Bi(Mg0.5Hf0.5)O3-modified SrTiO3 lead-free ceramics for high-temperature energy storage capacitors

Lead-free (1 - x)SrTiO3-xBi(Mg0.5Hf0.5)O-3 (0.05 <= x <= 0.4) ceramics were prepared by high-temperature solid-state sintering method. The microstructure, dielectric properties, and energy storage performance were investigated. The diffused phase transition was observed in samples with x >= 0.1, showing typical relaxor characteristic. In particular, 0.8ST-0.2BMH composition exhibits stable dielectric permittivity with variation below 15% over temperature range of - 100 degrees C to 185 degrees C, superior to that of undoped SrTiO3. The calculated Weibull characteristic breakdown strength is 480 kV/cm for 0.8ST-0.2BMH ceramic, and a large energy density of 4.1 J/cm(3) with high energy efficiency of 92% is obtained at electric field of 470 kV/cm. Of particular significance is that the energy efficiency remains above 91% at elevated temperature of 180 degrees C. In addition, fast discharge time (similar to 0.88 mu s) with high-power density of 2.8 MW/cm(3) is achieved in 0.8ST-0.2BMH ceramic. All the above results indicate that the 0.8ST-0.2BMH relaxor dielectric is a promising lead-free ceramic for high-temperature energy storage applications.