Effect of Porosity on Functional Properties of Lead-Free Piezoelectric BaZr0.15Ti0.85O3 Porous Ceramics

The present paper reports the dependence of dielectric, ferroelectric and piezoelectric properties on the porosity level in BaZr0.15Ti0.85O3 ceramics with porosity from 5% to 21%. Microporosity with 0–3 connectivity has been produced using PMMA microspheres as a sacrificial template. The functional properties (dielectric, ferroelectric and piezoelectric effect) are mostly affected by the “dilution effect”: permittivity decreases by 40% when porosity increases by 21%, and Pmax decreases from 13 to 5 µC/cm2 while the Prem is in the range of (2–8) µC/cm2. However, the reduction of the zero-field permittivity and hysteretic behaviour of ε(E) while the tunability level is still high makes from porous ceramics interesting materials for tunability application

Scale-Dependent Dielectric Properties in BaZr0.05Ti0.95O3 Ceramics

In the present work, BaZr0.05Ti0.95O3 ceramics with grain sizes between 0.45 and 135 µm were prepared by solid-state reaction and classical sintering. The effect of grain size on dielectric properties was systematically explored, and it was found that dielectric permittivity reaches a maximum value for grain sizes between 1.5 and 10 µm and then rapidly drops for larger grain sizes. A numerical finite element method was employed to eliminate the effect of porosity on the effective values of permittivity. The results indicate that it is possible to have a critical size in slightly doped barium titanate ceramics with enhanced functional properties for a grain size between 1.5 and 10 µm

Role of Density and Grain Size on the Electrocaloric Effect in Ba_0.90Ca_0.10TiO₃ Ceramics

Pure perovskite Ba0.90Ca0.10TiO3 ceramics, with a relative density of between 79 and 98% and grain sizes larger than 1 µm, were prepared by solid-state reaction. The dielectric and electrocaloric properties were investigated and discussed considering the density and grain size of the samples. Room temperature impedance measurements show good dielectric properties for all ceramics with relative permittivity between 800 and 1100 and losses of sat = 7.2 µC/cm2 to Psat = 16 µC/cm2). The largest electrocaloric effect was 1.67 K for ceramic with GS = 3 µm at 363 K and electrocaloric responsivity (ζ) was 0.56 K mm/kV. These values are larger than in the case of other similar materials; thus, Ba0.90Ca0.10TiO3 ceramics with a density larger than 90% and grain sizes of a few µms are suitable materials for electrocaloric devices

Sotiras

National audienceLa première campagne de fouilles de Sotiras (Nord-Ouest de l’île de Tasos) s’est déroulée du 19 juin au 10 juillet 2013, dans le cadre d’un programme de recherche associant l’École française d’Athènes à l’université de Bucarest. Les données préliminaires dont nous disposions au terme de la campagne topographique de 2012 nous avaient amenés à envisager la présence d’un atelier de production amphorique, et à nous fixer deux objectifs : 1) définir la chronologie générale du site en pratiquant des sondages ; 2) étudier le plateau surplombant le village de Sotiras, où apparaissaient le supposé four et un mur apparemment antique délimitant la zone à l’angle Sud-Ouest

Optimization of Processing Steps for Superior Functional Properties of (Ba, Ca)(Zr, Ti)O₃ Ceramics

Lead-free piezoelectric ceramics with nominal composition at morphotropic phase boundary Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZ) prepared by different processing routes and sintered either by conventional solid-state reaction or by spark plasma sintering (SPS) techniques were comparatively investigated to observe the role of structural modifications and of microstructures on the dielectric, ferroelectric, piezoelectric and electrocaloric responses. The ceramics presented relative densities from 75% to 97% and showed variations in their phase composition as a result of variable mixing and different synthesis and sintering parameters providing local compositional heterogeneity. As result, all of the ceramics showed diffuse phase transition and ferroelectric switching responses, with parameters affected mostly by density (Pr between 3.6 to 10.1 μC/cm2). High values for the electrocaloric response in the Curie range were found for the ceramics with predominantly orthorhombic character. Field-induced structural modifications were probed by tunability anomalies and by XRD experiments in remanence conditions. Piezoelectric effects with notably high figure of merit values were assigned to the better densification and poling efficiency of BCTZ ceramics