Enhancing Comprehensive Energy Storage Properties in Tungsten Bronze Sr_0.53Ba_0.47Nb₂O₆-Based Lead-free Ceramics by B-Site Doping and Relaxor Tuning

Abstract

Dielectric ceramics with relaxor characteristics are promising candidates to meet the demand for capacitors of next-generation pulse devices. Herein, a lead-free Sb-modified (Sr_0.515Ba_0.47Gd_0.01) (Nb_1.9-<i>x</i>Ta_0.1Sb_<i>x</i>)O₆ (SBGNT-based) tungsten bronze ceramic is designed and fabricated for high-density energy storage capacitors. Using a B-site engineering strategy to enhance the relaxor characteristics, Sb incorporation could induce the structural distortion of the polar unit BO₆ and order-disorder distribution of B-site cations as well as the modulation of polarization in the SBGNT-based tungsten bronze ceramic. More importantly, benefiting from the effective inhibition of abnormal growth of non-equiaxed grains, Sb introduction into SBGNT-based ceramics could effectively suppress the conductivity and leakage current density, enhancing the breakdown strength, as proved by the electrical impedance spectra. Consequently, a remarkable comprehensive performance via balancing recoverable energy density (∼3.26 J/cm³) and efficiency (91.95%) is realized simultaneously at 380 kV/cm, which surpasses that of the pristine sample without the Sb dopant (2.75 J/cm³ and 80.5%, respectively). The corresponding ceramics display superior stability in terms of fatigue (10⁵ cycles), frequency (1∼200 Hz), and temperature (20∼140 °C). Further charge-discharge analysis indicates that a high power density (89.57 MW/cm³) and an impressive current density (1194.27 A/cm²) at 150 kV/cm are achieved simultaneously. All of the results demonstrate that the tungsten bronze relaxors are indeed gratifying lead-free candidate materials for dielectric energy storage applications.