Enhanced Electrocaloric Effect in Sr²⁺-Modified Lead-Free BaZr<i>_x</i>Ti_1–<i>x</i>O₃ Ceramics

Abstract

Barium strontium zirconate titanate ceramics ((BaSr)(ZrTi)O₃-BSZT) with Zr⁴⁺ ionic contents of 15 and 20 mol % and Sr²⁺ ionic contents of 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. X-ray diffraction and scanning electron microscopy were used to characterize the lattice structure and morphologies of the ceramics. Permittivity and polarization as a function of temperature were characterized using an impedance analyzer and a Tower-Sawyer circuit. The electrocaloric effect was measured directly and calculated using the Maxwell relation (indirectly). The results indicated that the BSZT ceramics change from a normal ferroelectric to a relaxor ferroelectric with increasing Zr⁴⁺ ionic content, which can be further modified by the addition of Sr²⁺ ionic content. The optimized adiabatic temperature change Δ T obtained is 2.43 K in (Ba_0.85Sr_0.15)(Zr_0.15Ti_0.75)O₃ ceramics, and Δ T >1.6 K over a wide temperature span of 120 °C was obtained.