Role of grain size on the structural and functional properties of (Ba,Ca)(Zr,Ti)O3 ceramics

(1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BCTZ) pseudobinary ferroelectric (x is the molar percent of BCT) is one of the most promising BT-based materials for piezoelectric applications. In this work, a series of dense Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics with grain size larger than 1?m with uniform grain-size distribution were successfully prepared by the conventional solid-state reaction, and the grain-size effects on the structural, dielectric, ferroelectric and piezoelectric properties were explored in their un-poled and poled states. The ceramics were obtained by sintering solid state powders at different temperatures between 1400-1500°C and times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2 ?m for the samples sintered at 1400 ºC/2h to 27 ?m for the samples obtained at 1500 ºC/24h. 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. The low and high field investigations (P(E) hysteresis loops and dc-tunability) showed that exist a critical grain size (~ 9 ?m) for which the properties are higher. 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 Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics. Acknowledgment: The financial support of the PN III-P1-1.1-TE-2016-1951 is acknowledged.