Temperature-stable direct current-biased energy storage in barium titanate-based lead-free ceramics via paraelectric engineering

Abstract

High-energy-density multi-layer ceramic capacitors are essential for high-density power converters. Lead-free barium titanate (BaTiO₃)-based ferroelectric ceramics are widely employed in low-voltage scenarios, owing to their high permittivity. However, the ferroelectric state reveals strong dielectric nonlinearity, which limits applications for high-density power converters working at high voltages. At the paraelectric state, the dielectric nonlinearity is significantly lower, which, however, only occurs at about 130°C or above. In this work, BaTiO₃ is modified with La(Zn_2/3Nb_1/3)O₃ to stabilize the paraelectric state within the operating temperature range through paraelectric engineering. The optimized 0.92BaTiO₃-0.08La(Zn_2/3Nb_1/3)O₃-1 wt.%SiO₂ ceramic exhibits excellent temperature stability, with a small energy density variation below 3% and high efficiency above 95% at a severe electric field of 200 kV/cm direct current (DC) superimposed with 50 kV/cm AC over a wide temperature range of 25–125°C. The high efficiency is related to the consistency between grain and grain boundary contributions from impedance analysis. The excellent temperature stability is elucidated by deconvolution of temperature-dependent current density-electric field curves, which specifies that the dominant linear contribution and minimal leakage current remain nearly unchanged against various temperatures at DC-biased electric fields. Moreover, the optimized ceramic demonstrates remarkable frequency stability in the range of 5–200 Hz and outstanding cycling reliability up to 10⁵ cycles, with the variation of discharged energy density less than 1% and 1.5%, respectively. The proposed paraelectric engineering paves a promising way for enhancing DC-biased energy storage with temperature stability in lead-free ferroelectrics towards high-density power converters.