Phase Evolution, Crystal Structure, and Microwave Dielectric Properties of Water-Insoluble (1-x)LaNbO4-xLaVO4 (0 ≤ x ≤ 0.9) Ceramics

In the present work, a series of low-temperature firing scheelite structured microwave dielectric in water-insoluble La2O3 Nb2O5- V2O5 system was prepared via the traditional solid-state reaction method. Backscattering electron diffraction, X-ray diffraction (XRD), energy dispersive analysis, and Rietveld refinements were performed to study the phase evolution and:crystal structure. In the full composition range of (1 - x)LaNbO4-xLaVO(4) (0 <= x <= 0.9) ceramics, at least four typical phase regions including monoclinic fergusonite, tetragonal sheelite, B -site ordered sheelite, and composite of monoclinic LaVO4 and tetragonal sheelite phases can be detected according to XRD analysis. The variations of, relative dielectric constant epsilon(r), quality factor Q x f, and resonant frequency tau(f) could be attributed: to Nb/V-O bond ionicity, lattice energy, and the coefficient of thermal expansion. Infrared reflectivity spectra analysis revealed that ion polarization contributed mainly to the permittivity in microwave frequencies ranges. Furthermore, the 0.7LaNbO(4)-0.3LaVO(4) ceramic sintered at 1160 degrees C possessed excellent microwave dielectric properties with an epsilon(r) of similar to 17.78, a Q X f of similar to 75 940 GHz, and a tau(f) of ca. -36.8 ppm/degrees C. This series of materials might be good candidate for microwave devices.