Calcination Temperature-Associated Discontinuous Grain Size Effect on Electrocaloric Properties in Fine-/Large-grain BaTiO3-based Ferroelectric Ceramics

Influences of calcination temperature (T-cal) on discontinuous grain growth (DGG), and related grain size effect on structure/ferroelectric/electrocaloric properties were studied and compared in fine-/large-grain Ba(Ti0.85Zr0.15)O-3 ceramics. DGG phenomena from several to >100 mu m are all observed with rising sintering temperature (T-S). Increasing T-cal (1200-1320 degrees C) can cause larger powders but decrease the sintering activity, leading to a higher critical T-S (1320-1360 degrees C) of DGG. Relatively high T-cal (larger powder size) will lead to smaller ceramic grains and density before DGG, while being prone to obtain larger grains and stronger ferroelectric correlations, but lower density after DGG. The over-sized powders and smaller grains/density will present in ceramics if T-cal closes to critical T-S. In fine- and large-grain ceramics, grain size variation is similar to the evolution of dielectric, ferroelectric polarization, and electrocaloric properties, but shows an opposite variation trend with coercive field and relaxor phase transition. Electrocaloric strength of fine-grain ceramics increases with a rising electric field due to their difficult domain switching, while an opposite trend shows in large-grain ceramics. Finally, higher electrocaloric properties are obtained in ceramics with relatively big grains because of easier polarization rotation, higher polarization, and polarization change rate.