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)- xNN, 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
_1-3y
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
Ω · 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.