Crystal structure characteristics, intrinsic properties, and vibrational spectra of non-stoichiometric Ca1+ x WO4 ceramics

Non-stoichiometric Ca1+xWO4 ceramics were determined in a composition range of −0.04 ≤ x ≤ 0.04 by a conventional solid-state method. X-ray diffraction patterns show that the main phase is a tetragonal scheelite structure. Scanning electron microscopy images exhibited dense and uniform grains. The vibrational modes were assigned and illustrated in particular. A positive correlation exists between the full-width at half-maximum values of the Bg(Ca) Raman modes and the intrinsic losses simulated according to the damping factor and also a negative correlation between the Raman shifts of the ν4 (Bg) modes and the dielectric constants calculated by the Clausius-Mossotti (C-M) equation. The intrinsic properties of the samples were calculated by the four-parameter semi-quantum (FPSQ) model based on the far-infrared reflectivity spectra, which agreed well with those values obtained by the C-M and damping equations. At x = −0.01, the Ca0.99WO4 ceramic sintered at 1150 °C possesses the intrinsic properties of εr = 10.62 and tan δ = 4.62 × 10−4 based on C-M and damping equations and εr = 10.19 and tan δ = 2.35 × 10−4 deduced from the FPSQ model.