Grain size effect on the functional properties of BZT-BCT ceramics

One of the most promising BT-based materials for piezoelectric applications is the pseudobinary ferroelectric (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BCTZ) (x is the molar percent of BCT). In the present paper we present preparation and functional characterisation of 0.5Ba(Zr0.20Ti0.80)O3-0.5(Ba0.70Ca0.30)TiO3 (BZT-BCT) ceramics with grain size around 1 µm. The powders were prepared by the conventional solid-state route and calcined at 1000°C/4 hours. Dense ceramics (relative density above 94-98%) with different grain size were obtained by sintering the resulted powders at temperatures between 1400-1500°C for different times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2?m, for the samples sintered at 1400ºC/2h, to 27?m, for the samples obtained at 1500ºC /24h. The structural characterization was performed for monitoring the effect of grain size and field on the phase composition in BCTZ ceramics. The evolution of polar order and phase transitions with grain size has been studied using dielectric permittivity measurements at 20Hz- 2MHz between 25 and 150°C. Also, the piezoelectric properties at different poling conditions (poling temperature and electric field) were investigated and discussed according with ceramics grain size. Polarization vs. electric field (P-E) hysteresis loop study showed that exist a critical grain size (~ 9 ?m) for which the remnant and saturation polarisation is higher. The same critical size was obtained from dc-tunability investigation. In addition, we develop a mesoscale modelling (Monte Carlo with Finite Element Method calculations) to describe size effects on the low-field properties in BCTZ ceramics. The presented data provide a complete picture of the size effect dependence of functional properties in BZT-BCT ceramics. Acknowledgment: The financial support of the PN III-P1-1.1-TE-2016-1951 is acknowledged.