Search

Phase pure LiCoPO4 (LCP) ceramic was prepared by a conventional solid-phase reaction, and the crystal structure and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD results showed that the LCP ceramic has an olivine structure (Pnma group) and the SEM images showed the clear grain boundaries and uniform grains in size. Raman scattering and far-infrared reflection spectroscopy were used to analyze the lattice vibrational characteristics of the phase pure LCP ceramic. The infrared spectrum was fitted based on the four-parameter semi-quantum model to obtain the intrinsic dielectric properties, which were consistent with the tested values as well as the theoretical values obtained from the Clausius–Mossotti and damping equation. Its performance parameters are comparable to DuPont's 9K7 products, and therefore, maybe a good candidate for 5G application. [ABSTRACT FROM AUTHOR]

The monoclinic β-Ga2O3 samples were prepared by the hydrothermal method. Production of phase pure β-Ga2O3 products with high crystallinity was demonstrated by X-ray diffraction analysis. Scanning electron microscope images revealed that the β-Ga2O3 microparticles are spindle shaped with layered sheet structures. Many nanopores are present on the surfaces of the β-Ga2O3 samples, which are formed by dehydroxylation of the GaOOH precursor by the two-phase transition that occurs during the calcining process. The Raman spectrum of β-Ga2O3 samples showed 11 active vibrational peaks, including the vibrational and translational modes of the GaO4–GaO6 chain, the regular octahedral GaO6-bending vibration mode, and the regular tetrahedral GaO4 stretching, as well as the bending vibration mode. Infrared spectroscopy showed a peak at 466.7 cm−1, corresponding to the Ga–O bond contraction vibration in the GaO6 regular octahedron, and a peak at 674.9 cm−1, corresponding to the shrinkage vibration of the Ga–O bond in the GaO4 regular tetrahedron. The ultraviolet emission peak at 398 nm in the photoluminescent spectrum is excited by the recombination of the donor formed by the oxygen vacancy and the acceptor formed by the gallium vacancy or gallium–oxygen vacancy pair. A weak ultraviolet emission peak is also observed at 275 nm. The growth mechanism of the β-Ga2O3 products was carefully analyzed and found to be mainly controlled by the Ostwald ripening mechanism. [ABSTRACT FROM AUTHOR]

A2MgWO6 (AMW, A = Ba, Sr, Ca) microwave dielectric ceramics were prepared by a traditional solid-phase synthesis method and then characterized by X-ray diffraction, scanning electron microscopy, Raman, and Fourier transform infrared spectroscopy. The XRD results showed that the main phase of the Ba(Mg1/2W1/2)O3 and Sr(Mg1/2W1/2)O3 samples was cubic perovskite (Fm-3m) and that of the Ca(Mg1/2W1/2)O3 sample was monoclinic perovskite (P21/c). The SEM images showed that the Sr(Mg1/2W1/2)O3 ceramic was composed of dense grains with a uniform particle distribution. It had a high degree of crystallinity, while the Ba(Mg1/2W1/2)O3 ceramic had many pores, and the Ca(Mg1/2W1/2)O3 ceramic had no obvious interfaces. The intrinsic properties were calculated by fitting the infrared spectra, which showed that the dielectric loss of the AMW ceramics was connected to the vibrations of the Mg/WO6 octahedra, and the dielectric constants were related to the central symmetric vibrations of A-site cations. The dielectric response mechanism of the AMW microwave dielectric ceramics was revealed by the lattice vibration, and the relationships between the crystal structure and dielectric properties were studied based on lattice vibrations. [ABSTRACT FROM AUTHOR]

LiMnPO4 (LMP) microwave dielectric ceramics were manufactured at different temperatures via a standard solid-state reaction method and the LMP ceramic sintered at 750 °C displayed dielectric properties of εr = 7.82 and Q × f = 29,189 (f = 12.7 GHz). The lattice vibrational characteristics of LMP ceramics were studied utilizing both infrared reflection and Raman scattering spectroscopy to clarify the basic principle of the dielectric response. The intrinsic properties that were fitted and simulated based on the infrared spectra agreed with the measured property values. The low-frequency vibrational modes contributed more to the dielectric properties than the high-frequency modes. Upon increasing the temperature, the permittivity was positively correlated with the bond length but showed the opposite trend of the Raman shift of mode 9 Ag(υ1). The Q × f value was positively correlated with the packing fraction but negatively correlated with the FWHM of mode 10 Ag(υ3). Thus, the structure–property relationships of LMP ceramics were established as a function of sintering temperature. [ABSTRACT FROM AUTHOR]

In this article, garnet-type Y3Al5O12 (YAG) were doped with Mg2+-Si4+ ionic pairs and its effect on the structure and the microwave dielectric properties was investigated. It was revealed that in ceramics Y3MgxAl5-2xSixO12 (x = 0, 0.5, 1.0, 1.5, 2.0), increasing doping concentration decreased the sintering temperature and time for the optimal densification. X-ray diffraction studies showed that the samples are isostructural to Al5Y3O12 garnet. All sample were formed a single phase except for x = 2.0, where a secondary peak was detected. Excellent microwave dielectric properties of εr = 10.56, Q × f = 67,571 GHz and τf = -35.23 ppm/°C were obtained for Y3Mg0.5Al4Si0.5O12 ceramics sintered at 1625 °C for 5 h. The factors influencing the microwave dielectric properties of Y3MgxAl5-2xSixO12 ceramics were further discussed by considering the ionic polarization, packing fraction, average grain size and chemical bond valence theory. [ABSTRACT FROM AUTHOR]

In this study, MgxY3-xAl5-xSixO12 (x = 0–0.6) ceramics were prepared via a high-temperature solid state method. Mg2+ and Si4+ replacing Y3+ ions at A-site and Al3+ at C-site in garnet-type Y3Al5O12 (YAG) ceramics were designed to discuss the effects of crystal structure, microstructure on microwave dielectric properties for the first time. Liquid phase sintering induced by doping of Mg2+-Si4+, significantly decreased the sintering temperature and time for the densification of YAG ceramics. X-ray diffraction of the samples showed single phase for x ≤ 0.5, while a secondary phase of MgAl2O4 formed for x = 0.6. From the Rietveld analysis, a decrease in lattice dimensions, bond length and valence and rattling effect were observed, while Raman results showed a change in FWHM of the Eg mode. Based on these parameters, a structure–property relation was developed for MgxY3-xAl5-xSixO12 ceramics. Specially, Mg0.1Y2.9Al4.9Si0.1O12 showed a good set of microwave dielectric properties sintered at 1575 °C for 4 h with εr = 10.67, Q × f = 58,799 GHz, τf = -29.5 ppm/°C. [ABSTRACT FROM AUTHOR]

A single phase BaTiO3 ceramic was prepared by traditional solid-state sintering process at 1220 °C for 4 h. XRD analysis results show that the obtained sample is tetragonal phase BaTiO3, the space group belongs to P4mm (No. 99). Lattice vibrational characteristics of BaTiO3 ceramic were revealed according to Raman and far-infrared spectroscopy. By fitting far infrared data with 4-P model, the dielectric constant (εr) of BaTiO3 ceramic is 20.0782, while its dielectric loss (tanδ) is 19.9756 × 10−4. The peak at 181 cm−1 has the greatest impact on the dielectric constant and dielectric loss. The theoretical dielectric properties of BaTiO3 ceramic were calculated by C–M and damping formulas, which εr = 20.1030 and tanδ = 19.1672 × 10−4. However, the theoretical data are too far different from the tested data, which is because the asymmetrical structure inside the tetragonal phase BaTiO3 generates spontaneously polarize along the C axis, forming a ferroelectric domain and resulting in an increase in the dielectric constants, and thus the dielectric loss also increases. [ABSTRACT FROM AUTHOR]

A phase pure Ba(Mg1/2Mo1/2)O3 (BMM) ceramic was prepared by a traditional solid-state reaction method with a double perovskite structure (Fm-3 m), which is confirmed by X-ray diffraction. The scanning electron microscope image of the BMM sample confirmed the presence of dense grains and clear grain boundaries. The Raman and far-infrared reflection spectra were measured, and the lattice vibrational modes were analyzed in detail. The intrinsic properties were fitted by the four-parameter semi-quantum model based on the far-infrared spectrum, whose values (εr = 4.728, tanδ = 4.594 × 10–4) were analogous to the theoretical values (εr = 4.290, tanδ = 5.962 × 10–4) calculated by the Clausius–Mossotti (C–M) and damping equations, as well as the measured values (εr = 4.468, tanδ = 4.439 × 10–4). [ABSTRACT FROM AUTHOR]

The non-stoichiometric Nd[Mg1/2(1+x)Sn1/2]O3 (NMS, − 0.04 ≤ x ≤ 0.04) were synthesized through a routine solid-state reaction process. The phase composition, phonon characteristics, and microwave dielectric properties were investigated by X-ray diffraction patterns, Scanning electron microscopy Raman and Fourier transform far-infrared reflection. The best crystallinity with uniformly distributed grains and clear grain boundaries at x = 0.01. The intrinsic properties were calculated by four-parameter semi-quantum model based on far-infrared reflectivity data, which agree well with those values obtained from the microscopic polarizabilities & damping coefficient angle. The correlations between intrinsic properties and lattice vibrational modes were discussed in particular. [ABSTRACT FROM AUTHOR]