Solid-state reaction mechanism and microwave dielectric properties of CaTiO3–LaAlO3 ceramics

• CaTiO3–LaAlO3 perovskite ceramics were prepared by four sintering reaction routes.
• The solid-state reaction mechanism was investigated by XRD and TG/DSC techniques.
• Sintering routes had more influence on the parameters of Q × f and τf than on εr.

0.675CaTiO3–0.325LaAlO3 perovskite ceramics were prepared by a conventional sintering process through four reaction routes. The solid-state reaction mechanisms were investigated by X-ray diffraction and thermogravimetric/differential scanning calorimetric analysis techniques. The results show that interactions occurred between mixtures of CaCO3 and TiO2 as well as La2O3 and Al2O3, and they can influence the sintering behavior of the mixtures. Prior to the formation of solid solutions, the perovskite phases CaTiO3 and LaAlO3 were formed regardless of the combination of oxide powders used as reagents. From the powder mixtures which were calcined at 1200 °C, a Ca-rich Ca9Al6O18 phase was present at 1400 °C if free La2O3 and Al2O3 used in the reaction mixtures. Ca-rich phases were also formed at higher temperature (1450 °C) if LaAlO3 was present. The densities of the ceramics obtained by the four routes were different at specific sintering temperatures, and the highest density was obtained for the reaction route two. Results indicated that the preparation pathways had more influence on Q × f and temperature coefficient of the resonant frequency (τf) than on the dielectric constants (εr), and Q × f decreased and τf increased rapidly when the secondary phase presented. Route four is considered as an optimal pathway for the preparation of 0.675CaTiO3–0.325LaAlO3 ceramics.

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