Temperature stable and high-Q microwave dielectric ceramics in the Li2Mg3-xCaxTiO6 system (x=0.00-0.18)

Microwave dielectric properties of Li2Mg3-xCaxTiO6 (x=0-0.18) ceramics were studied using a conventional solid-state route to find temperature stable and high Q microwave ceramics. As the calcination temperature was 500 degrees C, the Li2TiO3 phase with monoclinic rock salt structure in C2/c space group started to form. When the samples were calcined from 600 degrees C to 900 degrees C, the XRD patterns exhibited a remarkable chemical reaction between the MgO and Li2TiO3 phases, which eventually formed the Li2Mg3TiO6 phase. The results indicated the Li2Mg3TiO6 and CaTiO3 co-existed with each other and formed a stable composite system when the calcium content was added. The SEM photographs indicated that the pores caused by the Li evaporation could be effectively reduced due to the appearance of CaTiO3. As x was increased from 0 to 0.18, the relative density was significantly improved due to the elimination of pores. As the Ca content increased, the dielectric constant (er) increased from 14.8 to 20.6; the quality factor (Qxf) decreased from 148,713 GHz to 79,845 GHz, and the temperature coefficient of resonant frequency (If) significantly increased from 42.4 to +10.8 ppm/degrees C due to the increased amount of CaTiO3. Therefore, at x=0.12, the LMCxT ceramics sintered at 1280 degrees C for 6 h displayed excellent comprehensive properties of epsilon r=17.8,Qxf=102,246 GHz and iota f=-0.7 ppm/degrees C.