Phase evolution, phase transition, and microwave dielectric properties of scheelite structured xBi(Fe1/3Mo2/3)O4-(1-x)BiVO4 (0.0 ≤ x ≤ 1.0) low temperature firing ceramics

In the present work, the xBi(Fe1/3Mo2/3)O-4-(1-x)BiVO4 (0.0 <= x <= 1.0) ceramics were prepared via the solid state reaction method. All the ceramics can be densified at low sintering temperatures around 820 degrees C. At room temperature, the BiVO4 type scheelite monoclinic solid solution was formed in ceramic samples with a composition of x <= 0.10. When x lies between 0.1 and 0.7, a BiVO4 scheelite tetragonal phase is formed at room temperature. In the range 0.7 <= x < 0.9, the ceramic samples were found to be composites consisting of BiVO4 type tetragonal and Bi(Fe1/3Mo2/3)O-4 type monoclinic scheelite phases, and when x >= 0.9, the Bi(Fe1/3Mo2/3)O-4 type monoclinic scheelite solid solution was formed. In the BiVO4 type monoclinic solid solution region, the phase transition to tetragonal phase was studied by in situ Raman and Far-Infrared spectroscopies and by thermal expansion analysis. All of these methods indicated that the phase transition temperature almost linearly decreased from 255 degrees C for pure BiVO4 to about -9 degrees C for x = 0.1 sample. High performance microwave dielectric properties with a high permittivity of about 74.8, high Qf values above 11 500 GHz, and a small temperature coefficient of resonant frequency within +20 ppm per degrees C in a wide temperature range of 20-140 degrees C can be obtained in the composite ceramic sample with 60 mol% x = 0.10 composition and 40 mol% x = 0.02 composition. The xBi(Fe1/3Mo2/3)O-4-(1-x)BiVO4 (0.0 <= x <= 1.0) ceramics might provide useful candidate materials for microwave integrated capacitive devices, such as filters, antennas, etc.