A superparaelectric design with structure optimization enables superior energy-storage performances and stabilities in (Na0.5Bi0.5)TiO3-based ceramics

Abstract

Lead-free (Na_0.5Bi_0.5)TiO₃-based dielectric materials are promising for electrostatic energy storage due to their strong polarization response and environmental friendliness. However, challenges like high electric hysteresis loss (W_loss) and low electric breakdown strength (E_b) limit their recoverable energy density (W_rec) and energy conversion efficiency (η). A superparaelectric design with structure optimization has been proposed to overcome these restrictions. Based on this strategy, a series of (1 − x)(Na_0.3Bi_0.38Sr_0.28)TiO₃–xCa(Ta_0.2Ti_0.75)O₃ (abbreviated as (1 − x)NBST–xCTT; x = 0.0, 0.1, 0.2, 0.3, and 0.4) ceramics were fabricated. Their phase structure gradually evolves from the rhombohedral and tetragonal coexistence (R&T) to the tetragonal and cubic coexistence (T&C), accompanied by the increasing proportion of weakly coupled and highly dynamic polar structures. This behavior enables the establishment of a superparaelectric relaxor ferroelectric (SPE-RFE) state, reducing W_loss, enhancing η, and improving dielectric stability. The improved microstructure with refined grains boosted E_b, further contributing to excellent performances. Notably, the optimized 0.6NBST-0.4CTT SPE-RFE ceramic, with high E_b, large polarization difference (ΔP), and slight W_loss, delivered a large W_rec of 6.90 J cm⁻³ with a high η of 92.55% at 600 kV cm⁻¹, alongside excellent dielectric stability (−60 to 135 °C) following the EIA-X7R standard. Moreover, a high power density (∼125 MW cm⁻³) and an ultrafast charge–discharge rate (t_0.9 ∼ 33 ns) were realized at 300 kV cm⁻¹. Encouragingly, the 0.6NBST-0.4CTT SPE-RFE ceramic also exhibits excellent energy-storage/charge–discharge stabilities. These results highlight the promising potential of the 0.6NBST–0.4CTT SPE-RFE ceramic for electrostatic energy storage. They also confirm the effectiveness of this strategy and provide valuable guidance for advancing dielectric energy-storage materials/capacitors.