Preparation and characterization of CaTiO 3 –(Li 1/2 Nd 1/4 Sm 1/4 )TiO 3 microwave ceramics by a sol–gel combustion process

A novel sol–gel combustion process was adopted to synthesize reactive ceramic powder with composition of 0.25 CaTiO₃–0.75 (Li_1/2Nd_1/4Sm_1/4)TiO₃, and microwave dielectric ceramics were prepared at different sintering temperatures using the synthesized powder. The combustion behavior of citrate gel and the sintering feature of the synthesized powder were evaluated by using differential thermal analysis–thermogravimetric analysis and thermo-mechanical analysis techniques, respectively. The citrate gel exhibits a self-propagating behavior after being ignited in air at room temperature. The as-burnt powder is so highly reactive that it can be transformed into single-phase perovskite at 900 °C and it can be sintered at 1100 °C. The effects of sintering temperature on the density, microstructure, and dielectric properties of the sintered ceramics were investigated. The maximum values of density, dielectric constant, and Q×f were achieved after sintering at 1200 °C. At 1200 °C, very dense ceramics with uniform grains and good dielectric properties with a dielectric constant of 123.8, a Q×f value of 5110 (at 3.7 GHz), and a τ_f value of +12.5 ppm/°C were achieved via the sol–gel combustion route. PACS 77.84.Dy; 81.20.FW; 77.22.-d