Lattice structure and microwave dielectric properties of [Mg0.5Si0.5]3+-doped LiAlO2 solid solution

Microwave dielectric properties of low-permittivity LiAl 1− x (Mg 0.5 Si 0.5 ) x O 2 (LAMS) ( x = 0.02–0.2) ceramics synthesised through solid-state reaction route were investigated. All compositions show pure LiAlO 2 phase with a P4 1 2 1 2 space group at x ≤ 0.18. Microstructure and relative permittivity ( ε r ) were greatly affected by the partial substitution of [Mg 0.5 Si 0.5 ] 3+ for Al 3+ site. Bond energy decreased with increasing x value, thereby increasing the temperature coefficient of resonant frequency ( τ f ) in the negative direction. Finally, the optimum microwave dielectric properties of LAMS ( x = 0.02) sample were obtained at 1300 °C with ε r = 6.17, Q × f = 53,300 GHz and τ f = − 129 ppm/°C. Then CaTiO 3 was added to the LAMS ( x = 0.02) material to adjust the τ f value to near zero.