The (1−x)BaMoO4–xTiO2 (x = 0.0, 0.2, 0.3, 0.338, 0.4, 0.5, 0.66) ceramics were synthesized by the conventional mixed-oxide process. The sintering behaviors, phase composition, chemical compatibility with silver, and microwave dielectric properties of pure (1−x)BaMoO4–xTiO2 ceramics and 0.662BaMoO4–0.338TiO2 ceramic with H3BO3–CuO addition were studied. Infrared reflectivity spectra of (1−x)BaMoO4–xTiO2 (0.2 ≤ x ≤ 0.4) composites were measured in the range of 50–4500 cm−1 at room temperature. X-ray diffraction analysis reveals that scheelite BaMoO4 and rutile TiO2 phase coexist with each other at 1275°C and both of them do not react with silver (Ag) at 850°C. When the mole fraction of TiO2 (x value) is 0.4, a temperature stable microwave dielectric material is obtained, with εr = 13.8, Q × f = 40 500 GHz (f = 8.02 G), and τf = −6.13 ppm/°C. Complex dielectric spectra gained from the infrared spectra were extrapolated down to microwave range, and they were in good agreement with the measured microwave permittivity and dielectric losses. With 5 wt% H3BO3 and 1 wt% CuO addition, the 0.662BaMoO4–0.338TiO2 ceramics can be sintered well below 900°C, and possess good microwave dielectric properties with εr = 14, Q × f = 48 360 GHz, and τf = +13.9 ppm/°C.
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