Due to the continuous trend of miniaturization in microelectronics industry, the interest concerning scale dependent phenomena in ferroelectric materials attracted a broad interest in the last years. Apart the need to understand how to preserve the functional properties comparative to ones of bulk material when reducing the size down to nanoscale, there is also a specific interest concerning the maximization of dielectric, piezoelectric and ferroelectric properties at some specific grain size. Concerning this aspect, the researchers dedicated mainly to the critical grain size (GS) of BaTiO3 around 1 μm, for which enhanced dielectric, ferroelectric and piezoelectric properties have been always found, irrespective of the synthesis procedure and sintering method [1,2]. However, systematic studies to find a similar critical GS in other BaTiO3-based compounds have not been previously performed.
In this work, a series of dense BaTiO3-based ceramics (Ba0.85Ca0.15Ti0.90Zr0.10O3 and 5%Zr-BaTiO3) with grain size larger than 1μm and 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 1200-1500°C and times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 1 μm for the samples sintered at lower temperature and ~140 μm for higher sintering temperature. The structural characterization was performed for monitoring the effect of grain size and field on the phase composition in BaTiO3-based 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 μm) for which the remnant and saturation polarisation is 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 BaTiO3-based ceramics. The presented data provide a complete picture of the size effect dependence of functional properties in BaTiO3-based ceramics.