Coupled Microstructural and Phase Evolution in Doped Relaxor Ceramics for High-Efficiency, Fatigue-Resistant Dielectric Energy Storage

The ability to control the interplay between lattice symmetry, local polar order, and microstructural length scales is critical for advancing high-performance dielectric energy-storage materials. Here, we demonstrate that A-site Sr substitution in Ba1-xSrxTi0.90Zr0.10O3 (0 ≤ x ≤ 0.30) enables a direct coupling between microstructural refinement and polymorphic phase evolution, providing an effective pathway to tune relaxor behaviour and energy-storage performance. Comprehensive structural and spectroscopic analyses (Rietveld-refined X-ray diffraction, Raman phonon dynamics, and dielectric dispersion) reveal a systematic phase evolution from a tetragonal ferroelectric state (BZT) to orthorhombic–tetragonal coexistence (BSZT-10), and ultimately to a pseudo-cubic relaxor state (BSZT-30). This transition is accompanied by pronounced grain refinement (from 1.42 µm to 0.42 µm) and a progressive shift of the dielectric maximum temperature (Tₘ) toward room temperature, indicating enhanced polar disorder and relaxor characteristics. These coupled structural and microstructural modifications result in progressively slimmer polarization–electric field (P–E) loops, yielding high recoverable energy densities of 199.6 mJ.cm−3 (BZT) and 180.0 mJ.cm−3 (BSZT-10) at 50kV/cm. At higher Sr content, the emergence of a pseudo-cubic relaxor state suppresses remanent polarization, leading to an ultrahigh energy-storage efficiency of ~99% in BSZT-30. Importantly, all compositions exhibit excellent operational stability, with <5% variation in recoverable energy density over 25-120 °C, efficiencies exceeding 85% across 30-120 Hz, and fatigue endurance beyond 106 charge-discharge cycles without degradation. These results establish Sr-driven coupling between phase symmetry and microstructure as a robust design strategy to balance energy density, efficiency, and long-term reliability in relaxor ferroelectric ceramics, providing new insights for the development of next-generation dielectric capacitors.