An ultra‐low dielectric loss ceramics Mg2Ge0.98O4 with olivine structure was fabricated by conventional solid‐state route. The phase composition, crystal structure, and microwave dielectric properties were investigated. The phase of Mg2Ge0.98O4 is formed to the orthorhombic forsterite structure with a space group Pmnb (62). The dense microstructure and excellent microwave dielectric properties of Mg2Ge0.98O4 ceramic were obtained at 1360°C for 4 hours, with relative density ~96.4%, εr ~ 7.3, Q × f = 112 400 GHz, and τf ~ −64.6 ppm/°C. The conductive mechanism of Mg2Ge0.98O4 in the low frequency (<1 MHz) was studied by the dielectric spectroscopy and the result with Edc = 0.93 eV demonstrates that the defect was contributed to the double ionized oxygen vacancies. The intrinsic dielectric properties of Mg2Ge0.98O4 in the microwave region were obtained by infrared reflectivity spectra with εr ~ 7.13, Q × f = 120 400 GHz. And, acceptable τf (~+2.6 ppm/°C) of 0.92Mg2Ge0.98O4–0.08CaTiO3 composite ceramic was obtained by adding the CaTiO3.

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