Microwave dielectric properties and microstructure of Sm(Mg _0.5Ti_0.5-xSn_x)O₃ ceramics

Sm(Mg_0.5Ti_0.5-xSn_x)O₃ (x=0.1-0.5) ceramics were prepared by a conventional solid-state ceramic route. The microstructure and microwave dielectric properties were investigated as functions of Sn⁴⁺ substitution and the sintering temperature. A pure perovskite structure was obtained for samples with x=0.1-0.4, whereas small amount of second phase Sm₂Sn₂O₇ appears in the sample with x=0.5, which deteriorates the dielectric properties of the ceramics. Sn⁴⁺ substitution shows little influence on the sintering densification of the ceramics. With the increase of Sn⁴⁺ substitution, the dielectric constant and absolute value of τ_f for Sm(Mg_0.5Ti_0.5-xSn_x)O₃ ceramics decrease and increase, respectively. The Q×f of the ceramics can be improved by appropriate Sn⁴⁺ substitution. The Sm(Mg _0.5Ti_0.2Sn_0.3)O₃ ceramic sintered at 1625^oC for 3 h shows excellent microwave dielectric properties (ε_r=22.0, Q×f=72300 GHz, τ_f =-41.8 ppm/^°C), indicating that it could be used as a candidate compensate for the material with positive temperature coefficient of resonant frequency.