Polarization and strain behaviors of 0.74BiNaTiO3–0.26SrTiO3/Bi0.5(Na0.8K0.2)0.5TiO3 ceramic composite

Abstract We investigated the temperature- and frequency-dependent polarization and strain of two bismuth-based perovskite materials, a matrix material and a seed material, with which we formed a composite whose properties we likewise investigated. The chosen matrix material is 0.74Bi 0.5 Na 0.5 TiO 3 –0.26SrTiO 3 (BNT-ST) which has a transition point of ~65 °C, from the relaxor to the ferroelectric phase (T R-F ). The seed material was Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 (BNKT), which possesses a T R-F of 120 °C. Different polarization and strain behaviors were observed in the BNT-ST/BNKT composite at different test temperatures. At T=25 °C ( R-F of the relaxor BNT-ST), the composite exhibited a hysteretic polarization loop and parabolic strain curves which involve an ergodic relaxor-to-normal ferroelectric phase transition with application of an external electric field and the reverse ferroelectric-to relaxor phase transition with removal of the field. When T=80 and 100 °C (>T R-F °f the relaxor BNT-ST and R-F of the ferroelectric BNKT), the BNT-ST/BNKT has a slim polarization loop and strain magnitudes that are slightly increased from those of pure BNT-ST. When T=120 °C (~T R-F of the ferroelectric BNKT), the composite has a very slim polarization loop and strain behavior with values that are almost same as those of pure BNT-ST. In addition, the P-S relation for the BNT-ST/BNKT is identical to that of BNT-ST as the operating frequency increases up to 100 Hz. This may be because the polarization of BNT-ST is lower than that of BNKT. The electric field-induced polarization and strain of the BNT-ST/BNKT composite with respect to the temperature and frequency are related to the thermal stability of the ferroelectric seed and the degree of the phase transition in the relaxor matrix.