Influence of K_0.5Bi_0.5TiO₃ on the structure, dielectric and ferroelectric properties of (Ba,Ca)(Zr,Ti)O₃ ceramics

A new lead-free ferroelectric solid solution between (Ba,Ca)(Zr,Ti)O₃ (BCZT) and K_0.5Bi_0.5TiO₃ (KBT) has been systematically investigated in terms of its phase transformations, microstructure, dielectric and ferroelectric properties. The incorporation of KBT into BCZT was found to enhance the sintering behavior,
although secondary phases of K₄Ti₃O₈ and BaBi₄Ti₄O₁₅ were detected at high KBT contents. Chemical heterogeneity was also observed in the form of core-shell grain structures comprising tetragonal ferroelectric BCZT-rich cores with pseudo-cubic relaxor ferroelectric KBT-rich shell regions. Temperature-dependent dielectric property measurements revealed that the BCZT-KBT ceramics exhibited both normal and relaxor ferroelectric behaviour simultaneously, associated directly with the coreshell structure. Ferroelectric hysteresis measurements indicated that the remanent polarisation and coercive field were strongly dependent on KBT content. In common with other lead-free relaxor ferroelectrics, increasing temperature led to the formation of constricted  polarisation-electric field hysteresis loops, indicating the occurrence of a reversible electric field-induced nanopolar to long-range ordered ferroelectric state.