Lattice structure and microwave dielectric properties of [Mg_0.5Si_0.5]³⁺-doped LiAlO₂ solid solution

Microwave dielectric properties of low-permittivity LiAl_1−x(Mg_0.5Si_0.5)_xO₂ (LAMS) (x = 0.02–0.2) ceramics synthesised through solid-state reaction route were investigated. All compositions show pure LiAlO₂ phase with a P4₁2₁2 space group at x ≤ 0.18. Microstructure and relative permittivity (ε_r) were greatly affected by the partial substitution of [Mg_0.5Si_0.5]³⁺ for Al³⁺ 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 CaTiO₃ was added to the LAMS (x = 0.02) material to adjust the τ_f value to near zero.