Ultra-low sintering temperature microwave dielectric ceramics based on Na₂O-MoO₃ binary system

The compounds in Na₂O-MoO₃ system were prepared by the solid-state reaction route. The phase composition, crystal structures, microstructures, and microwave dielectric properties of the compounds have been investigated. This series of compounds can be sintered well at ultra-low temperatures of 505°C-660°C. The sintered samples exhibit good microwave dielectric properties, with the relative permittivities (ε_r) of 4.1-12.9, the Q × f values of 19900-62400 GHz, and the τ_f values of -115 ppm/°C to -57 ppm/°C. Among the eight compounds in this binary system, three kinds of single-phase ceramics, namely Na₂MoO₄, Na₂Mo₂O₇ and Na₆Mo₁₁O₃₆ were formed. Furthermore, the relationship between the structure and the microwave dielectric properties in this system has been discussed. The average Na^I-O and Mo^VI-O bond valences have an influence on the sintering temperatures in Na₂O-MoO₃ system. The large valence deviations of Na and Mo lead to a large temperature coefficient of resonant frequency. The X-ray diffraction and backscattered electron image results show that Na₂MoO₄ doesn't react with Ag and Al at 660°C. Also, Na₂Mo₂O₇ has a chemical compatibility with Al at 575°C.