Impact of oxygen vacancy reduction on the dielectric, energy storage, and electrocaloric properties of annealed BCZT ceramic

Abstract

Through this study, we address the challenge of oxygen vacancy-induced performance degradation of lead-free Ba_0.98Ca_0.02Zr_0.07Ti_0.93O₃ (BCZT) ceramic. In particular, we focus on the role of post-sintering annealing in reducing oxygen vacancies and the ensuing enhancement in the functionalities of BCZT ceramics. BCZT ceramic was synthesized through the conventional solid-state reaction method, and post-sintering annealing was employed to mitigate the oxygen vacancies. The annealed compound revealed the coexistence of tetragonal and orthorhombic phases, which was confirmed through the refinement of the X-ray diffraction pattern and further supported by Raman spectroscopy. At the Curie temperature (T_C ∼ 93 °C) and 1 kHz frequency, BCZT ceramic displayed an exceptional dielectric constant of ∼14 685 and a low dielectric loss of 0.04. The annealed ceramic achieved a recoverable energy density (W_rec) of 195.91 mJ cm⁻³ with an outstanding energy efficiency of 91.20%, derived from the first quadrant of the ferroelectric hysteresis loop at T_c. Additionally, the ceramic showed an impressive value of ∼1450 pm V⁻¹ of the effective converse piezoelectric coefficient () under application of an electric field of 20 kV cm⁻¹. The electrocaloric properties revealed an adiabatic temperature change (ΔT) of 1.24 K and an isothermal entropy change (ΔS) of 1.36 J Kg⁻¹ K⁻¹ at T_c. These exceptional properties are attributed to the synergistic effects of the optimized c/a ratio, high density, and fewer oxygen vacancies achieved through post-sintering annealing.