal conductivity modelling of alumina/Al functionally graded composites (2015) Canadian Journal of Chemical Engineering, 93 (2), pp. 192-200. 

Abstract

This paper describes a new manufacturing process for producing functionally graded ceramic-metal composites with anisotropic properties for thermal management in automotive engine blocks. These composites are elaborated by producing a porosity gradient within an alumina matrix, subsequently infiltrated by a molten aluminum alloy. The interconnected macro porosity inside the ceramic is controlled by the coalescence of PMMA

(PolyMethylMethAcrylate) spherical particles during the elaboration step of an organic frame template in which bridges are created at contact points between the particles. The diameter of the interconnection contact plays a key role because it greatly controls the microstructure of the final composites and consequently the thermal conductivity. A numerical model was developed for simulating the different steps of the elaboration process of the composites. Numerical assessments of the effective thermal conductivity are achieved in order to examine interconnection contact effects. To end up, the developed model is validated by comparing the numerical predictions with experimental measurements. © 2014 Canadian Society for Chemical Engineering.

Author Keywords

Ceramic-metal composite; Functionally graded material; Modelling;  Porosity gradient;  Thermal conductivity

39) Zidi, N., Chaouchi, A., D'Astorg, S., Rguiti, M., Courtois, C.

Dielectric and impedance spectroscopy characterizations of CuO added (Na0.5Bi0. 5)0.94Ba0.06TiO3 lead-free piezoelectric ceramics (2014) Journal of Alloys and Compounds, 590, pp. 557-564. 

Abstract

CuO was used to reduce the sintering temperature of (Na0 .5Bi0.5) 0.94-Ba0.06TiO3 + 0.03 wt.%Sm2O 3 (named NBTS) piezoelectric ceramics. Structural/micro-structural, dielectric, and resistive properties of this composition have been studied using impedance spectroscopic method to get better understanding of (i) the electrical conduction and dielectric relaxation mechanism and (ii) microstructure-electrical properties relationship of the materials as a function of temperature and frequency. The XRD patterns reveal the presence of the morphotropic phase MPB (coexistence of tetragonal and rhombohedral phase) for different compositions. Dielectric and complex impedance spectroscopic studies were carried out in a wide frequency (i.e., 102-106 Hz) and temperature (30-500 C) range. The maximum of permittivity (at transition temperature) was found to decrease with increasing CuO amount in NBTS, but the diffuseness of dielectric peak increases. The nature of frequency dependence of AC conductivity of NBTS follows the Jonscher power law, and calculated DC conductivity follows Arrhenius behavior. The Nyquist plots suggest that the grains only are responsible for the conduction mechanism of the materials. The occurrence of single arc in the complex modulus spectrum of NBTS compositions confirms the single-phase characteristics, and also confirms the presence of non-Debye type of multiple relaxation in the material. © 2013 Elsevier B.V. All rights reserved.

Author Keywords

(Bi0.5Na0.5)0.94Ba0.06TiO 3;  AC impedance spectroscopy;  Conductivity; Dielectric relaxation;  Lead-free piezo-ceramics;  Low sintering temperature

1. Haddad, H., Leclerc, W., Ferguen, N., Guessasma, M., Bellenger, E., Pélegris, C., Sciamanna, V., Maurye, N., Gonon, M., Takapara, R., Duquennoy, M.,Martic, G., Seronveaux, L., Courtois, C.

A discrete element method for composite material modeling (2014) Civil-Comp Proceedings, 106, . 

Abstract

The aim of the study, described in this paper, is to numerically identify the mechanical properties of composite materials using the discrete element method. This method provides an opportunity to treat the problems of discontinuity inducing damage and crack propagation. Initially, a qualitative and quantitative analysis is carried out for conventional tests (tensile, shear). The results are compared to those from using the finite element method. © Civil-Comp Press, 2014.

Author Keywords

Composite materials; Discrete element method;  Finite element method;  Mechanical properties

1. Saidi, M., Khalfaoui, K., Chaouchi, A., Dastorg, S., Rguiti, M., Courtois, C.

Ferroelectrics, piezoelectric, and impedance spectroscopy characterizations of CuO Doped (Na 0.52 K 0.44)(Nb 0.9 Sb 0.06)O 3 -0.04LiTaO 3 lead free ceramics

(2014) Ferroelectrics, 473 (1), pp. 171-186. 

Abstract

CuO was used to reduce the sintering temperature of (Na0.52 K0.44)(Nb0.9 Sb0.06)O3-0.04LiTaO3 (NKNSLT) piezoelectric ceramics. XRD analysis reveals the formation of single phase perovskite structure. SEM has been used to investigate the grain morphology of the material. Impedance plots have been used as a tool to analyze the electrical properties of the sample as a function of frequency and temperature. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 360°C, and exhibits diffuse phase transition. The Nyquist plot (Z′′ vs Z′′) revealed the presence only of the grain boundary effect in the materials. Bulk resistance is observed to decrease with an increase in temperature showing a typical negative temperature coefficient of resistance (NTCR). The plot of normalized complex dielectric modulus a function of frequency exhibits both short and long-range conduction in the ceramics. The ac conductivity spectrum was found to obey Jonscher's universal power law. © 2014 Taylor & Francis Group, LLC.

Author Keywords

(Na 0.52 K 0.44)(Nb 0.9 Sb 0.06)O 3

42) Kharchouche, F., Savary, E., Thuault, A., Marinel, S., DAstorg, S., Rguiti, M., Belkhiat, S., Courtois, C., Leriche, A.

Effects of microwave sintering on intrinsic defects concentrations in ZnO-based varistors (2014) Ceramics International, 40 (8 PART B), pp. 13697-13701. 

Abstract

Nowadays the most important part of varistors is made from doped ZnO. The typical varistor microstructure consists in a large number of n-p-n junctions. ZnO grains are intrinsic n-type semiconductors because of the displacement of zinc atoms in interstitial positions and the formation of oxygen vacancies. The addition of some dopants (for instance bismuth and antimony oxides) allows creating a p-type semiconduction at the grain boundaries. In our study, ZnO-based varistor with standard composition was sintered by microwave and in a conventional furnace with the same sintering temperatures and dwell times. Electrical characterizations after direct microwave sintering showed that these samples presented a high electrical conductivity which avoids getting a good current-voltage non-linearity. This high conductivity could be due to higher concentrations in interstitial zinc and oxygen vacancies after the microwave process. It is assumed that microwaves cause a displacement of the equilibria of those reactions leading to a partial reduction of the samples. A post thermal treatment in a conventional furnace at 650 °C for 24 h under oxygen atmosphere was realized so as to reach the thermodynamic equilibrium. After this treatment the electrical conductivity drastically decreased supporting the idea that the defects concentrations have also decreased. © 2014 Elsevier Ltd and Techna Group S.r.l.

Author Keywords

A. Microwave processing; C. Electrical properties;  D. ZnO;  E. Varistor

1. Aboubakr, S., Rguiti, M., Hajjaji, A., Eddiai, A., Courtois, C., D'Astorg, S.

Mechanical and dielectric characterization of lead zirconate titanate(PZT)/polyurethane(PU) thin film composite for energy harvesting (2014) Proceedings of SPIE - The International Society for Optical Engineering, 9059, art. no. 90590A, . 

Abstract

The Lead Zirconate titanate (PZT) ceramic is known by its piezoelectric feature, but also by its stiffness, the use of a composite based on a polyurethane (PU) matrix charged by a piezoelectric material, enable to generate a large deformation of the material, therefore harvesting more energy. This new material will provide a competitive alternative and low cost manufacturing technology of autonomous systems (smart clothes, car seat, boat sail, flag...). A thin film of the PZT/PU composite was prepared using up to 80 vol. % of ceramic. Due to the dielectric nature of the PZT, inclusions of this one in a PU matrix raises the permittivity of the composite, on other hand this latter seems to decline at high frequencies. © 2014 SPIE.

1. Dolay, A., Courtois, C., d'Astorg, S., Rguiti, M., Petitniot, J.-L., Leriche, A.

Fabrication and characterization of metal core piezoelectric fibres by dip coating process (2014) Journal of the European Ceramic Society, 34 (12), pp. 2951-2957. 

Abstract

Metal core piezoelectric fibres (MCPFs) show strong potential for structural actuator applications. Unfortunately the development of such fibres is problematic because of their fabrication difficulties. In order to obtain the best properties, both aspect ratio and piezoceramic-metal core compatibility have to be considered. For those reasons, fabrication of such fibres by a multi-dip-coating process has been investigated on platinum wires. The multi-coating process is shown to be more versatile and allows to control the aspect ratio. It is shown that decreasing slurry temperature during the dip process is a suitable way to reduce the number of coating steps in order to achieve high aspect ratio. After sintering, coatings exhibit the same behaviour as bulk ceramics in terms of microstructure, crystallography and ferroelectric loops. © 2014 Elsevier Ltd.

Author Keywords

Actuators; Dip-coating;  Fibres;  Piezoceramics;  PZT

1. Verhaeghe, B., Courtois, C., Petit, F., Cambier, F., Guérin, J.-D., Leriche, A., Hampshire, S.

Lighter tableware ceramic by controlling porosity: Effect of porosity on mechanical properties (2014) Ceramics International, 40 (1 PART A), pp. 763-770. 

Abstract

Reduction in weight of ceramics has been achieved by using a specific porous agent, starch, to achieve porosity ranging from 10% to 35%. Two incorporation routes of the porous agent have been investigated. For different levels of weight reduction, ceramics are characterized by microstructural analysis and mechanical testing. It is shown that the feature of the porous phase mainly depends on the processing route. Two step route leads to the best microstructures and allows ceramics be made up to ten percent lighter without impacting compressive strength (380 MPa) and similar to matrix but with larger variation. © 2013 Published by Elsevier Ltd and Techna Group S.r.l.

Author Keywords

B. Porosity;  C. Mechanical properties;  Lighter tableware ceramic;  Microstructure;  Sustainable porous agent

1. Ashraf, M., Campagne, C., Perwuelz, A., Champagne, P., Leriche, A., Courtois, C.

Development of superhydrophilic and superhydrophobic polyester fabric by growing Zinc Oxide nanorods (2013) Journal of Colloid and Interface Science, 394 (1), pp. 545-553. 

Abstract

ZnO nanorods were grown on microfibers of Polyethylene terephthalate (PET) fabric by seeding method to develop hierarchical roughness structure. XRD and XPS analysis show the presence of crystalline ZnO and chemical Zn species at the fiber surface at each stage of the process. Five series of samples with different seed concentrations have been realized, and their surface morphology and topography were characterized by AFM and SEM. Increasing seed concentrations lead to samples with superhydrophilic properties. Not only the water contact angle at fabric surface tends to zero but also the water capillary diffusion inside fabric is faster. Nanostructuration affects the structure inside the fabric, and further experiments with decane liquid have been made to get a better understanding of this effect. To study the superhydrophobicity, nanorods treated samples were modified with octadecyltrimethoxysilane (ODS) by two method; solution deposition and vapor deposition. The superhydrophobicity was characterized by measuring the water contact angle and water sliding angle with 5 μl water droplet. The samples modified with ODS by vapor deposition showed higher water contact angles and low water sliding angle than the ones modified with solution method. The lotus effect has been well correlated with the surface morphology of the nanorods structured fibers. The application of the Cassie-Baxter equation is discussed. © 2012 Elsevier Inc.

Author Keywords

Capillary diffusion coefficient;  Nanorods; Superhydrophilicity; Superhydrophobicity;  Textile;  Water sliding angle

47) Rguiti, M., Hajjaji, A., D'Astorg, S., Courtois, C., Leriche, A.

Elaboration and characterization of a low frequency and wideband piezoceramic generator for energy harvesting (2013) Optical Materials, 36 (1), pp. 8-12. 

Abstract

The aim of this work was to efficiently convert the mechanical vibrations into electrical energy by using direct piezoelectric effect. Most mechanical vibrations occur at low frequencies varying from 50 to 120 Hz. As piezoelectric converters provide maximum energy conversion when their natural frequencies are close to the frequency of the mechanical source, it would be interesting to design piezoelectric converters operating at low resonance frequencies. For those reasons, a piezoelectric generator has been developed with multi-cantilever piezoceramics operating at low frequencies. The device was shaped using the tape casting technique followed by a laser cutting process. It was made of six piezoelectric cantilevers with different lengths and various masses at their free-ends. Its piezoelectric response was characterized and analysed. It was shown that it can operate at low and many resonant frequencies. Moreover the frequency bandwidth was widened up to 200% compared to the one obtained from a single cantilever beam. It allowed efficiently exploiting mechanical vibrations of sources exhibiting wide frequency spectrum. © 2013 Elsevier B.V. All rights reserved.

Author Keywords

Energy harvesting; Laser cutting;  Multi-cantilever sensor;  Piezoelectric ceramic;  Tape casting

1. Lidjici, H., Hobar, F., Rguiti, M., Courtois, C., Leriche, A.

Solid state sintering prepared 0.935(Bi 0.5Na 0.5) TiO 3-0.065BaTiO 3 lead free ceramics: Effect of poling conditions (2012) Ceramics - Silikaty, 56 (1), pp. 36-39. 

Abstract

In this work , the influence of poling conditions (poling field, poling temperature and poling time) on the piezoelectric properties of 0.935(Bi 0.5Na 0.5) TiO 3-0.065BaTiO 3 (BNT6.5BT) lead-free ceramics was examined. Piezoelectric properties like piezoelectric constant (d 33) and electromechanical factors (K p ,K t ) depend on poling field and poling temperature, whereas different poling times, in the 5-30 min range, were not observed to have significant effect on the piezoelectric properties.

Author Keywords

Lead free ceramics; Piezoelectric properties;  Poling conditions

1. Trelcat, J.-F., Courtois, C., Rguiti, M., Leriche, A., Duvigneaud, P.-H., Segato, T.

Morphotropic phase boundary in the BNT-BT-BKT system (2012) Ceramics International, 38 (4), pp. 2823-2827. 

Abstract

Lead-free x Bi 0.5Na 0.5TiO 3-y BaTiO 3-z Bi 0.5K 0.5TiO 3 piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 - x) BNT-x BT solid solution ceramics, the 0.94 BNT-0.06 BT morphotropic composition shows the higher values with d 33 = 170 pC/N, k p = 0.35 and k t = 0.53. In the case of (1 - x) BNT-x BKT compositions, the d 33, k p and k t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT-0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT-0.035 BT-0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d 33 = 133 pC/N, k p = 0.26 and k t = 0.57). © 2011 Elsevier Ltd and Techna Group S.r.l.

Author Keywords

Barium titanate; Bismuth potassium titanate; Bismuth sodium titanate;  C. Electrical properties;  C. Piezoelectric properties;  Lead-free;  Morphotropic phase boundary;  Piezoelectric ceramics;  Solid state reaction

50) Hajjaji, A., Rguiti, M., Boughaleb, Y., Sassi, Z., D'Astorg, S., Ly, R., Courtois, C., Moreau, G., Leriche, A.

Micro-macro correlation in ferroelectric materials: Depolarization mechanism owing mechanical stress (2011) Sensor Letters, 9 (6), pp. 2190-2193. 

Abstract

Piezoelectric ceramics are commonly used in numerous piezoelectric actuators and sensors. Most ferroelectric materials behave as piezoelectric for low driving levels. The increase of electric field, temperature or stress levels leads to a depoling and results in some degradation of dielectric and piezoelectric performances. It is usually considered that this latter phenomenon is due to the irreversible domain wall motion as well as nucleation and growth of new domains. The domain configuration of ferroelectric materials significantly influences their behaviour under compressive stress, electric field and temperature driving. A fine description of domain organization can help to understand the piezoelectric and dielectric responses. The purpose of this work is to analyse these phenomena throughout a multi-scale approach. Microscopic, X-ray measurements have been performed on several ceramics with different crystallographic symmetries in order to evaluate the percentage of switched domains (PSD). The macroscopic polarization state was simulated from PSD and compared to experimental results. An estimation of depolarization mechanisms under stress is proposed. From these results, it can be concluded that domain switching induced by compressive stress was mainly controlled by the mechanical applied stress. Dipole-dipole interactions appear to be no predominant. In addition, influences of temperature and electric field are analysed. Copyright © 2011 American Scientific Publishers All rights reserved.

Author Keywords

Ceramic; Depolarization;  Domain switching;  Piezoelectric

1. Ferguen, N., Cogné, C., Guessasma, M., Bellenger, E., Pélegris, C., Outirite, M., Courtois, C., Rigot, O., Hoquet, S.

Manufacture of alumina/aluminum functionally graded material: Numerical investigation of the architecture and evaluation of the thermal conductivity

(2011) Materials Science and Technology Conference and Exhibition 2011, MS and T'11, 2, pp. 1623-1633. 

Abstract

A numerical model is proposed for modeling functionally graded materials (FGMs) in which the architecture of the FGMs is obtained from a granular material composed of overlapping spherical particles as skeletal structure. The numerical approach is based on both discrete element method (DEM) and finite element method (FEM). The model is able to simulate the different steps of the elaboration process of the FGMs. The aim of this work is to obtain a FGM alumina/aluminum with an optimized architecture in order to improve the thermal properties. In this study, heat transfer of the material composite is achieved by the FEM in order to assess the effective thermal conductivity (ETC). Effects of the particles size and the contact radius of the interconnected particles are investigated. Copyright © 2011 MS&T'11®.

Author Keywords

Ceramic;  FGMs;  Modeling; Thermal conductivity

1. Trelcat, J.-F., d'Astorg, S., Courtois, C., Champagne, P., Rguiti, M., Leriche, A.

Influence of hydrothermal synthesis conditions on BNT-based piezoceramics (2011) Journal of the European Ceramic Society, 31 (11), pp. 1997-2004. 

Abstract

The Bi0.5Na0.5TiO3 perovskite (BNT) is a very promising lead-free candidate for piezoelectric applications. Nevertheless a low reproducibility is commonly reported for the solid state synthesized BNT. In this work, the hydrothermal synthesis was investigated to improve the BNT ceramics characteristics reproducibility. The synthesis conditions were studied in order to control more particularly the BNT grain size, crystallinity and stoichiometry. Thanks to the slow hydrolysis of titanium isopropoxide with bismuth nitrate pentahydrate, well crystallized BNT-based powder was synthesized at 265°C. Nevertheless this powder exhibited secondary amorphous phases. Such secondary phases synthesis was limited and prevented by both lowering the temperature synthesis down to 160°C and optimizing the washing conditions of the powder. The BNT was finally made free of any amorphous phase by using a hydrochloric solution. The BNT sinterability was improved and BNT-based piezoceramics exhibiting a d33 as high as 60pC/N were successfully produced. © 2011 Elsevier Ltd.

Author Keywords

BNT;  Electrical properties;  Hydrothermal synthesis;  Lead-free; Piezoelectric properties

53) Chaouchi, A., Kennour, S., D'Astorg, S., Rguiti, M., Courtois, C., Marinel, S., Aliouat, M.

Characterization of sol-gel synthesised lead-free (1 - X)Na 0.5Bi0.5TiO3-xBaTiO3-based ceramics (2011) Journal of Alloys and Compounds, 509 (37), pp. 9138-9143. 

Abstract

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 - x)Na0.5Bi0.5TiO3-xBaTiO 3 ceramics with x = 0, 0.03, 0.05, 0.07 and 0.1 are investigated. A structural variation according to the system composition was investigated by X-ray diffraction (XRD) analyses. The results revealed that the synthesis temperature for pure perovskite phase powder prepared by the present sol-gel process is much lower (800 °C), and a rhombohedraltetragonal morphotropic phase boundary (MPB) is found for x = 0.07 composition which showing the highest remanent polarization value and the smallest coercive field. The optimum dielectric and piezoelectric properties were found with the 0.93Na 0.5Bi0.5TiO3-0.07BaTiO3 composition. The piezoelectric constant d33 is 120 pC/N and good polarization behaviour was observed with remanent polarization (Pr) of 12.18 pC/cm2, coercive field (Ec) of 2.11

kV/mm, and enhanced dielectric properties εr &gt; 1500 at room temperature. The 0.93Na0.5Bi0.5TiO3-0.07BaTiO3-based ceramic is a promising lead-free piezoelectric candidate for applications in different devices. © 2011 Elsevier B.V. All rights reserved.

Author Keywords

Dielectrics; Ferroelectric;  Lead-free ceramics;  Na0.5Bi0.5TiO3;  Sol-gel

54) Ly, R., Rguiti, M., D'Astorg, S., Hajjaji, A., Courtois, C., Leriche, A.

Modeling and characterization of piezoelectric cantilever bending sensor for energy harvesting (2011) Sensors and Actuators, A: Physical, 168 (1), pp. 95-100. 

Abstract

The main aim of this work is to enhance the conversion of mechanical energy into electrical energy by using direct piezoelectric effect. Under the

assumption of the Euler-Bernoulli Beam Theory, a piezoelectric cantilever bending of 31-effect was developed. The equations of motion for the global system were established by using Hamilton's principle and solved by using the modal decomposition method. It provided the transfer functions model between the inputs (force) and the outputs (voltage) allowing the description of its dynamic behaviour for energy harvesting. The model was implemented by using Matlab software and will be able to integrate with the circuit model of energy storage. The results obtained show a good agreement with the experiments and other previous works. The model and the experiment indicate that the second mode of resonant frequency provides the voltage and the bandwidth much larger than the first mode. While the mass at the free end increases, the voltage obtained by the first mode increases. In contrast, the voltage obtained by the second mode decreases. © 2011 Elsevier B.V. All rights reserved.

Author Keywords

Analytical model; Bending sensor;  Energy harvesting;  Euler-Bernoulli Beam Theory;  Piezoelectric cantilever

1. Lidjici, H., Rguiti, M., Hobar, F., Trelcat, J.-F., Courtois, C., Leriche, A.

The effects of sintering temperature and poling condition on the piezoelectric properties of 0.935(Bi 0.5Na 0.5)TiO 3 - 0.065BaTiO 3 ceramics (2011) Materials Science- Poland, 29 (1), pp. 9-14. 

Abstract

The 0.935(Bi 0.5Na 0.5) TiO 3 -0.065BaTiO 3 (abbreviated as BNT6.5BT) lead-free ceramics were prepared by conventional solid state sintering technique. The effects of sintering temperature (1150-1200 °C) and poling condition on its piezoelectric properties were examined. Piezoelectric properties like the piezoelectric constant (d 33) and electromechanical factors (k p, k t) depend on the poling field and poling temperature, whereas different poling times, in the 5-30 min range, were not observed to have any significant effect on the piezoelectric properties. With respect to piezoelectric properties, the chosen sintering temperature range is suitable for BNT6.5BT ceramics. © Wroclaw University of Technology.

Author Keywords

Dielectric and piezoelectric properties;  Lead free ceramics;  Poling condition;  Sintering temperature

1. Hajjaji, A., Rguiti, M., Courtois, C., Boughaleb, Y., Dastorg, S., Kobor, D., Leriche, A.

A polycrystal hysteresis model based on the Landau theory for ferroelectric ceramics (2011) Journal of Optoelectronics and Advanced Materials, 13 (3), pp. 313-318. 

Abstract

Most key elements of ferroelectric properties are defined through the hysteresis loops. For polycrystalline ceramics, each grain exhibits a specific loop and contributes to the ferroelectric ceramic's one. The resulting hysteresis loop is influenced both by the frequency and temperature. In this paper, we propose a polycrystal hysteresis model describing the hysteresis in ferroelectric materials as a function of the temperature and frequency. This model, based on the Landau phenomenological thermodynamic potential theory, allows determining the behaviors of ceramics. This theory differs from the classical phenomenological ones : it is a macroscopic -based thermodynamic approach and it can provide the evolution of polarization state, and other coefficients as a function of electric field, temperature and frequency simultaneously. The proposed model is developed, discussed, and compared with experimental piezoelectric characterizations on a PZT based piezoelectric transducer ceramic. Hysteresis loop comparisons between modeling and experimental data are given and are shown to be in good agreement with the polarization versus electric field and temperature. It is interesting to note that the model developed in this paper could also predict the dielectric constant (ε33) as a function of the electric field using a simple P(E) measurement.

Author Keywords

Hysteresis model; Landau phenomenological theory; Polycrystal

57) Devemy, S., Courtois, C., Champagne, P., Moreau, G., Leriche, A.

Flux growth mechanisms of PZT cubic grains (2011) Powder Technology, 208 (2), pp. 351-354. 

Abstract

Growth in a PbO flux is an appropriate method to synthesize large cubic grains of Pb(ZrxTi1-x)O3. An application could be PZT-based piezoceramics texturation. In order to optimize this synthesis, the flux synthesis has to be understood. In this study, water quenchings of PbO flux synthesis were realized at every stage of the thermal cycle including 6 steps. The oxide powders (PbO, ZrO2 and TiO2) were mixed and quickly heated up to 1200°C for 2h. The flux was then slowly cooled down to 900°C for 10h. Further cooling down to 750°C was followed by a natural cooling to room temperature.SEM observations, X-EDS analysis and X-ray diffraction were performed on the PZT powders after each quench showing several specific growth sequences. © 2010.

Author Keywords

Flux;  Growth;  Mechanism; PZT;  Texture

58) Lidjici, H., Rguiti, M., Hobar, F., Courtois, C., Leriche, A.

Solid state sintering prepared 0.935(Bi0.5Na0.5) TiO3-0.065BaTiO3 lead-free ceramics: Effect of sintering temperature (2010) Ceramics - Silikaty, 54 (3), pp. 253-257. 

Abstract

The effects of sintering temperature on structure, microstructure, dielectric and piezoelectric properties of 0.935(Bi0.5 Na 0.5)TiO3-0.065BaTiO3

(BNT6.5BT) lead free ceramics prepared by solid sintering technique at 1150-1200°C were investigated. The X-ray diffraction patterns showed that all of the BNT6.5BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. A fine and homogeneous grains were observed for samples sintered at 1150 and 1160°C and the increase of the sintering temperature up to 1180-1200°C induces significant grain growth with the appearance of coarse grains. The dielectric constant- temperature curves of the compositions exhibited strong dispersion with the increasing temperature, and the dielectric loss increased dramatically while the temperature over 230°C. The lowest value of depolarization temperature (Td) was found at samples sintered at 1160°C. The values of remnant polarization Pr obtained at room temperature are 31 and 29 μC/cm2 for specimens sintered at 1160°C and 1200°C respectively. At room temperature, BNT6.5BT ceramics sintered at 1180°C exhibited good performances: dielectric constant was 833 at 1 KHz, thick coupling factor kt was 0.52 and the k t/kp ratio was 2.08. Therefore, the ceramics can be suitable for ultrasonic transducers in commercial applications.

Author Keywords

Dielectric and piezoelectric properties;  Lead-free ceramics;  Sintering temperature

1. Hajjaji, A., Guyomar, D., Touhtouh, S., Pruvost, S., Boughaleb, Y., Rguiti, M., Courtois, C., Leriche, A., Benkhouja, K.

Nonlinearity and scaling behavior in a soft lead zirconate titanate piezoceramic (2010) Journal of Applied Physics, 108 (6), art. no. 064103, . 

Abstract

Lead oxide-based ferroelectrics, represented by lead zirconate titanate [Pb (Zr,Ti) O3] or PZT), are the most widely used materials for piezoelectric actuators, sensors, and transducers due to their excellent piezoelectric properties. Most of these piezoelectric materials are employed under a variety of strains (stress, electrical field, and temperature). It would thus be interesting to predict their behaviors under different excitations without having to perform too much experimental work, i.e., just carry out a single experiment and still be able to provide the other experimental values. The purpose of this paper has thus been to propose several behavioral laws linking the electrical field, temperature and mechanical stress. The first law rendered it possible to express the mechanical stress by an equivalent electric field [ΔEα ΔT×P (E, T0)]. Subsequently, a law linking the electrical field and temperature { ΔE [2Β×P (E, θ0)] ×Δθ } was proposed. From these two laws, a third law was identified reflecting the mechanical stress as an equivalent temperature; each expressed by a temperature equivalent stress (Tδ×Δ θ). After experimental validation of these laws, the mapping could be extended in order to predict the polarization behavior in the tensile stress zone as well as that as a function of the negative temperature. © 2010 American Institute of Physics.

1. Moreschi, V., Lalot, S., Courtois, C., Leriche, A.

Modelling the tap density of inorganic powders using neural networks (2009) Journal of the European Ceramic Society, 29 (15), pp. 3105-3111. 

Abstract

In the present study, the tap relative density of five inorganic powders is modelled using neural networks. These powders are similar in shape but have different true density. A large number of mixings are prepared from three classes (coarse, medium, and fine particles) and modelled. The inputs of the neural networks are the 23 weight percentage intervals of the grain size distribution (38-2000 μm). The estimated values are compared to those obtained by factorial plans. It is shown that very accurate results are obtained with a unique relatively small neural network. Finally, the neural network is used to determine the mixing leading to the highest tap relative density. © 2009 Elsevier Ltd. All rights reserved.

Author Keywords

Inorganic powder; Modelling;  Neural network;  Tap relative density

1. Devemy, S., Courtois, C., Champagne, P., Lippert, M., Moreau, G., Petit, F., Leriche, A.

Textured PZT ceramics

(2009) Powder Technology, 190 (1-2), pp. 141-145. 

Abstract

The purpose of this study is to make a textured PZT ceramic starting from tape cast sheet in order to improve their piezoelectric properties. PZT powders with cubic morphology are synthesized by flux growth. XRD and X-EDS analysis show that the obtained grains have a size which can reach 70 μm and present an tetragonal structure, with the Pb(Zr0,44Ti0,56)O3 composition. The slurry made from these particles is tape cast on a « Doctor Blade » bench. The last stage consists in densifying the samples. Reorganization of large-size grains during sintering being difficult, the densification turns out to be delicate to operate by natural sintering. More sophisticated methods as hot pressing are used to improve the densification. Both techniques, natural sintering and hot pressing, are compared. The realized samples are characterized by SEM, X-ray diffraction, specific surface area and density measurements, and piezoelectric coefficient d33 measurements. © 2008 Elsevier B.V. All rights reserved.

Author Keywords

Densification; Flux;  PZT;  Sintering; Textured

1. Bataille, A., Addad, A., Courtois, C., Duhoo, T., Crampon, J.

Solute and defect segregation at the space charge layers of Fe-doped fine-grained Al2O3: Effect on the creep rate (2008) Journal of the European Ceramic Society, 28 (6), pp. 1129-1134. 

Abstract

Compressive creep in air of vacuum hot-pressed undoped alumina and 0.5 at.% iron doped alumina materials was investigated. The dark green colour of doped alumina accounted for the presence of iron as Fe2+ species at first. Also, iron rich precipitates were observed and identified as FeAl2O4 spinel. During the tests, Fe2+ species underwent oxidation during creep. The space charge concept is developed to account for the data and the interaction between the space charge and the extrinsic defect species. The observed iron segregation is proposed in the subgrain boundary region. Iron spinel precipitates were observed interacting with grain boundaries. Oxidation of Fe2+ resulted in Fe3+, which segregated into the grain boundaries. This segregation produced creep resistance of alumina. © 2007 Elsevier Ltd. All rights reserved.

Author Keywords

Al2O3;  Creep;  Defects; Grain boundary;  Space charge

63) Courtois, C., Devemy, S., Champagne, P., Lippert, M., Rguiti, M., Leriche, A., Chateigner, D., Guilmeau, E.

Comparison of two molten flux process for the elaboration of textured PZT thin plates (2007) Journal of the European Ceramic Society, 27 (13-15), pp. 3779-3783. 

Abstract

In this paper, we describe a new protocol for the elaboration of textured PZT thin plates. This protocol is based on three steps: (i) powder synthesis, (ii) tape casting/lamination in green state and (iii) sintering/densification. Powder synthesis is operated through a specific molten flux method, which in optimised conditions allows the crystallisation of coarse and cubic shape grains of PZT. The powder is extracted from the flux by acidic attack, washing and filtration. It is used as raw material to elaborate a slip with organic media in order to achieve thick tapes that exhibit preferred orientations of the PZT phase. The crystallographic textures are measured on a four-circle X-ray diffractometer and determined using the so-called "combined approach" that uses Rietveld and orientation distribution function refinements. © 2007 Elsevier Ltd. All rights reserved.

Author Keywords

Flux synthesis; Microstructure prefiring;  PZT

64) Courtois, C., Crampon, J., Champagne, P., Cochrane, C., Texier, N., Leriche, A.

STEM-X-EDS analysis of morphotropic PZT ceramics. Analysis of Zr/Ti + Zr values fluctuation depending on microstructure and synthesis route of powders

(2006) Ceramics International, 32 (7), pp. 767-773. 

Abstract

A TEM-EDS analysis technique is applied to estimate dopant incorporation and Zr/Zr + Ti fluctuation in morphotropic PZT ceramics starting from powders synthesized by two routes. A solid-state synthesis route leads to less reactive powders requiring severe conditions to reach full densification. The hydrothermal route leads to more reactive powders that can be fully densified at lower temperature. In addition, the influence of Ni addition was analyzed. Zr/Zr + Ti fluctuations were estimated by the standard deviation of concentrations carried out by chemical analyses. It was shown that there is no significant partitioning of Zr and Ti inside a grain or in the ceramic. Each PZT material appears to be homogenous with a constant value of standard deviation of Zr/Zr + Ti ratios. The obtained values depend mainly on the presence or not of Ni addition whatever the nature of the chosen synthesis route. Standard deviation values of Zr/Zr + Ti ratios appear to be in accordance with literature values estimated by high temperature X-ray diffraction broadening. Results are also discussed relatively to some piezoelectric properties and more particularly to the quality mechanical factor. © 2005.

Author Keywords

A. Powders: chemical preparation;  B. Electron microscopy;  B. X-ray methods;  D. PZT

1. Rodriguez, R., Carrerot, H., Courtois, C., Leriche, A.

Effect of grinding parameters on the surface integrity and flexural strength of silicon nitride (2005) Industrial Diamond Review, 65 (2), pp. 49-52+56. 

Abstract

Silicon nitride ceramics exhibit a series of interesting properties such as low density, high thermal shock resistance, high rupture resistance and good wear behaviour. These properties can be exploited from room to high temperature (less than 1000 °C) to enable the material to be used for cutting tools, engine parts or bearings applications. To date, the different process steps for the fabrication of silicon nitride parts are well known and obtaining the precise final dimension and shape often requires a finish grinding operation. This paper, by R. Rodriguez, H. Carrerot, C. Courtois and A. Leriche, sets out to study the influence of grinding parameters (depth of cut and feed rate of the workpiece) on the silicon nitride material in terms of surface damage and flexural strength. The experimental results show that the mechanical properties remain unchanged and the surface damage decreases for 'hard' or very severe grinding conditions.

1. Guillon, O., Thiebaud, F., Perreux, D., Courtois, C., Champagne, P., Leriche, A., Crampon, J.

New considerations about the fracture mode of PZT ceramics

(2005) Journal of the European Ceramic Society, 25 (12 SPEC. ISS.), pp. 2421-2424. 

Abstract

Sintered bulk ceramics, such as PZT are brittle materials. This macroscopically implies a statistical distribution of the ultimate strengths, because defects, such as pores or cracks are responsible for the initiation of the specimen failure. Another aspect of this fracture phenomenon is the crack propagation inside the material, along grain boundaries or through the grains themselves. An experimental study was carried out on hard and soft PZT by means of a scanning electron microscopy (SEM) quantitative analysis of tensile fractured areas. This reveals that the fracture mode is mixed, although it seems to be rather intragranular for hard ceramics and more intergranular for soft ones. Further investigations deal with the characterization of the residual porosity, which has to be distinguished from the population of critical defects. This porosity is located at grain boundaries and likely acts also as a stress concentrator and has an effect on the fracture mode and mechanical properties. For doped hard and soft PZT, a careful analysis of the microstructure is thus achieved through transmission electron microscopy (TEM) micrographs. Furthermore, domain structure is analysed for hard and soft PZT. © 2005 Elsevier Ltd. All right reserved.

Author Keywords

Electron microscopy; Fracture;  Grain boundaries;  Porosity; PZT

1. Mandoki, N.T., Courtois, C., Champagne, P., Leriche, A.

Hydrothermal synthesis of doped PZT powders: Sintering and ceramic properties (2004) Materials Letters, 58 (20), pp. 2489-2493. 

Abstract

We present here the sintering behaviour, the ceramic characteristics and the electrical properties of PZT prepared from new hydrothermal powders. These results are compared with classical calcined ceramic properties. PZT powders are doped corresponding to the formula Pb((Zr0.49Ti0.51) 0.94Mn0.0252Sb0.0192W0.0156)O 3 with or without 0.8758 mol% Ni. © 2004 Elsevier B.V. All rights reserved.

Author Keywords

Ceramic;  Electrical properties;  Hydrothermal powders;  Microstructure;  Perovskite; Piezoelectric materials; PZT;  Sintering

1. Texier, N., Courtois, C., Traianidis, M., Leriche, A.

Powder process influence on the characteristics of Mn, W, Sb, Ni-doped PZT (2001) Journal of the European Ceramic Society, 21 (10-11), pp. 1499-1502. 

Abstract

The use of lead zirconate titanate ceramics for applications like actuators implies the development of materials with high mechanical quality factor Qm and high electromechanical coupling coefficient kp. The composition Pb(Zr0.49Ti0.51)0.94Mn0.0252 Sb0.0192 W0.0156)O3+0.2 wt.% NiO has been studied with this aim in view. Homogeneous, fine and desagglomerated powders are required. A new doped PZT powder elaboration process by hydrothermal route has been developed. The same composition is also prepared by a conventional calcination route. The chemical and physical characteristics of these two kinds of powders are studied and the sintering behaviour has been investigated. Ceramics from the hydrothermal route densify at 850°C while the ceramics from the calcined powders require a sintering temperature of 1150°C. The microstructures were studied and the piezoelectric and ferroelectric properties were determined. © 2001 Elsevier Science Ltd. All rights reserved.

Author Keywords

Electrical properties; Microstructure-final; Piezoelectric properties; Powders-chemical preparation;  PZT

1. Kermel, C., Courtois, C., Möltgen, P., Leriche, A.

Sol-gel elaboration and characterisation of Al2O3/SiC nano- and microcomposites for wear applications (2001) Key Engineering Materials, 206-213 (II), pp. 1005-1008. 

Abstract

The polycondensation reaction of a boehmite sol, a sol-gel process, was used to fabricate nanocomposite xerogels. The process was developed and optimised so that good dispersion of SiC in the xerogel was obtained. Different sizes (from 30 μm down to 480 nm) of SiC powders were used as reinforcing phase in the alumina matrix. Improvement of the performance of sol-gel abrasive grits can be achieved by including SiC nanosized particles. It was although observed that decreasing the content of the freest SiC powders (nanosized) led to an increase in the wear performance whereas no correlation between performance and SiC amount was observed for the coarser inclusions.

Author Keywords

Abrasive grits; Alumina;  Boehmite;  Composites; Nanocomposites;  Silicon carbide;  Sol-gel;  Wear

1. Texier, N., Courtois, C., Traianidis, M., Leriche, A.

Influence of powder synthesis route on the reactivity and the electrical properties of PZT ceramics (2001) Key Engineering Materials, 206-213 (II), pp. 1485-1488. 

Abstract

High temperatures (above 1200°C) are needed to densify PZT ceramics. At these temperatures the volatility of PbO during sintering is quite serious, which leads to deteriorate the properties of ceramics and to pollute the environment. In that way, it is opportune to develop more reactive powders to allow the fabrication of dense and homogeneous PZT ceramics at low temperature. We present here the sintering behaviour and the electrical properties of PZT ceramics prepared from new hydrothermal powders. These results are compared with classical calcined ceramic properties.

Author Keywords

Electrical properties; Hydrothermal powders;  PZT;  Sintering

1. Traianidis, M., Courtois, C., Leriche, A.

Mechanism of PZT crystallisation under hydrothermal conditionsDevelopment of a new synthesis route (2000) Journal of the European Ceramic Society, 20 (16), pp. 2713-2720. 

Abstract

On the basis of a 1-stage hydrothermal process, we first investigated the reaction mechanism responsible for the PZT precipitation. In a first sequence, lead diffuses into the amorphous coprecipitate. By increasing the reaction temperature, these particles dissolve, leading to nucleation and growth of PZT well faceted particles. In a second step, we demonstrated that starting from very fine oxide precursors, a homogeneous PZT solid solution could be formed. Under the same conditions but without any lead precursor, a mixture of KTO (a potassium titanium oxide phase) and tetragonal zirconia is formed. A 2-stage process was developed on these assumptions. The first stage consists in producing the KTO-ZrO2(T) mixture. In the second stage, this mixture is hydrothermally treated in presence of lead precursor. Pure and homogeneous PZT and PLZT powders were obtained throughout this new synthesis route. © 2000 Elsevier Science Ltd.

Author Keywords

Chemical composition; Crystallisation mechanism;  Dopant integration;  Hydrothermal;  Lanthanum; PLZT;  Powders-chemical preparation;  Precursorsorganic;  Precursors-oxides;  PZT

1. Courtois, C., Traianidis, M., Texier, N., Lefort, V., Tardot, A.

Analyse de PZT morphotropique par diffraction X haute temperature: influence du procede d'elaboration sur la dispersion chimique (2000) Journal De Physique. IV : JP, 10 (10), pp. 81-88. 

1. Pinceloup, P., Courtois, C., Leriche, A., Thierry, B.

Hydrothermal synthesis of nanometer-sized barium titanate powders: Control of barium/titanium ratio, sintering, and dielectric properties (1999) Journal of the American Ceramic Society, 82 (11), pp. 3049-3056. 

Abstract

Nanometer-sized BaTiO3 powders have been synthesized hydrothermally from Ba(OH)2 and titanium alkoxide at 150 °C for 2 h, and the Ba/Ti ratio has been measured with an accuracy of ±0.003. Stoichiometric powders can be obtained by adjusting the Ba/Ti ratio of the reactants to a value of 1.018. At a lower Ba/Ti ratio, the solubility of Ba(OH)2 prevents full incorporation of barium, and barium-deficient powders result. A higher Ba/Ti ratio leads to the incorporation of excess barium in the powder. Ks(BaTiO3,-25 °C) = 7×10-8 has been calculated for the equilibrium reaction. From this result, two reproducible processes for the synthesis of stoichiometric BaTiO3 are proposed. The processes rely only on very accurate control of the chemical composition (Ba/Ti ratio) of the precursor suspension. The sintering behavior of powders having Ba/Ti ratio values between 0.965 and 1.011 is described from results of dilatometric measurements and isothermal sintering. Room-temperature dielectric constants as high as 5600 and losses as low as 0.009 have been obtained for a stoichiometry slightly less than 1.000. It is expected that optimum sintering behavior and electrical properties are obtained in the stoichiometry range 0.995-1.000.

1. Pinceloup, P., Courtois, C., Vicens, J., Leriche, A., Thierry, B.

Evidence of a dissolution-precipitation mechanism in hydrothermal synthesis of barium titanate powders (1999) Journal of the European Ceramic Society, 19 (6-7), pp. 973-977. 

Abstract

In our study of the system barium hydroxide-titanium tetraisopropoxide-water-isopropanol between 85 and 150°C, we have observed the following evidence of a mechanism by dissolution-precipitation: (1) when varying the water/isopropanol ratio in synthesis at 150°C, the grain size of barium titanate decreases when the amount of alcohol increases, i.e. when the solubility of the precursors decreases; (2) TEM observations of incompletely reacted powders showed that the grains are either amorphous or entirely crystalline BaTiO3, which means that homogeneous nucleation and growth is occurring instead of heterogeneous nucleation; (3) high resolution TEM observations of fully reacted powders revealed the presence of necks between particles. These three experimental observations in the same reaction system provide strong evidence of dissolution-precipitation as the primary reaction mechanism.

Author Keywords

BaTiO3 and titanates.; Electron microscopy; Powders-chemical preparation; Precursors-organic

75) Traianidis, M., Courtois, C., Leriche, A., Thierry, B.

Hydrothermal synthesis of lead zirconium titanate (PZT) powders and their characteristics (1999) Journal of the European Ceramic Society, 19 (6-7), pp. 1023-1026. 

Abstract

The combined influences of KOH initial concentration and initial lead precursor excess on the characteristics (morphology, powder density, specific surface area, crystalline structure and powder chemical composition) and sintering behaviour of hydrothermally synthesised powders, have been investigated. Optimised conditions (low KOH concentration and presence of lead excess in the feedstock) have been determined that lead to fine deagglomerated and reactive PZT powders densifying at about 850°C. A Pb-rich surface layer has been identified over the grains, that is responsible for this low sintering temperature. Despite the large excess of lead, the core of powders remains lead deficient. But by lowering [KOH]o, it is possible to keep the lead deficiency within a few percent.

Author Keywords

Chemical composition; Powders-chemical preparation; Precursors-organic;  PZT.;  Sintering

Thème de recherche :

- amélioration des propriétés d'usage de certains matériaux céramiques - massives ou en couche - par une optimisation intégrée de l'ensemble de leur protocole d'élaboration