Barium Titanate Based High-Temperature Dielectric Materials Doped with Bismuth, Sodium, Lithium for Metamaterial Application

$\mathbf{(0.95-x)BaTiO_{3}-xNa_{0.5}Bi_{0.5}TiO_{3-0.05}Li_{0.5}Bi_{0.5}TiO_{3}}$ high-temperature capacitors were prepared by semi-oxalate method. The addition of $\mathbf{Li_{0.5}Bi_{0.5}TiO}_{3}$ does not affect the Curie temperature and decreases the sintering temperature from $\mathbf{1300^{\circ}{C} (in\ 0.9~BaTiO_{3}-0.1Na_{0.5}Bi_{0.5}TiO_{3})}$ to $\mathbf{1220^{\circ} {C}}$ (in $\mathbf{0.85{BaTiO}_{3}-0.1{Na}_{0.5}{Bi}_{0.5}{TiO}_{3}-0.05{Li}_{0.5}{Bi}_{0.5}{TiO}_{3})}$. With the increase in x value, Curie temperature in solid solutions increases. The grain size of sintered ceramics decreases with an increase in sodium and bismuth concentration due to the segregation of $\mathbf{Bi}^{3+}$ and $\mathbf{Na}^{+}$ ions at the grain boundary. The most attractive properties for application as high-temperature dielectrics are obtained in a material with $\mathbf{x}=0.1$ at less than 15% variation of relative permittivity of about 4200 between $\mathbf{20^{\circ}{C}}$ and $\mathbf{170^{\circ}{C}}$ at $\mathbf{1~kHz}$. Obtained $\mathbf{(0.95-{x}){BaTiO}_{3}-} \mathbf{xNa_{0.5}Bi_{0.5}TiO_{3}-0.05Li_{0.5}Bi_{0.5}TiO_{3}}$ solid solutions exhibited excellent temperature stable dielectric properties and are promising candidates for high-temperature multilayer ceramic capacitors for automotive applications.