Lead-free (Sr0.7Ca0.3)1−1.5xBixTiO3 ceramics with temperature stable energy storage density and discharge efficiency for pulsed power technology

Abstract

• Homogeneous phase transition restricts the abrupt variation of polarization. • Reduction of oxygen vacancy concentration improves the breakdown strength. • The activation and ordered arrangement of PNRs enhance the polarization. Lead-free energy storage ceramics have attracted a large concentration for their significant role in pulsed power technology. Here, environmentally friendly (Sr 0.7 Ca 0.3 ) 1−1.5x Bi x TiO 3 relaxor ferroelectric ceramics are systematically studied. The introduction of Bi 2 O 3 can enhance polarization. As the Bi 2 O 3 content increases, the dielectric constant rises from 300 to 774, while the dielectric loss is less than 0.5% under a measurement frequency of 1 kHz. For the Sr 0.49 Ca 0.21 Bi 0.2 TiO 3 ceramic, an energy storage density ( W ) of 2.035 J cm −3 and a high energy storage efficiency ( η ) of 91.84% achieved under an electric field of 260 kV cm −1 . The variation rate of the dielectric constant is less than 15% (compared with the capacitance at 25 °C) in the temperature range of − 55–125 °C, meeting the requirement of the EIA X7R specification, and the W and discharge energy density ( W d ) also exhibit desirable temperature stability in the temperature range of 30 °C to 150 °C. These results are related to the homogeneous phase transition and low concentration of oxygen vacancies. The thermal activation of polar nanoregions ( PNRs ) partially compensates for the reduction of polarization caused by lattice expansion, which also contributes to the temperature stability. Taken together, the results of this study indicate the Sr 0.49 Ca 0.21 Bi 0.2 TiO 3 ceramics have potential as a target for developing high energy storage lead-free ceramic capacitors.