Direct measurement and dynamic mechanical analysis on the coexistence of positive and negative electrocaloric effects in Bi_0.5Na_0.5TiO₃-xBaTiO₃ solid solutions

Abnormal electrocaloric effect (ECE) is investigated in (1-x)Bi_0.5Na_0.5TiO₃-xBaTiO₃ solid solutions by calorimetry measurements, manifesting itself by the differences in the heats released and absorbed under the application and withdrawal of electric fields, respectively. The abnormal ECE is explained by the coexistence of positive and negative ECEs close to the ferroelectric-to-antiferroelectric transition temperature, which is demonstrated by the structural and ferroelectric properties determined from dynamic mechanical analyses and thermodynamics calculations on the solid solutions under an applied electric field, respectively. A threshold electric field below which the negative ECE occurs is obtained, in comparisons with that predicted by the thermodynamics Maxwell's relations. The abnormal ECE obtained from direct measurement is compared with that calculated by the indirect measurement, and the discrepancy is discussed.