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.

No abstract

No abstract

A CaMgGeO₄ (CMG) ceramic with an olivine structure was fabricated by the traditional solid-phase reaction method; this material was dense at 1300 °C/6 h and exhibited excellent dielectric properties (ε_r = 6.83, Q × f = 125 432, f = 14.9 GHz).

BaWO4 ceramic is fabricated by conventional solid‐state reaction technique, and the intrinsic properties and the phonon characteristics of the ceramic are examined. The single‐phase BaWO4 is found in a tetragonal crystal structure as confirmed by X‐ray diffraction. Scanning electron microscopy shows well‐crystallized grains and uniform grain arrangement with clear boundaries. Raman vibrational modes are assigned, and the atomic motions of the modes are elucidated using first‐principles calculations. The intrinsic properties of the ceramic are evaluated by using the infrared vibrational mode results in a four‐parameter semiquantitative model, and the theoretical values obtained using the model are found to be in good agreement with the measured values. This analysis reveals the dielectric response mechanism of single‐phase BaWO4 ceramic. The contribution of each vibrational mode to the intrinsic properties is analyzed, and it is found that the Eu mode with a frequency of 102.02 cm−1 makes the most important contribution to the dielectric properties.