High-Temperature Dielectrics in BNT-BT-Based Solid Solution

Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 (BNT-BT)-based ternary solid solutions were investigated for high-temperature capacitor applications. Through a comprehensive investigation of the (1 – $x$ )(0.92Bi 0.5 Na 0.5 TiO 3 -0.08BaTiO 3 )- $x$ NaNbO 3 [(1 – $x$ )(BNT-BT)- $x$ NN, $x= 0$ –0.45] system, 0.85(BNT-BT)-0.15NN was selected as the parent matrix due to its relatively high permittivity (>1800) and favorable energy-storage density (0.56 J/cm 3 at 7 kV/mm). The effect of bismuth substitution on the dielectric properties of the matrix was further characterized. The introduction of bismuth greatly broadened the operational temperature range of 0.85(BNT-BT)-0.15Na 1–3 y Bi y NbO 3 ceramics to over 327 °C for a ±15% tolerance. The dc resistivities were of the order of $10^{8}$ – $10^{11}~\Omega \cdot \text {m}$ magnitude from room temperature to 300 °C. An activation energy of 1.1–1.2 eV in 200–350 °C was obtained from dc resistivity data, suggesting that the conduction process in this temperature range may be associated with oxygen vacancy migration. Furthermore, the energy-storage properties were largely improved by the addition of bismuth. When the substitution of Bi over Na achieved was up to 7%, the energy-storage density and efficiency reached 0.62 J/cm 3 and 88% at 7 kV/mm, respectively. These results confirm that a BNT-BT-based solid solution is a promising candidate for lead-free high-temperature capacitor applications.