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

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 similar to 65 degrees C, from the relaxor to the ferroelectric phase (TR_F). The seed material was Bi-0.5(Na0.8K0.2)(0.5)TiO3 (BNKT), which possesses a TR-F of 120 degrees C. Different polarization and strain behaviors were observed in the BNT-ST/BNKT composite at different test temperatures. At T=25 degrees C (< TR-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 1=80 and 100 degrees C (> TR-F f the relaxor BNT-ST and < TR-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 degrees C (similar to TR-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. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.