Giant electrocaloric response over a broad temperature range in modified BaTiO₃ Ceramics

A giant electrocaloric effect (ECE) near room temperature is reported in a lead-free bulk inorganic material. By tuning Ba(Zr_xTi _1-x)O₃ compositions which also exhibit relaxor ferroelectric response to near the invariant critical point, the Ba(Zr _xTi_1-x)O₃ bulk ceramics at x ∼ 0.2 exhibit a large adiabatic temperature drop of 4.5 K, a large isothermal entropy change of 8 J kg^-1 K^-1, and a large EC coefficient (|ΔT_c/ΔE| = 0.52 × 10^-6 KmV^-1 and ΔS/ΔE = 0.93 × 10^-6 J m kg^-1 K ^-1 V^-1) over a 30 K temperature range. These properties added together indicate a general solution of the electrocaloric materials with high performance for practical cooling applications. A giant electrocaloric effect (ECE), i.e., a large adiabatic temperature drop (ΔT_c) with a high electrocaloric coefficient (ΔT_c/ΔE), is demonstrated in a modified lead-free ferroelectric ceramic, BaTiO₃, over a broad temperature range near the invariant critical point (ICP). Multiphase coexistence near ICP provides a larger entropy change compared with that of a pure ferroelectric-paraelectric transition. When coupled with the relaxor behavior, this leads to the observed giant ECE in BZT (x = 0.2) over a broad temperature range