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

The effect of nonstoichiometry on the pyroelectric, electrocaloric and energy storage properties in 0.94Na(x)Bi(y)TiO(3)-0.06BaTiO(3) (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 (Delta T) and entropy (Delta S) change were calculated by Maxwell relation at different temperatures and electric fields. The 0.94Na(0.50)-Bi0.49TiO3-0.06BaTiO(3) showed maximum Delta T and Delta 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 Delta T (0.76 K) and Delta S (0.96 J/kgK) in the higher temperature range similar to 397-426 K. The pyroelectric coefficient obtained for stoichiometric composition is 9.4 x 10(-4) C/m(2)K and 87 x 10(-4) C/m(2)K at room temperature and T-d, which increases to 10.1 x 10(-4) C/m(2)K and 105 x 10(-4) C/m(2)K, 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/m(3)) 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.