A synergistic two-step optimization design enables high capacitive energy storage in lead-free Sr0.7Bi0.2TiO3-based relaxor ferroelectric ceramics

Abstract

Dielectric ceramic capacitors are essential components in next-generation advanced pulse power systems owing to their ultrafast charging/discharging rate and high power density, nevertheless confronting critical challenges regarding the collaborative improvement of recoverable energy storage density (W_rec), efficiency (η), and temperature stability. Herein, a synergistic two-step optimization strategy on Sr_0.7Bi_0.2TiO₃ (SBT)-based relaxors is proposed to address the current issues, that is, induce the high activity and ultrafine polar nanoregions to generate low hysteresis and sustained large polarization via composition optimization, and then produce an ultrasmall grain size with compact grain boundaries to further improve the breakdown strength and Vickers hardness (H_v) by a two-step sintering process. A large W_rec (∼5.98 J cm⁻³) and an ultrahigh η (∼98.6%) at 580 kV cm⁻¹ are achieved simultaneously in SBT-based relaxor ferroelectrics accompanied by an ultrahigh H_v ≈ 8.38 Gpa, showing a large advance in comprehensive capacitive energy storage. Both W_rec and η also exhibit excellent stabilities at 420 kV cm⁻¹ over a wide temperature (30–140 °C) and frequency (1–200 Hz) range, together with a high power density of 187.4 MW cm⁻³ and ultrafast discharge speed of 36 ns. This work thus demonstrates competitive SBT-based lead-free relaxors and provides a paradigmatic avenue to construct high-performance dielectrics for advanced energy storage applications.