Microwave dielectric properties of CaO-La2O3-Nb2O5-TiO2 ceramics

A series of ceramics with a general formula Ca1+xLa4-xNbxTi5-xO17 (0 a parts per thousand currency sign x a parts per thousand currency sign 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa4Ti5O17 and Ca5Nb4TiO17, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa4Ti5O17 and Ca5Nb4TiO17 coexisted and a trace amount of second phase was detected. The ceramics showed high epsilon (r) in the range of 45-52, relatively high quality factors with Q x f in the range of 9,870-15,680 GHz and tau (f) value in the range between -38 and -126.4 ppm/A degrees C. tau (f) of CaLa4Ti5O17 can be tuned to a near-zero value by addition of suitable amount of TiO2.