Microwave and infrared dielectric response of temperature stable (1-x) BaMoO ₄-x TiO ₂ composite ceramics

The (1-x)BaMoO ₄-xTiO ₂ (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)BaMoO ₄-xTiO ₂ ceramics and 0.662BaMoO ₄-0.338TiO ₂ ceramic with H ₃BO ₃-CuO addition were studied. Infrared reflectivity spectra of (1-x)BaMoO ₄-xTiO ₂ (0.2 ≤ x a;circ 0.4) composites were measured in the range of 50-4500 cm ^-1 at room temperature. X-ray diffraction analysis reveals that scheelite BaMoO ₄ and rutile TiO ₂ 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 TiO ₂ (x value) is 0.4, a temperature stable microwave dielectric material is obtained, with ε _r = 13.8, Q × f = 40 500 GHz (f = 8.02 G), and τ _f = -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% H ₃BO ₃ and 1 wt% CuO addition, the 0.662BaMoO ₄-0.338TiO ₂ ceramics can be sintered well below 900°C, and possess good microwave dielectric properties with ε _r = 14, Q × f = 48 360 GHz, and τ _f = +13.9 ppm/°C.