Microwave dielectric properties of LaScO₃-TiO₂ materials

From fundamental ionic polarizability concepts, LaScO³ was projected as a candidate dielectric material for microwave application. The microwave dielectric properties of LaScO₃ were obtained as the dielectric permittivity of 24, Qxf of 18,000 GHz, with a temperature coefficient of resonant frequency (TCP) of -69 ppm/°C. Solid solutions and polyphase assemblages were investigated in the LaScO₃-TiO₂ system as a function of TiO₂ content, and correlated with the microwave dielectric properties. Orthorhombic perovskite LaScO₃ transformed to tetragonal symmetry with Ti substitution on the B-site of LaScO₃ owing to the ionic radius difference between Sc³⁺ and Ti ⁴⁺. With this phase transition, the formation of A-site vacancies (V_La‴) resulted in the precipitation of a La deficient secondary phase. The substitution of Ti also affected the dielectric properties. The dielectric constant increased and TCF became less negative with increased TiO₂ addition. However, the Qxf value decreased, due to the formation of the secondary phase. For the case of the 0.6LaScO₃-0.4TiO ₂ composition, a dielectric K of 40, Qxf of 6,000 GHz and nearly zero TCF were obtained.