Multiphase Coexistence and High Energy Storage Performance in BKT-Based Lead-Free Relaxor Ferroelectric Ceramics

Dielectric ceramic capacitors play a crucial role in energy electricity and electronic circuit systems owing to their exceptional ability to rapidly store and release electrical charge and remarkable power density. However, they still face critical challenges related to improving recoverable energy storage density (Wrec) and efficiency (η) synergistically. To address these issues, a novel relaxor ceramic system is designed in this work by introducing linear dielectric SrTiO3 (ST) into ferroelectric Bi0.5K0.5TiO3-BiFeO3 (BKT-BF) with large polarization. XRD refinement and TEM characterization demonstrate the coexistence of Rhombohedral (R3mr), Tetragonal (P4mm) and Cubic (Pm-3m) phases, which induces polar nano-regions (PNRs) in the ceramic and gives rise a decreased remanent polarization (Pr) and an enhanced η. SEM and ultraviolet–visible spectrum confirm a decreased grain size and a widened bandgap, leading to an ultra-high breakdown electric field. Therefore, a superior recoverable Wrec of 7.32 J/cm3 and an impressive η of 88.06% are achieved, accompanied by prominent stability across a wide temperature range (30-150 ℃), various frequencies (1-500 Hz), and a substantial number of cycles (1-105 cycles) in the BKT-BF-0.4ST sample. These findings strongly suggest that the BKT-BF-xST ceramic system holds exceptional promise for applications in pulse power capacitor applications.