Enhanced Electrocaloric Effect in Sr²⁺-Modified Lead-Free BaZrₓTi₁–ₓO₃ Ceramics

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 ΔT obtained is 2.43 K in (Ba₀.₈₅Sr₀.₁₅)(Zr₀.₁₅Ti₀.₇₅)O₃ ceramics, and ΔT >1.6 K over a wide temperature span of 120 °C was obtained.