Ultrawide bandgap CaHfO3 as a linear dielectric filler for superior energy storage in 0.7Bi0.5Na0.5TiO3-0.3Sr0.7Nd0.2TiO3 ceramics

Abstract

High-power pulsed electronics and compact capacitive storage demand lead-free dielectrics that simultaneously offer high breakdown strength (BDS), energy storage density (W_rec), energy efficiency (η) and stability across frequencies and temperatures. Guided by an ultrawide bandgap assisted design, we incorporate an ultrawide bandgap (∼6 eV) linear dielectric, CaHfO₃ (CH), into 0.7Bi_0.5Na_0.5TiO₃-0.3Sr_0.7Nd_0.2TiO₃ (BNT-0.3SNT) to elevate BDS while minimally perturbing the host lattice. Moreover, the high-strength, covalent character of octahedrally coordinated Hf–O bonds is central to stability. BNT-0.3SNT delivers a W_rec of 4.37 J cm⁻³, whereas the optimized BNT-0.3SNT-0.05CH achieves a BDS of up to 700 kV cm⁻¹, with a W_rec of 8.61 J cm⁻³ and an η of 83.2%. Moreover, it exhibits excellent frequency stability, with the W_rec varying by only 3.6% over 0.1–200 Hz. Mechanistically, the similarity in ionic radii and valence states between CH and the host matrix helps preserve high saturation polarization; concurrently, grain refinement, bandgap widening, and a reduced oxygen-vacancy concentration act synergistically to enhance the BDS and W_rec. This ultrawide bandgap strategy provides a general design route to high field, fast charge–discharge, lead-free energy storage ceramics for next generation pulsed power systems.