Paraelectric Matrix-Tuned Energy Storage in BiFeO₃–BaTiO₃–SrTiO₃ Relaxor Ferroelectrics

Incorporation of polymorphic ferroelectric nanodomains into a paraelectric matrix has been proven to be effective to achieve high energy storage density in a relaxor ferroelectric system. In this work, we fabricated short-range ordered polymorphic 0.20BiFeO₃–(0.80 – <i>x</i>)­BaTiO₃ nanodomains in a paraelectric <i>x</i>SrTiO₃ host (0.40 ≤ <i>x</i> ≤ 0.65) to form ternary relaxors with transition temperatures in the range of 425–460 °C. The addition of SrTiO₃ suppresses the <i>P</i>–<i>E</i> loops of the binary BiFeO₃–BaTiO₃ system and improves the recoverable energy and energy storage efficiency. A well-sintered solid solution exhibits nearly ideal relaxor ferroelectric behavior for <i>x</i> = 0.50, which demonstrates the highest tetrahedral <i>c</i>/<i>a</i> ratio (1.0042), saturation polarization (26.39 μC/cm²), breakdown strength (183.1 kV/cm), and recoverable energy (2.15 J/cm³ at 190 kV/cm) and also shows high current density, high power density, and short discharge time. The overall evolution of the <i>c</i>/<i>a</i> ratio, saturation polarization, and recoverable energy follows an <i>x</i>-dependent volcanic shape, while the variation of residual polarization is <i>x</i>-independent. The maximum energy storage efficiency of 95.56% is observed for <i>x</i> = 0.55 at 200 kV/cm. These findings suggested that the 0.20BiFeO₃–(0.80 – <i>x</i>)­BaTiO₃–<i>x</i>SrTiO₃ system is promising for dielectric energy storage applications.