Effect of HfO2 addition as intergranular grains on the energy storage behavior of Ca0.6Sr0.4TiO3 ceramics

Pore free Ca0.6Sr0.4TiO3 (CST) ceramics with HfO2 additives (0 wt.%, 2.0 wt.%, 4.0 wt.% and 6.0 wt.%) were fabricated via solid state reaction method at 1400 °C. Structure characterization was conducted by XRD and SEM, indicating the existence of HfO2 at grain boundaries as the intergranular phase. The dielectric breakdown strength and energy storage efficiency were found to be greatly enhanced for CST with moderate HfO2 additives, the sample with 4.0 wt.% HfO2 exhibited optimized microstructure and energy storage properties, with maximum average breakdown strength (28.9 kV/mm) and high energy storage efficiency (nearly 95% at 24 kV/mm). In addition, effect of Hf-rich intergranular phase on the charge transportation and interfacial polarization behavior was discussed. With good dispersion, the intergranular HfO2 phase was considered effective to modify the grain boundaries properties and consequently improve the energy storage performance for CST ceramics.