Superior Thermal Stability of High Energy Density and Power Density in Domain-Engineered Bi_0.5Na_0.5TiO₃–NaTaO₃ Relaxor Ferroelectrics

Abstract

Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 - <i>x</i>)Bi_0.5Na_0.5TiO₃-<i>x</i>NaTaO₃ [(1 - <i>x</i>)BNT-<i>x</i>NT, <i>x</i> = 0-0.30] lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The <i>x</i> = 0.20 ceramic exhibits superior thermal stability of discharged energy density (<i>W</i>_D) with a variation of less than 10% in an ultrawide temperature range of -50 to 300 °C, showing a significant advantage compared with the previously reported ceramic systems. The <i>W</i>_D reaches 4.21 J/cm³ under 38 kV/mm at room temperature. Besides, a record high of power density (<i>P</i>_D ≈ 89.5 MW/cm³) in BNT-based ceramics is also achieved in <i>x</i> = 0.20 ceramic with an excellent temperature insensitivity within 25-160 °C. The <i>x</i> = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted <i>R</i>3<i>c</i> nanodomains and <i>P</i>4<i>bm</i> polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high <i>W</i>_D and <i>P</i>_D. Furthermore, the diffuse phase transition from <i>R</i>3<i>c</i> to <i>P</i>4<i>bm</i> phase on heating is considered to be responsible for the superior thermal stability of the high <i>W</i>_D and <i>P</i>_D. These results imply the large potential of the 0.80BNT-0.20NT ceramic in temperature-stable dielectric capacitor applications.