Properties of 0.74BiNaTiO3-0.06SrTiO3 / Bi0.5(Na0.8K0.2)0.5TiO3 ceramic composite

We investigated the temperature- and frequency-dependent polarization and strain of two Bismuth-based perovskite composites. A matrix material was chosen as 0.74Bi_0.5Na_0.5TiO₃ -0.26SrTiO₃ (BNT-ST) which have a transition point of 60°C from relaxor to ferroelectric phase (T_R-F). An inclusion material was Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ (BNKT) possessing the T_R-F of 120°C. Depending on test temperature, the different polarization and strain behaviors were observed in BN-TST/BNKT composite. At T=25°C, the composite exhibited double-like polarization loop and parabolic strain curves which involve ergodic relaxor-to-normal ferroelectric phase transition with external electric field and the reverse ferroelectric-to relaxor phase transition with removal of the field. When T= 80°C, the BNT-ST/BNKT has very slim polarization and strain of which magnitude are slightly increased values from pure BNT-BT. When T= 120°C, both composites have slim polarization and strain behaviors of which values are almost same as the pure BNT-ST. These high field-induced polarization and strain with respect to temperature for the composites are related to the thermal stability of ferroelectric inclusions, and their nucleation and growth in relaxor matrix.