Phase Evolution, Phase Transition, Raman Spectra, Infrared Spectra, and Microwave Dielectric Properties of Low Temperature Firing (K0.5xBi1-0.5x)(MoxV1-x)O4 Ceramics with Scheelite Related Structure

In the present work, the (K0.5xBi1-0.5x)(MoxV1-x)O-4 ceramics (0 <= x <= 1.00) were prepared via the solid state reaction method and sintered at temperatures below 830 degrees C. At room temperature, the BiVO4 scheelite monoclinic solid solution was formed in ceramic samples with x < 0.10. When x lies between 0.1-0.19, a BiVO4 scheelite tetragonal phase was formed. The phase transition from scheelite monoclinic to scheelite tetragonal phase is a continuous, second order ferroelastic transition. High temperature X-ray diffraction results showed that this phase transition can also be induced at high temperatures about 62 degrees C for x = 0.09 sample, and has a monoclinic phase at room temperature. Two scheelite tetragonal phases, one being a BiVO4 type and the other phase is a (K,B)(1/2)MoO4 type, coexist in the compositional range 0.19 < x < 0.82. A pure (K,Bi)(1/2)MoO4 tetragonal type solid solution can be obtained in the range 0.82 <= x <= 0.85. Between 0.88 <= x <= 1.0, a (K,Bi)(1/2)MoO4 monoclinic solid solution region was observed. Excellent microwave dielectric performance with a relative dielectric permittivity around 78 and Qf value above 7800 GHz were achieved in ceramic samples near the ferroelastic phase boundary (at x = 0.09 and 0.10).