Temperature dependence of polarization and strain in Bi0.5Na0.5TiO3-SrTiO3 multilayer composites

Relaxor-ferroelectric phase transition materials exhibit excellent strain behavior under applied electric fields for utilization in actuator applications. However, the large strain of relaxor-ferroelectric phase transition materials can only be achieved in a narrow temperature range. Hence, in this study, composition-based multilayer samples and compositional gradient composite (CGC) samples were designed and fabricated to extend the usable temperature range of relaxor-ferroelectric materials. The raw materials used were 0.78(Bi0.5Na0.5TiO3)–0.22SrTiO3 and 0.72(Bi0.5Na0.5TiO3)–0.28SrTiO3. The multilayered sample containing two ceramics showed higher temperature-dependent strain and polarization than those of the single-composition ceramic. In addition, phase transition was observed in the CGC in the low- and high-temperature ranges. In the CGC sample, the compositional gradient characteristics of Sr were observed along the vertical direction owing to diffusion. This reduced the temperature-dependent unipolar strain of the sample (0.148–0.175%) in the range of −20 °C < T < 100 °C. This behavior can be attributed to the combined effect of the relaxor-ferroelectric phase transition and ferroelectric domain reorientation, as well as the relaxor electrostriction. The sintering temperature had a significant effect on the compositional gradient of Sr and the performance of the layered composites.