Microwave dielectric properties and microstructural characteristics of aliovalently doped perovskite ceramics based on CaTiO3

XRD and microstructural analyses showed that CaTiO3 forms substitutional solid solutions with REAlO3 and REGaO3 (RE = La, Nd, Sm). With an increase in the concentration of REAlO3 and REGaO3 the temperature coefficient of resonant frequency (Tf) and the relative permittivity (epsilon (r)) decreased while the quality factor (Qxf) increased. The large positive tau (f) of CaTiO3 was completely compensated with an equimolar substitution of 30-35 mol % of Ca2+ and Ti4+. The 0.7CaTiO(3)-0.3SmAlO(3) solid solution exhibited a tau (f) congruent to 0 ppm/K, a epsilon (r) = 45 and a Qxf = 42.000 GHz. Partial substitution of Ca2+ with Mg2+, Ba2+ and Sr2+ reduced the Q value and increased the tau (f).