Microwave dielectric properties of the (1 − x)Mg2TiO4–xCaTiO3–y wt.% ZnNb2O6 ceramics system

Composite ceramics based on (1 − x)Mg2TiO4–xCaTiO3–y wt.% ZnNb2O6 (x = 0.12–0.16, y = 0–8) were prepared by a conventional mixed-oxide route. Zn2+ partially replaced Mg2+ in Mg2TiO4 and formed the spinel-structured (Mg1−δZnδ)2TiO4 phase. Nb2+, is known to be solid soluble in CaTiO3, was found to change its shape from cubic to pliable. A bi-phase system (Mg1−δZnδ)2TiO4 and CaTiO3 exhibited in all samples, where a small amount of second phase Mg1−δZnδTiO3 was also detected. The microwave dielectric properties of specimens were strongly related to ZnNb2O6 and CaTiO3 content. As y increased, ɛr and τf decreased, however, Q × f decreased to a minimum value and started to increase thereafter. It was also found that ɛr and τf increased and Q × f decreased with increasing x. The optimized microwave dielectric properties with ɛr = 18.37, Q × f = 31,027 GHz (at 6 GHz), and τf = 0.51 ppm/°C were achieved for (1 − x)Mg2TiO4–xCaTiO3–y wt.% ZnNb2O6 (x = 0.12, y = 4) sintered at 1360 °C for 6 h.