Papers by Keyword: Infrared Reflectivity

Abstract: 0.22CaTiO₃-0.78(Li_0.5Sm_0.5)TiO₃ + x wt% MgO (0.25 ≤ x ≤ 2.0) ceramics with pure perovskite structure were prepared by a conventional two-step solid-state reaction process. The effect of different content of MgO additive on the microwave dielectric properties of the 0.22CaTiO₃-0.78(Li_0.5Sm_0.5)TiO₃ ceramics was investigated in detail. The results of microwave dielectric properties showed that the permittivity (ε_r) and temperature coefficient of resonant frequency (τ_f) decreased gradually, while quality factor (Q×f) values increased when the x value increased. Raman spectra and infrared reflectivity spectra were used to study the relationship between vibrational modes and microwave dielectric properties. The harmonic oscillator model was used to fit infrared reflectivity spectra, and the obtained complex dielectric response was extrapolated down into the microwave region. It was found that the complex dielectric spectra were in good agreement with the measured microwave permittivity and dielectric loss. The 0.22CaTiO₃-0.78(Li_0.5Sm_0.5)TiO₃ + 0.50 wt% MgO ceramic sintered at 1240°C for 4 h exhibited good microwave dielectric properties with ε_r = 102.6, Q×f = 5084 GHz (at 3.8 GHz), and τ_f = -16.3 ppm/°C.

Abstract: Room temperature infrared transmittance and reflectance spectra of 4H and 6H-SiC single crystals were measured by a NEXUS 670 Fourier Transform Infrared-Raman spectrometer. The transmittance and reflectance of non-doped, V-doped semi-insulating (SI), high purity semi-insulating, n-type and p-type SiC wafers have been compared and assessed. The effect of nitrogen and boron concentration on the transmittance is discussed. In addition, the carrier concentrations in 4H-SiC wafers were measured by Raman spectroscopy at room temperature. The influence of nitrogen concentration on the transmittance is also discussed.

Abstract: We Report on the Structural and Vibrational Properties of the X = 0.11 and X = 0.33 Compositions of a New Class of Nanostructured Thermoelectric System (PbTe)1-X(PbSnS2)x by Means of X-Ray Diffraction, Scanning and Transmission Electron Microscopy and Infrared Reflectivity. both Compositions Are Phase Separated, where Pbsns2 Self-Segregates from Pbte to Form Features with Dimensions Ranging from Tens of Micrometers to Tens of Nanometers. Effective Medium Approximation Was Used in Order to Determine the Volume Fraction and the Dielectric Function of the Nanoscale Pbsns2 Embedded in Pbte. by Comparing the Phonon Parameters of the Nanoscale Pbsns2 and Bulk Pbsns2 Single Crystals, we Concluded that Phonon Confinement Effects and Bilayer Thickness Anisotropy within the Pbsns2 Nanostructures Embedded within Pbte Are Responsible for the Observed Variations in the Frequencies of the Shear and the Compression Modes Not Observed in Pure Crystals of Pbsns2.

Abstract: The reversible charge ordering transition of (Sm1-x,Cax)MnO3 is associated with strong changes in electrical, magnetic and infrared properties. In this work, normal spectral emissivity is calculated from infrared reflectance of bulk polished ceramics, measured by Fourier Transform Infrared Spectroscopy (FTIR). Emissivity versus temperature shows a sharp transition at the charge ordering transition. By comparing the apparent temperature of the sample with the absolute temperature, we show that (Sm1-x,Cax)MnO3 is a good candidate for infrared furtivity around room temperature.

Abstract: Nd0.3Sm0.7NiO3 ceramic has been synthesised using a sol-gel method and annealing at oxygen pressure. Nd0.3Sm0.7NiO3 exhibits a reversible metal insulator phase transition which is, in the infrared range, responsible of a thermal-optical contrast. Samples are structurally characterized by X-ray diffraction and thermogravimetric analysis. The Nd0.3Sm0.7NiO3 thermal – optical contrast is characterized in the mid-infrared range, using reflectance and thermal-optical measurements.

Abstract: The use of the optical spectroscopy techniques (Raman scattering, infrared reflectivity and photoluminescence) in characterization of nanopowders is presented. These techniques, as illustrated in the case of TiO2 and CeO2 nanopowders, offer the estimation of average grain size and size distribution, strain effects, porosity and nonstoichiometry.

Abstract: Infrared reflectivity measurements of GaN1-xPx alloys and quantitative fittings using Lorentz model have been carried out. In the GaN1-xPx alloys, two competitive mechanisms that determine the carrier concentration have been put forward. The one is from the effect of the isoelectronic traps which decrease the carrier concentration while the other is from the effect of defects which increase the carrier concentration. The calculated results of imaginary part of the elastivity of GaN and GaN1-xPx alloys show that the longitudinal optical phonon-plasmon (LPP) modes shift to high frequency direction and its linewidth gradually broadens with increasing carrier concentration in GaN1-xPx, indicating that the coupling of LPP modes gradually enhances and the damping of LPP modes gradually augments.