A Chemical Route to BiNbO4 Ceramics

The liquid phase sintering of fine BiNbO4 powders allows to obtain dense ceramics with excellent microwave dielectric properties (ɛ=44–46; Q×f=16,500–21,600 GHz) at T≥700°C. The thermal decomposition of freeze‐dried precursors results in the crystallization of a metastable β′‐BiNbO4 polymorph that transforms into a stable orthorhombic α‐modification at T≥700°C. The dependence of sinterability on the powder synthesis temperature shows the maximum at 600°C, corresponding to the formation of crystalline BiNbO4 powders with a grain size 80–100 nm. Sintering temperature reduction to 700°C prevents the deterioration of silver contacts during co‐firing with BiNbO4 ceramics. In situ scanning electron microscopy observation of the morphological evolution during sintering shows that the intense shrinkage soon after the appearance of a CuO–V2O5 eutectics‐based liquid phase is accompanied by complete transformation of the ensemble of primary BiNbO4 particles.