Effect of thermal annealing on dielectric and ferroelectric properties of aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O3−0.35PbTiO30.65\text{Pb}(\text{Mg}_{1/3}\text{Nb}_{2/3})\text{O}_{3}-0.35\text{PbTiO}_{3} thick films

In this work, the effects of thermal annealing at 500 {\deg}C on aerosol-deposited $0.65\text{Pb}(\text{Mg}_{1/3}\text{Nb}_{2/3})\text{O}_{3}-0.35\text{PbTiO}_{3}$ thick films on stainless-steel substrates are investigated using two complementary methods at high and low applied external electric fields. The first one is Positive Up Negative Down method, which allows us to obtain information about the switching and non-switching contributions to the polarization. It shows that the as-deposited film is ferroelectric before annealing, since it has a switching contribution to the polarization. After annealing, both the switching and non-switching contributions to polarization increased by a factor of 1.6 and 2.33, respectively, indicating stronger ferroelectric behavior. The second method is based on impedance spectroscopy coupled with Rayleigh analysis. The results show that post-deposition thermal annealing increases the reversible domain wall contribution to the dielectric permittivity by a factor 11 while keeping the threshold field similar. This indicates, after annealing, domain wall density is larger while domain wall mobility remains similar. These two complementary characterization methods show that annealing increases the ferroelectric behavior of the thick film by increasing the domain wall density and its influence is visible both on polarization versus electric field loop and dielectric permittivity

High temperature piezoelectric properties of flux-grown α-GeO 2 single crystal

International audienceThe temperature-dependence of the piezoelectric properties of trigonal -GeO2 single-crystals obtained by the high-temperature flux method was measured by the resonance technique of the electrical impedance in the 20°C-600°C range. To approach the values of the two independent piezoelectric coefficients d11 and d14, we first measured as a function of temperature the elastic coefficients S11, S14 and S66 and the dielectric permittivity 11 which are involved in the coupling coefficient k of both the thickness shear mode and the transverse mode. A Y-cut plate with a simple +45°-rotation ((YXtwl) +45°/0°/0°) was used to measure the coupling coefficient of the thickness shear mode, and two X-turned plates ((XYtwl) +45°/0°/0° and (XYtwl)-45°/0°/0°) were prepared to characterize the coupling coefficient of two transverse modes. From the whole experimental measurements, the piezoelectric coefficients of -GeO2 were calculated up to 600 °C. They show that this crystal is one of the most efficient in regard of the -quartz-like family at room temperature, and that its thermal comportment retains large piezoelectric properties up to 600°C

Synthesis and functional properties of lead free piezoelectric (K,Na)NbO3 ceramics and single crystals

Ce travail a pour objectif d’élaborer de manière contrôlée différentes microstructures de (K0,5Na0,5)NbO3 non dopées par différentes mises en forme, bien caractérisées structuralement et microstructuralement, afin d’étudier et d’éclaircir l’influence de la densification et de la taille des grains sur les propriétés piézoélectriques. Il s’agit pour cela de produire des microstructures, avec une composition maitrisée, ayant d’abord des grains de taille micrométrique, ensuite millimétrique et enfin si possible des grains centimétriques de KNN et d’atteindre des densifications allant de 80 % à plus de 95 %. Au-delà de l’ingénierie des microstructures de KNN, l’obtention de monocristaux du composé (K0,5Na0,5)NbO3 de plusieurs mm3, de bonne qualité cristalline et bien caractérisés structuralement et microstructuralement permettrait de caractériser l’ensemble des tenseurs élastiques, diélectriques et piézoélectriques ainsi que de valider des méthodes de caractérisation originales développées au sein du laboratoire GREMAN.The purpose of this work is to elaborate different controlled microstructures of undoped (K0,5Na0,5)NbO3 by different methods, with full structural and microstructural characterization in order to study and to elucidate the influence of the densification and grain size effect on the piezoelectric properties. For this, it is necessary to produce KNN microstructures with controlled composition, starting with micrometer grain size, then millimeter and if possible centimeter grain size and to attain densification ranging from 80 % up to 95 % of the theoretical one. Beyond the KNN microstructure engineering, the growth of large (K0,5Na0,5)NbO3 single crystals about several mm3 with good crystallinity and full structural and microstructural characterization would enable the elastic, dielectric and piezoelectric tensors to be fully characterized as well as to validate the original characterization methods developed within the GREMAN laboratory

Electrical, morphological and structural properties of Ti ohmic contacts formed on n-type 4H–SiC by laser thermal annealing

International audienc

Effect of thermal annealing on dielectric and ferroelectric properties of aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O3-0.35 PbTiO3 thick films

International audienceIn this work, the effects of thermal annealing at 500°C on aerosol-deposited 0.65Pb(Mg1/3Nb2/3)O 3-0.35PbTiO 3 thick films on stainless-steel substrates are investigated using two complementary methods at high and low applied external electric fields. The first one is Positive Up Negative Down method, which allows us to obtain information about the switching and non-switching contributions to the polarization. It shows that the as-deposited film is ferroelectric before annealing, since it has a switching contribution to the polarization. After annealing, both the switching and non-switching contributions to polarization increased by a factor of 1.6 and 2.33, respectively, indicating stronger ferroelectric behavior. The second method is based on impedance spectroscopy coupled with Rayleigh analysis. The results show that post-deposition thermal annealing increases the reversible domain wall contribution to the dielectric permittivity by a factor 11 while keeping the threshold field similar. This indicates, after annealing, domain wall density is larger while domain wall mobility remains similar. These two complementary characterization methods show that annealing increases the ferroelectric behavior of the thick film by increasing the domain wall density and its influence is visible both on polarization versus electric field loop and dielectric permittivity

Metastable and field-induced ferroelectric response in antiferroelectric lead zirconate thin film studied by the hyperbolic law and third harmonic response

In this paper, the field-induced residual ferroelectricity in antiferroelectric lead zirconate thin films has been studied by impedance measurements together with a hyperbolic law analysis, which permits us to extract the different contributions to the material’s complex permittivity. By measuring the Rayleigh coefficient αr, it appears that the residual ferroelectricity is considerably enhanced when the sample has been previously exposed to an electric field close to the antiferroelectric to ferroelectric transition field. This indicates that a part of the material remains ferroelectric after the antiferroelectric–ferroelectric backward transition, which constitutes an additional contribution to polarization. Consequently, a higher domain wall density and mobility can be observed. Measurements after exposition to thermal treatment show that this ferroelectric response is metastable

Study of the long time relaxation of the weak ferroelectricity in PbZrO 3 antiferroelectric thin film using Positive Up Negative Down and First Order Reversal Curves measurements

International audienceThe weak ferroelectric contribution to the polarization of antiferroelectric lead zirconate (PZO) thin films has been investigated using PUND (Positive Up Negative Down) pulse measurements and hysterons decomposition by First Order Reversal Curves (FORC) technique. The PUND allows decomposing the measured current, obtained from the polarization-electric field loop measurements, into a switching and a non-switching contribution. We show that the weak ferroelectric phase is enhanced when a large electric field has been previously applied to the material, in order to switch from the antiferroelectric to the ferroelectric phase. Using the PUND measurement at fields below the antiferroelectric to ferroelectric phase transition, the polarization loop corresponding only to the ferroelectric switching contribution has been determined revealing that this contribution to the overall polarization is small. FORC measurements, however, indicate that the ferroelectric phase is present at different fields. At low fields, a quite homogeneous distribution of hysterons exists and at large field, a high concentration of hysterons at a field near to the antiferroelectric to ferroelectric phase transition can be seen. Moreover, when changing the delay between pulses of the PUND and the FORC measurements, we show that this weak ferroelectricity contribution is metastable and decreases with time

Dielectric, piezoelectric and electrostrictive properties of antiferroelectric lead-zirconate thin films

International audienc

Evidence of residual ferroelectric contribution in antiferroelectric lead-zirconate thin films by first-order reversal curves

International audienceIn this study, two different methods have been used in order to characterize leadzirconate anti-ferroelectric thin film elaborated by a modified sol-gel process: First-Order Reversal Curves (FORC) measurements and impedance spectroscopy coupled to hyperbolic law analysis. Approaches at low and high applied electric fields allow concluding on the presence of a weak residual ferroelectric behavior even if this contribution is not visible on the polarization-electric field loops. Moreover, the weak ferroelectric phase seems to switch only when the phase of the antiferroelectric cells is modified and no coalescence of ferroelectric domains at low field occurs due to a well distribution of small residual ferroelectric clusters in the material. The main goal of this paper is to show that FORC distribution measurements and impedance spectroscopy coupled to the hyperbolic law analysis are very sensitive and complementary methods

Influence du mode de frittage sur les propriétés de KNN : de la piézoélectricité à la thermoélectricité

National audience(K0.5Na0.5)NbO3 (KNN) est un composé blanc qui présente une structure pérovskite [1]. Il est très étudié comme matériaux piézoélectrique sans plomb depuis que Saito et al. [2] ont rapporté des valeurs importantes de d33 en 2004. Toutefois, il est difficile d’obtenir des céramiques denses de KNN par frittage conventionnel (environ 1100°C) du fait de la volatilisation des alcalins et/ou de la formation de phases secondaires [3]. L’utilisation du SPS (920°C- 50 Mpa-5 min) permet d’obtenir des céramiques denses, de couleur noire, avec une densité relative supérieure à 96 % [3]. La couleur noire des céramiques est due à une non-stœchiométrie en oxygène. Ces céramiques présentent des pertes électriques élevées. Un recuit de 5 heures à 900°C sous air permet de restaurer la couleur blanche des céramiques et d’atteindre les meilleures propriétés piézoélectriques (kp = 48 % et kt = 45 %) rapportées pour des céramiques de KNN non dopées.Les céramiques noires obtenues à l’issue du frittage par SPS présentent quand à elles des propriétés thermoélectriques de type n prometteuses [4]. La conductivité électrique n’est que d’environ 102 S/m mais le coefficient de Seebeck est élevé (-(600-700) µV/K). La propriété la plus remarquable comparativement à la pérovskite de référence SrTiO3 [5], est la conductivité thermique qui est basse et stable entre 325 et 1000 K entre 3.5 et 4 Wm-1K-1 (de 10 et 6 Wm-1K-1 pour SrTiO3). Ces propriétés prometteuses nécessitent maintenant d’être optimisées par un contrôle de la non-stœchiométrie en oxygène, par des substitutions aussi bien sur les sites alcalins que sur le site du niobium et par nanostructuration.Références[1] B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic Press (1971) London.[2] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Lead-free piezoceramics, Nature 432 (2004)84-87.[3] M. Bah, F. Giovannelli, F. Schoenstein, G. Feuillard, E. Le Clezio, I. Monot-Laffez, High electromechanical performance with spark plasma sintering of undoped K0.5Na0.5NbO3 ceramics, Ceramics International 40 (2014) 7473-7480.[4] F. Delorme, M. Bah, F. Schoenstein, F. Jean, M. Zouaoui Jabli, I. Monot-Laffez, F. Giovannelli, Thermoelectric properties of oxygen deficient (K0.5Na0.5)NbO3-x ceramics, Materials Letters 162 (2016) 24-27.[5] S.R. Popuri, A.J.M. Scott, R.A. Downie, M.A. Hall, E. Suard, R. Decourt, M. Pollet and J-W.G. Bos, Glass-like thermal conductivity in SrTiO3 thermoelectrics induced by A-site vacancies, RSC Advances 4 (2014) 33720-33723.Céramique, Frittage, SPS, Piézoélectricité, Thermoélectricité, (K0.5Na0.5)NbO3