Ultra‐low Sintering Temperature Microwave Dielectric Ceramics Based on Na 2 O‐MoO 3 Binary System

The compounds in Na 2 O ‐ MoO 3 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 Na 2 MoO 4 , Na 2 Mo 2 O 7 and Na 6 Mo 11 O 36 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 Na 2 O ‐ MoO 3 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 Na 2 MoO 4 doesn't react with Ag and Al at 660°C. Also, Na 2 Mo 2 O 7 has a chemical compatibility with Al at 575°C.