Excellent Electrocaloric and Energy Storage Capabilities in (Na0.8K0.2)0.5Bi0.5TiO3 Ceramic AITranslate

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DOI：https://doi.org/10.1021/acsaelm.3c01063

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A temperature-dependent polarization switching study reveals a normal ferroelectric P–E loop to an antiferroelectric double hysteresis loop in the vicinity of depolarization temperature (400 K, Td), which is believed to show a strong electrocaloric effect (ECE) and electrical energy-storage density (Wrec) in (Na0.8K0.2)0.5Bi0.5TiO3 (NKBT) ceramic when measured by an indirect method. Structural analysis using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy studies confirmed the coexistence of tetragonal (P4mm) and rhombohedral (R3c) phases. A temperature-dependent dielectric study has revealed a frequency dispersion around 400 K, which hints at the presence of a frustrated interaction resulting in the slowing down of polar domain dynamics below a diffuse phase transition. The high value of ECE in the lead-free NKBT ceramic is also investigated by a direct method, confirming the multifunctional nature of NKBT and its usefulness for applications in refrigeration and energy storage. A direct method of electrocaloric (EC) measurement in NKBT ceramic exhibits an adiabatic temperature change (ΔT) ∼ 1.10 K and an EC strength (ξ) ∼ 0.55 Kmm/kV near Td at an externally applied field of 20 kV/cm, which is consistent with the literature. The recoverable energy (Wrec) ∼ 0.78 J/cm3 and electrical storage efficiency (η) ∼ 86% are also observed near Td when an applied field of 20 kV/cm is switched at 1 Hz. This behavior is ascribed to the delicate balance between the field-induced normal ferroelectric–antiferroelectric transition and the thermal energy needed to disrupt the frustrated interaction.