Electrocaloric and dielectric studies of lead-free BaTi1−x(Nb0.5Yb0.5)xO3 (x = 0.1, x = 0.125) ceramics

Abstract

The present work investigates the structural, dielectric, ferroelectric, Raman spectroscopy properties and electrocaloric effect in lead free BaTi1−x(Nb0.5Yb0.5)xO3 (BTNY) (x = 0.1 and x = 0.125) ceramics. The dielectric study indicated a relaxor behavior in both compositions that evolves in parallel with the increase of the x value. The relaxor behavior and the structural properties were confirmed by Raman spectroscopic measurement. The electrocaloric (EC) effect in the studied ceramics was carried out through the indirect method based on Maxwell equation. Both compositions presented a shift in the temperature of EC maximum (TEC), which rose from 7°C for x = 0.1–41°C for x = 0.125. These two compositions gave maximum EC temperature changes (ΔT) at above their Tm on application of a 5kV/cm electric field. These temperature changes are ΔT = 0.041K at TEC = 306K and ΔT = 0.053K at TEC = 282K for x = 0.1 and x = 0.125 respectively. Such values exceed significantly those found in other lead-free EC materials. At room temperature (RT), these compositions provided a very interesting EC coefficient (ξ = ΔT/ΔE) compared to the pure BaTiO3 (BT). These values lie between 0.08 and 0.1 Kmm/kV for ΔE = 5kV/cm, also greater than the values for some lead-based ferroelectrics.