Microwave dielectric properties of low temperature firing Bi ₂Mo₂O₉ ceramic

Preparation, phase stability, sintering behavior, microwave dielectric properties of single-phase Bi₂Mo₂O₉ ceramic and its chemical compatibility with Ag have been investigated. The single-phase Bi₂Mo₂O₉ ceramic can be well densified in the temperature range from 620° to 645°C with relative density about 96%. X-ray diffraction data show that Bi₂Mo₂O₉ has a monoclinic structure (P2₁/n), with lattice parameters a=11.9664 Aå, b=10.8089 Aå, and c=11.8871 Aå. When sintering temperature ≥650°C, Bi₂Mo₃O₁₂ appears as a secondary phase. Pure monoclinic Bi₂Mo₂O₉ ceramic sintered at 620°C for 2 h exhibits good microwave dielectric properties with permittivity about 38, Q_f value about 12 500 GHz and temperature coefficient of resonant frequency about +31ppm/°C. The permittivity of single-phase Bi₂Mo₂O₉ corrected for porosity is about 40.17. However, the reaction between Bi ₂Mo₂O₉ and Ag will affect its further application in low-temperature cofired ceramic.