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–xLaVO4 (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 εr, quality factor Q × f, and resonant frequency τf 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 0.7LaNbO4–0.3LaVO4 ceramic sintered at 1160 °C possessed excellent microwave dielectric properties with an εr of ∼17.78, a Q × f of ∼75 940 GHz, and a τf of ca. −36.8 ppm/°C. This series of materials might be good candidate for microwave devices.