Nonstoichiometric effect on electrocaloric, pyroelectric and energy storage properties of 0.94NaxBiyTiO3–0.06BaTiO3 bulk ceramics

Abstract

The effect of nonstoichiometry on the pyroelectric, electrocaloric and energy storage properties in 0.94NaxBiyTiO3–0.06BaTiO3 (y = 0.49, 0.50, 0.51: x = 0.50 and y = 0.50: x = 0.51) bulk ceramics is investigated. The depolarization temperature and ferroelectric-relaxor phase transition vary with stoichiometry. The electrocaloric temperature (∆T) and entropy (∆S) change were calculated by Maxwell relation at different temperatures and electric fields. The 0.94Na0.50Bi0.49TiO3–0.06BaTiO3 showed maximum ∆T and ∆S as 1.2 K and 1.9 J/kgK, respectively at room temperature and 5.5 MV/m. However, Bi sufficient or excess compositions have the large value of ∆T (0.76 K) and ∆S (0.96 J/kgK) in the higher temperature range ~ 397–426 K. The pyroelectric coefficient obtained for stoichiometric composition is 9.4 × 10−4 C/m2K and 87 × 10−4 C/m2K at room temperature and Td, which increases to 10.1 × 10−4 C/m2K and 105 × 10−4 C/m2K, respectively for nonstoichiometric sample. The various pyroelectric figures of merit are calculated for all compositions and found that results are comparable with the previously reported lead-free ceramics. The recoverable energy storage and efficiency are enhanced by 35% (428 to 579 kJ/m3) and 21% (45% to 66%), respectively, when a nonstoichiometric composition is used. Thus, nonstoichiometry is an effective tool to tune pyroelectric, electrocaloric and other properties for the required application. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.