Phase and Band Structure Engineering via Linear Additive in NBT-ST for Excellent Energy Storage Performance with Superior Thermal Stability

Abstract

Lead-free relaxor ferroelectric ceramics with ultrahigh energy-storage performance are vital for pulsed power systems. We herein propose a strategy of phase and band structure engineering for high-performance energy storage. To demonstrate the effectiveness of this strategy, (1 - <i>x</i>)(0.75Na_0.5Bi_0.5TiO₃-0.25SrTiO₃)-<i>x</i>CaTi_0.875Nb_0.1O₃ (NBT-ST-<i>x</i>CTN, <i>x</i> = 0.1, 0.2, 0.3, 0.4, and 0.5) samples were designed and fabricated via the solid-state reaction method. The linear dielectric CTN was used as a modulator to tune both phase and band structures of the tested system. Our results show that both rhombohedral phase (<i>R-</i>phase) and tetragonal phase (<i>T-</i>phase) coexist in the samples. The <i>R</i>/<i>T</i> ratio decreases, while the band gap increases with increasing CTN content. The best energy-storage properties with large energy storage density (<i>W</i>_rec = 7.13 J/cm³), a high efficiency (η = 90.3%), and an ultrafast discharge time (25 ns) were achieved in the NBT-ST-0.4CTN sample with <i>R</i>/<i>T</i> = 0.121. Importantly, along with its excellent energy-storage performance, the sample exhibited superior thermal stability with the variations of <i>W</i>_rec ≤ 7% and η ≤ 10% over the wide temperature range of 233-413 K. This work suggests that this engineering of phase and band structures is a promising strategy to achieve superior energy-storage properties in lead-free ceramics.