Crystal structure characteristics, intrinsic properties, and vibrational spectra of non-stoichiometric Ca1+xWO4 ceramics

Abstract

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.

Lattice vibrational characteristics and structures-properties relationships of non-stoichiometric Nd[Mg0.5Sn0.5(1+x)]O3 ceramics

“…As shown in Fig. 9d The dielectric contribution of the j th modes can be calculated applying the following equation 19…”

“…The crystal structures and phase components of the ceramics were characterized by X-ray diffraction (XRD) with the surface topographies being observed by scanning electron microscope (SEM). The Raman and far-infrared (FIR) spectra of NMS ceramics were construed at length based on the group theory and the space group information so as to obtain their lattice vibrational charicateristics 19 . The intrinsic properties were derived from the fitting of FIR peaks by a four-parameter semi-quantum (4-P) model, which were compared with the measured property values as well as the predicted values from Clausius-Mossotti equation (C-M) based on polarizability, respectively.…”

Crystal structure, dielectric properties, and lattice vibrational characteristics of LiNiPO4ceramics sintered at different temperatures

“…Therefore, the IR spectra of the LNP ceramics were fitted using Equations (12) and (13), and the patterns are shown in Figure 7. Eighteen IR modes were observed; the modes below 200 cm −1 are attributed to lattice vibrations, and those between 200 and 600 cm −1 are the vibrational modes of [LiO 6 ] and [ NiO 6 ].…”

“…In fact, understanding the lattice vibrational characteristics, including the assignment and illustration of phonon modes, by fitting and calculation of the lattice vibration peaks may clarify the inherent attributes and facilitate interpretation of the structure‐property relationship of microwave dielectric ceramics . Raman and far‐infrared (IR) spectroscopy techniques are widely used to analyze the optical phonons in materials and to explore the crystal structures of microwave dielectric ceramics . However, these techniques have not been applied together to analyze the lattice vibration characteristics of LiNiPO 4 (LNP) ceramics.…”

“…11 Raman and far-infrared (IR) spectroscopy techniques are widely used to analyze the optical phonons in materials and to explore the crystal structures of microwave dielectric ceramics. 12,13 However, these techniques have not been applied together to analyze the lattice vibration characteristics of LiNiPO 4 (LNP) ceramics. Therefore, we know little about the inherent attributes of lithium phosphate-based microwave dielectric ceramics with olivine structure, which hinders deep understanding and engineering applications of these ceramics.…”