Role of polar nanoregions in the enhancement of the recoverable energy storage density and electrostrictive coefficient in the lead free Na0.25K0.25Bi0.5TiO3

Abstract

The electrostrictive materials are gaining attention for the actuating application because of their positive strain irrespective to the electric field direction and low hysteresis loss. In this work, the room temperature electrostrictive effect of lead free ferroelectrics Na0.3K0.2Bi0.5TiO3 and Na0.25K0.25Bi0.5TiO3 are studied. Due to the relaxor nature of Na0.25K0.25Bi0.5TiO3, sprout shape strain (S) and pinched polarization (P) loops are noticed as a function of electric field (E), which are beneficial for high electrostrictive coefficient and recoverable energy storage density, respectively. The reversible transformation of the polar nanoregion into the ferroelectric domain with electric field is the reason behind the sprout shape S-E loop. This composition shows the dielectric constant of ≈4000 and strain of 0.30% without any Sneg (negative value of strain). The obtained value of the electrostrictive coefficient from the S vs. P2 graph of Na0.25K0.25Bi0.5TiO3 is ≈0.022 m4/C2, which is comparable to 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 composition and other Na0.5−xKxBi0.5TiO3-based binary solid solutions.