Design for high energy storage density and temperature-insensitive lead-free antiferroelectric ceramics

Dielectric capacitors with high power density and excellent temperature stability are highly demanded in pulsed power systems. AgNbO3-based lead-free antiferroelectric ceramics have been proven to be a promising candidate for energy storage applications. Nevertheless, the recoverable energy storage density (Wrec) still needs to be further improved to meet the requirements of the miniaturization and integration of pulsed power systems. In order to significantly increase Wrec, a strategy, by introducing A-site vacancies, stabilizing antiferroelectricity and decreasing the grain size, is proposed in this work. Here, Ag1−2xCaxNbO3 solid solutions were designed for achieving high maximum polarization (Pmax), large antiferroelectric–ferroelectric electric field (EF) and high breakdown electric field (Eb). A high Pmax of 39.6 μC cm−2, a large EF of 179 kV cm−1 and an Eb of 220 kV cm−1 were achieved in Ag0.92Ca0.04NbO3 ceramics, leading to an ultrahigh Wrec of 3.55 J cm−3. The significantly improved Wrec is about 2 times as high as that of the pure AgNbO3 counterpart. Meanwhile, the Ag0.92Ca0.04NbO3 ceramics exhibited temperature-insensitive Wrec with minimal variation less than 1.5% from room temperature up to 100 °C. A Ginzburg–Landau–Devonshire (GLD) phenomenology was proposed to reveal the increased stability of antiferroelectricity and the temperature-insensitive Wrec, which suggested that they are closely associated with the tailoring of free energy barriers for antiferroelectric–ferroelectric phase transition. The excellent energy storage performance makes the Ag1−2xCaxNbO3 system a good candidate for advanced pulsed power capacitors. More importantly, our findings open a new way for developing high performance AgNbO3-based and other lead-free systems for energy storage.