Superior Thermal Stability of High Energy Density and Power Density in Domain-Engineered Bi0.5Na0.5TiO3–NaTaO3 Relaxor Ferroelectrics

Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 – x)Bi0.5Na0.5TiO3–xNaTaO3 [(1 – x)BNT–xNT, x = 0–0.30] lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The x = 0.20 ceramic exhibits superior thermal stability of discharged energy density (WD) 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 WD reaches 4.21 J/cm3 under 38 kV/mm at room temperature. Besides, a record high of power density (PD ≈ 89.5 MW/cm3) in BNT-based ceramics is also achieved in x = 0.20 ceramic with an excellent temperature insensitivity within 25–160 °C. The x = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted R3c nanodomains and P4bm polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high WD and PD. Furthermore, the diffuse phase transition from R3c to P4bm phase on heating is considered to be responsible for the superior thermal stability of the high WD and PD. These results imply the large potential of the 0.80BNT–0.20NT ceramic in temperature-stable dielectric capacitor applications.