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Composite ceramics based on the spinel Mg2TiO4 were prepared by a conventional mixed-oxide route. To achieve the temperature stabilization of the dielectric constant, each of the composites was added with 7 mol% CaTiO3. The effect of the substitution of isovalent Co for Mg on the microstructure and the microwave dielectric properties of the composite ceramics was also investigated. A maximum Q×f value of around 150–160 THz was obtained for the undoped Mg2TiO4, whereas a reduced Q×f value was observed for an increase in the Co concentration in the system (1−x)Mg2TiO4−xCo2TiO4. Upon doping with 7 mol% CaTiO3, the Q×f value passed through a maximum with increasing Co concentration. Adding ZnO–B2O3 to the composite system based on Co-doped Mg2TiO4 resulted in a reduction of the sintering temperature by 150°–200°C without any significant degradation in the Q×f value.

NaxCa1� xAl2� xSi21xO8 plagioclase solid solutions (0rxr1) were synthesized under sub-solidus conditions using a solid-state reaction technique. The plagioclase formation and the sintering temperature decreased with an increase in x from the anorthite (CaAl2Si2O8; x 5 0) to the albite (NaAlSi3O8; x 5 1). Microwave (MW) dielectric measurements revealed that