Electrocaloric Effect in Sodium Bismuth Titanate Based Ferroelectric Composites

Abstract

Perovskite ferroelectric materials exhibit electrocaloric effect (ECE) which is associated with entropy change in the material during application or removal of field. This electrocaloric effect is used for ferroelectric refrigeration. Commonly, the change of entropy between lowtemperature ferroelectric phase with ordered dipoles and high-temperature paraelectric phase without ordered dipoles is involved in ECE process and remarkable ECE always occurs near Curie temperature. The dipole-ordered state can be enhanced by decreasing temperature or enhancing applied electric field. Hence, the entropy drops and the ferroelectric material releases heat during application of field, while the entropy rises, and the material absorbs heat during withdrawal of field. Relaxor ferroelectrics could be attractive for ECE applications [1-4]. NBT is a promising candidate for ferroelectric and piezoelectric applications. It belongs to perovskite family. It undergoes various structural as well as phase transitions at different temperatures [5]. Compositional modifications in NBT results better properties. Addition of SrTiO3 to NBT shows better ferroelectric and piezoelectric properties [6]. Several authors have studied the electrocaloric effect on NBT based solid solutions. Yang Bai et. al., [7] reported abnormal electrocaloric effect of Na0.5Bi0.5TiO3–BaTiO3 lead-free ferroelectric ceramics above room temperature. Harberg et. al., [8] studied the electrocaloric effect in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 solid solutions. There are several applications for this technology, but the most intuitive application would be to cool computer chips and devices by employing refrigeration cycle [9]. In view of this, an effort has been made to investigate the PE loops, electrocaloric behavior, entropy change and relative cooling power of (1-x)Na0.5Bi0.5TiO3+(x) SrTiO3 (NBT-ST) where x = 0.075, 0.125, 0.150, 0.200 samples and results of such an investigation are presented in this paper.