Low-Temperature Synthesis of CoNb2O6 Microwave Dielectric Ceramics

Low‐fired cobalt niobate (CoNb2O6) microwave dielectric ceramics were prepared through a developed sol–gel process using Nb2O5·nH2O as starting source. A metal‐dioxo‐bridged complex precursor was described on the basis of FT‐IR spectrum. The crystalline phases of calcined powders were characterized by X‐ray diffraction. Nanosized CoNb2O6 particles with orthorhombic α‐PbO2‐type structure were obtained above 750°C. There was no subsequent phase change upon sintering, and all compounds sintered to at least 94% of theoretical density. At 1000°C/4 h, CoNb2O6 ceramics exhibited εr ~ 21.9, Q × f ~ 66 140 GHz (at 8.9 GHz) and τf ~ −39.7 ppm/°C, having a good potential for low‐temperature cofired ceramic applications.