Microwave dielectric properties of (1 − x)CaO-xBaO-Li2O-(1 − y) Sm2O3-yNd2O3-TiO2 ceramics system

The CaO-Li2O-Sm2O3-TiO2 system has been reported having a high dielectric constant and good temperature stability. Based on the composition of CaO : Li2O : Sm2O3 : TiO2 : = 16 : 9 : 12 : 63, the modifications of CaO and Sm2O3 were investigated. In this paper, CaO has been partially substituted by BaO and Sm2O3 by Nd2O3. It was found that the introduction of BaO leads the modified ceramics to be mixtures of two phases. The fQ value has been significantly promoted, while the dielectric constant can remain higher than 90. To obtain a higher dielectric constant, Sm2O3 has been further partially replaced by Nd2O3. The sintering temperatures for the property change were also studied. The temperature coefficient of resonant frequency could be varied from a positive value to a negative value according to the different sintering temperatures. Excellent dielectric properties of er = 103, fQ = 7200 and τf = + 2 ppm/°C were obtained with a composition of CaO : BaO : Li2O : Sm2O3 : Nd2O3 : TiO2 = 14 : 4 : 8 : 10 : 2 : 63 (molar ratio) and sintered at 1350°C for 3 h.