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Corundum structured Mg 4 Nb 2 O 9 dielectric ceramics with the excess of MgO were prepared by the sol-gel process and microwave dielectric properties were investigated with the excess of MgO. First, according to the stoichiometric ratio of Mg 4 Nb 2 O 9 phase formation was studied by means of XRD analysis by adjusting the ratio of Mg/Nb and the ratio was ranging from 0?5 to 2?4. Subsequently, based on phase formation microwave dielectric properties of Mg 4 Nb 2 O 9 ceramics as a function of ratio of Mg/Nb were obtained depending on phase change. The results showed that when the ratio of Mg/Nb was 2?1, pure phase of Mg 4 Nb 2 O 9 ceramics could be obtained at 1275uC with excellent microwave dielectric properties of e r 512?5, Qe5224,000 GHz, t e 5 242?8 ppm/uC.

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