High-dielectric-constant and low-loss microwave dielectric in the (1 - X)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr _0.2)TiO₃ solid solution system

The microwave dielectric properties and microstructures of (1 - x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr _0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr _0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ε_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of -4.7 ppm/°C.