Electrocaloric Effect in (1−x)(0.8Na_0.5Bi_0.5TiO₃-0.2BaTiO₃)−xCaTiO₃ Solid Solutions at High Electric Fields

Abstract

Recently, promising results were obtained in studies of the electrocaloric effect in thin films. Therefore, research into this effect at high applied electric field values in bulk ferroelectrics is an important task for those scoping out materials that could be appropriate for cooling devices based on the electrocaloric effect. The present study addresses electrocaloric effect in (1−x)(0.8Na1/2Bi1/2TiO3-0.2BaTiO3)−xCaTiO3 solid solutions by the direct method in electric fields ranging from 0 up to 100 kV/cm and at temperatures of up to 150 °C. The choice of 0.8Na1/2Bi1/2TiO3-0.2BaTiO3 as the starting composition is motivated by high spontaneous polarization within the studied range of electric fields, while CaTiO3 is added to reduce depolarization temperature at, and below, room temperature. In the studied temperature range, the maximal value of electrocaloric effect with temperature change of ΔT = 1.0 °C was found in the composition with x = 0.050 at 100 °C, having significant contribution from the entropy jump at the first-order phase transition induced by an electric field. At increasing CaTiO3 concentration, the attainable ΔT decreases. Measurements of polarization current, which were taken simultaneously with ΔT measurements, allowed us to study differences between ΔT obtained by the direct and the indirect methods.

Keywords

• sodium bismuth titanate
• solid solutions
• electrocaloric effect
• dielectric polarization
• phase transitions
• Maxwell relation