Electrocaloric effect in (Na_0.5Bi_0.5)TiO₃-BaTiO₃-Bi(Mg_0.5Ti_0.5)O₃ relaxor ceramics.

Cooling technology based on the electrocaloric effect (ECE) is attracting considerable interest as an environmentally-friendly alternative to classical gas-compression based refrigerators and air conditioners. The electrocaloric effect consists in changing the lattice entropy (temperature) under the action of an external electric field applied adiabatically. Therefore, materials with inherent polar disorder, such as relaxor ferroelectrics, are considered promising for achivieng high ECE values. In this presentation, we report direct and indirect measurements of the electrocaloric effect in (y-1)[xBaTiO₃ – (1-x)(Na_0.5Bi_0.5)TiO₃] – (y)Bi(Mg_0.5Ti_0.5)O₃ (BT-NBT-BMT), x = 0.5, 0.1, 0.2 and y = 0, 0.1, 0.2. Ceramic samples were prepared using the solid-state synthesis method. The effect of the BMT additive on the structural, ferroelectric, and electrocaloric properties has been studied. We found that the addition of BMT to NBT-BT compounds promotes antiferroelectric relaxor behavior, manifested in slim double hysteresis loops. The electrocaloric effect was directly measured using a quasi-adiabatic calorimeter. The obtained data were compared with the ECE values indirectly estimated from the polarization hysteresis loops using the Maxwell relation. The effect of the crossover from ferroelectric to antiferroelectric relaxor behavior in the BT-NBT-BMT system on the ECE is discussed.