Electrocaloric effect in (1-x)(0.8Na_1/2Bi_1/2TiO₃-0.2BaTiO₃)-xCaTiO₃ solid solutions at high fields.

Recently, many efforts have been made to find high values of reversible electrocaloric effect (ECE) induced temperature change DT, which is the most important parameter for creation of ECE-based cooling systems. The application of larger electric fields has shown promise as a way of increasing DT. However, there are only a small number of publications where ECE is directly measured at electric fields in the range above 20-30 kV/cm. The present work provides a detailed overview of ECE in (1-x)(0.8Na_0.5Bi_0.5TiO₃-0.2BaTiO₃)-xCaTiO₃ (x=0.05-0.125) solid solutions. For these compositions, we have measured DT as a function of temperature and applied fields of up to 100 kV/cm using the direct measurement method. At lower concentrations of CaTiO₃, values of DT above the electric field-induced first order phase transition reach 1ºC with a large contribution from an entropy jump. At higher CaTiO₃ concentrations, the electric field-induced phase transition is suppressed. This causes an expressed reduction of DT, despite a moderate reduction of electric field-induced dielectric polarization. Furthermore, a comparison of the direct measurement method of ECE temperature change with the indirect one using Maxwell’s relations is presented. Here, an inconsistency between the results obtained by both methods is demonstrated and interpreted.

This work has been funded by the Latvia Science Council grant LZP-2020/2-0080.