Influence of ionic substitution on the microwave dielectric properties of Li₂Mg_0.95A_0.05TiO₄ (A=Ni, Co, Mn, Zn) ceramics

The rock-salt structured Li₂Mg_0.95A_0.05TiO₄ (A=Ni, Co, Mn, Zn) ceramics were prepared by the conventional solid-state method. The effects of different bivalent ions on the phase compositions, microstructure and microwave dielectric properties were investigated systematically. All the sintered samples exhibited a single phase with the space group of Fm-3m. The dielectric constants of Li₂Mg_0.95A_0.05TiO₄ ceramics were affected by the apparent densities and the dielectric polarizabilities. The Q·f values of Li₂Mg_0.95Co_0.05TiO₄ and Li₂Mg_0.95Zn_0.05TiO₄ ceramics were improved to ~110,000 GHz when the samples were sintered at 1350 °C. In addition, the temperature coefficient of resonant frequency showed no significant changes with the ionic substitutions. Typically, the Li₂Mg_0.95Co_0.05TiO₄ ceramics exhibited excellent microwave dielectric properties of ε _r=15.74, Q·f = 111,700 GHz and τ _f = −4.78 ppm/°C at 1350 °C. The Li₂Mg_0.95Zn_0.05TiO₄ specimens sintered at the same temperature also possessed similar dielectric properties with ε _r = 16.07, Q·f = 111,300 GHz and τ _f = −8.02 ppm/°C.