High Energy Storage Performance and Large Electrocaloric Response in Bi_0.5Na_0.5TiO₃–Ba(Zr_0.2Ti_0.8)O₃ Thin Films

With regard to the global energy crisis and environmental pollution, ferroelectric thin films with unique polarization behavior have garnered considerable attention for energy storage and electrocaloric refrigeration. Herein, a series of (1 - x)Bi_0.5Na_0.5TiO₃-xBa(Zr_0.2Ti_0.8)O₃ (x = 0.3-0.9; (1 - x)BNT-xBZT) films were fabricated on Pt(111)/Ti/SiO₂/Si substrates. Incorporating BZT can tune the polarization behavior and phase transition temperature of BNT. A high recoverable energy density ≈ 82 J cm^-3 and optimized efficiency ≈ 81% were realized for the (1 - x)BNT-xBZT thin film with x = 0.7. The thin film exhibits excellent stability in energy storage performance, a wide working frequency range (0.5-20 kHz), a broad operating temperature window (20-200 °C), and reduplicative switching cycles (10⁷ cycles). In addition, the 0.5BNT-0.5BZT film exhibits a desirable electrocaloric effect with a large adiabatic temperature change (ΔT ≈ -22.9 K) and isothermal entropy change (ΔS ≈ 33.4 J K^-1 kg^-1) near room temperature under a moderate applied electric field of 2319 kV cm^-1. These remarkable performances signify that the (1 - x)BNT-xBZT system is a promising multifunctional electronic material for energy storage and solid-state cooling applications.