A lattice dynamical investigation for the Raman and the infrared frequencies of Bi2W2O9

Studies on infrared and Raman-active phonons in the Aurivillius ferroelectric Bi₂W₂O₉ were performed theoretically. The Raman and infrared phonons were calculated by applying a short-range force constant model using normal coordinates having space group Pna2₁. Sixteen stretching, two repulsive and seventeen bending force constants were used for the calculations of the zone center phonons. The calculated Raman and infrared wavenumbers are in very good agreement with the experimental ones in the literature. Potential energy distribution for this compound has also been investigated for the contribution of each force constant towards the Raman and the infrared wavenumbers.     

Phonons at the zone center for α-NaAlH4

A short-range force constant model has been applied for the first time to investigate the phonons in α-NaAlH₄ having body centered tetragonal Scheelite structure .The normal symmetry coordinates for the Scheelite structure were computed to investigate the phonons at the zone center. The phonons for α-NaAlH₄ have been calculated involving five stretching and two bending force constants .The calculated Raman frequencies exhibit good agreement with the available measured values. The infrared frequencies have been assigned proper modes for the first time.     

Zone center frequencies of the orthorhombic NdMnO3 perovskite

A short range force constant model has been applied for the first time to investigate the phonons in NdMnO₃ perovskite in the orthorhombic phase. The calculations with nine stretching and eight bending force constants provide good agreement for the observed Raman frequencies. The infrared frequencies have been assigned for the first time.     

Lattice dynamical study of Sr2B′UO6 (B′=Ni, Co) double perovskites

A short range force constant model has been used within the normal coordinate analysis framework for the first time to investigate the lattice dynamics of Sr₂B′UO₆ (B′=Ni, Co) double perovskites having space group P2_1/n. The zone centre phonons have been calculated with ten stretching force constants and eight bending force constants in the nickel compound and ten stretching and nine bending force constants in cobalt compound. The theoretically obtained values of Raman and infrared wave numbers exhibit a satisfactory agreement with the experimental values. A complete assignment of these frequencies to specific modes has also been made.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis coupling constants,and e-species force constants of the molecules SPF3, FCCl3, and BrCCl3

The vapor phase Raman spectra of the molecules SPF₃, FCCl₃, and BrCCl₃ have been recorded at pressures of up to 1 atm over the fundamental frequency regions. The Raman band contours of the e-species fundamentals have been analyzed to yield first-order Coriolis coupling constants from which, together with the fundamental frequencies, e-species force constants of the general harmonic potential function have been evaluated. The results for thiophosphoryltrifluoride are compared with those deduced previously on the basis of infrared band contour analyses.     

The Raman and infrared spectra of vitreous BeF2

We report the polarized Raman spectra, the infrared reflectivity and the infrared dielectric constant of vitreous BeF₂, for vibrational frequencies up to 1500 cm^-1. The high frequency modes of the Raman spectrum are assigned to combination overtones as well as to transverse and longitudinal fundamental vibrations.     

High-pressure Raman and infrared study of ZrV 2O7

The room-temperature Raman and infrared spectra of zirconium vanadate (ZrV ₂O₇) were observed up to pressures of 12 GPa and 5.7 GPa, respectively. The frequencies of the optically active modes at ambient pressure were calculated using direct methods and compared with experimental values. Average mode Grüneisen parameters were calculated for the Raman and infrared active modes. Changes in the spectra under pressure indicate a phase transition at ∼1.6 GPa, which is consistent with the previously observed α (cubic) to β (pseudo-tetragonal) phase transition, and changes in the spectra at ∼4 GPa are consistent with an irreversible transformation to an amorphous structure.     

Raman and far-infrared spectra of NaCrS2

The Raman and far-infrared spectra of the layer structure compound NaCrS₂ have been investigated. Two Raman active modes have been identified and their observed symmetries are in accord with the R$\text{3}$m space group symmetry of NaCrS₂. Three of the four predicted infrared active modes have been observed. One of the infrared modes appears as a strong reststrahlen band indicating that the bonding in NaCrS₂ is partially ionic.     

Lattice dynamics of tetragonal R2BaCuO5 (R = La,Nd) oxides in the P4/mbm structure

A short‐range force constant model (SRFCM) has been applied to investigate the Raman and the infrared wavenumbers in R₂BaCuO₅ (R = La, Nd) in their tetragonal phase of space group P4/mbm. Calculations of zone‐center phonons are made with six stretching and five bending force constants. All the Raman and infrared values are then assigned to their corresponding modes. The force constants were evaluated by fitting ten Raman and eight infrared modes. The calculated Raman and infrared modes show good agreement with the observed values. Copyright © 2007 John Wiley & Sons, Ltd.     

Influence of crystal field potential on the spectroscopic parameters of SiO2·B2O3·PbO glass doped with Nd2O3

This paper presents the optical characteristics of Nd³⁺ silicate glass (SiO₂-B₂O₃-PbO), synthesized by the fusion method. Two sets of samples were prepared: glass and corresponding glass ceramics. Optical absorption, luminescence, Raman spectroscopy and atomic force microscopy (AFM) measurements were performed in order to determine the structural properties of the systems and the radiative characteristics of Nd³⁺ ions. Near infrared luminescence exhibited typical Nd³⁺ bands. Raman and AFM measurements indicated nanocrystal growth with thermal treatment of the glass ceramics. Judd-Ofelt calculations also confirmed that heat treatment induced structural rearrangement of the samples that was dependent on Nd₂O₃ concentration. This resulted in changes in the optical and physical properties of the samples, including stimulated emission cross section and rigidity.     

Optical phonons in CuAlS2

The optical phonons at k=0 of CuAlS₂ have been investigated by Raman scattering, infrared reflectivity and absorption measurements from 50 to 1000 cm^-1 at T=300 K. Eleven of the thirteen expected optically active phonons have been observed and identified with respect to their symmetry types. The phonon frequencies appear in a range from 498 to 76 cm^-1 with predominant polar modes at 445 and 266 cm^-1. The dielectric dispersion for E ⊥ c and E ∥ c has been determined by Kramers-Kronig integrations.     

Infrared and Raman spectra of MnS2

The infrared and Raman spectra of the pyrite-type crystal MnS₂ are reported. Nine of the ten optically allowed $\text{q≌0}$ phonons are observed. A comparison of the phonon frequencies with those of FeS₂ allows us to conclude that the electrostatic forces as well as the covalent sulfur-sulfur bonds are about the same strength in the two compounds. The short-range forces between metal and sulfur ions in the two cases, however, are quite different.     

The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

Effect of the internal rotation of the CHD2 group on the CH stretching infrared and Raman spectra of toluene C6D5CHD2 and nitromethane NO2CHD2 in vapor phase

Gas-phase infrared and Raman spectra of toluene C₆D₅CHD₂ and nitromethane NO₂CHD₂ were recorded in the CH stretching region. They are all characterized by a strong band with a weaker one at lower frequency. These bands have simple Raman profiles and their infrared contours are respectively of A and C type. A quantum theory of these spectra is put forward, assuming an anharmonic coupling of the νCH mode with the internal rotation of the CHD₂ group in the adiabatic approximation. Theoretical calculations based on this model give a good fit of the experimental Raman bandshapes and a good picture of the observed infrared spectra. Thus each of the observed bands can be characterized. The frequency of the intense band is the average of that of the νCH mode during the almost free internal rotation of the CHD₂ group, while the frequency of the weaker band is approximately equal to the minimal νCH frequency. This last one corresponds to the position of the CH bond in a plane perpendicular to that of the molecule (ν_⊥CH). The frequency difference between ν_∥CH (the CH bond being in the plane of the molecule) and ν_⊥CH is found to be 42 cm^?1 for the two compounds.     

Structural disorder and phase transitions in ZrO2-Y2O3 system

The phase transitions in the ZrO₂-YzO₃ system have been investigated as a function of temperature using Raman scattering. The cubic phase was found to be structurally disordered and the spectrum has been compared with a one phonon density of states derived from a rigid ion model. The frequencies and symmetries of the modes were obtained for the cubic, tetragonal and monoclinic phases and comparisons have been made between the various temperatures and compositions.     

Raman and infrared spectra of ZnSiAs2

The optical phonons at k = 0 of ZnSiAs₂ have been investigated by Raman scattering and infrared reflectivity measurements at 300 K. Eleven of thirteen expected optically active phonons have been observed and identified with respect to their symmetry types. The phonon frequencies appear in the range from 415 cm^-1 to 75 cm^-1 with predominant polar modes at 400 cm^-1 (gG₅), 389 cm^-1 (Γ₄) and 242 cm^-1 (Γ₄). The dielectric dispersion for E ⊥ c and E 6 c has been determined by Kramers-Kronig integrations.     

Raman spectra of TiO2-II,TiO2-III,SnO2, and GeO2 at high pressure

Raman spectra of the orthorhombic (II) and high pressure (III) phases of titanium dioxide at pressures to 372 kbar and effects of temperature and hydrostatic pressure on Raman spectra of the tetagonal cassiterite-like phases of TiO₂, GeO₂ and SnO₂ are described. At room temperature, the TiO₂ II–III transition is sluggish, and metastable coexistence was observed from 200 to 300 kbar. The Raman spectra of TiO₂-III imply that its primitive cell contains at least four formula units; however, the structure could not be established from the Raman spectra and available powder X-ray diffraction patterns.The temperature and pressure dependences of the spectrum of the tetragonal MO₂ phases together with bulk moduli and thermal expansion data were used to evaluate the pure-volume and pure-temperature contributions to the isobaric temperature dependence of the Raman frequencies. Large anharmonicities in TiO₂ are attributed to hybridization of the oxygen p states with the d states of the Ti ion. GeO₂, where p-electron bonding is involved, is much less Enharmonic.     

单壁BC3纳米管晶格动力学研究

基于力常数模型计算了一系列扶手椅型、锯齿型和手性单壁BC₃纳米管的声子色散关系.描述了单壁BC₃纳米管结构的表征方式,比较详细地给出了其结构、对称性和晶格动力学分析.基于数值计算结果,讨论了拉曼活性模和红外活性振动模的频率与管径的关系.由分析结果做出推断,BC₃纳米管的拉曼光谱和红外光谱比单壁碳纳米管更为复杂. 关键词： 3纳米管')" href="#">BC₃纳米管 声子色散关系 晶格动力学     

Vibrational properties of single-wall BC3 nanotubes

The phonon dispersions of single-wall BC₃ nanotubes with any chirality are calculated within a symmetry-based force constant model of the lattice dynamics. Based on the non-symmorphic symmetry group of the BC₃ tubes, the symmetries and number of the Raman- and infrared-active modes at Γ point of the one-dimensional Brillouin zone are given. The neighbor atom-atomic interaction force constants are recalculated by fitting them to the experimental phonon energy-dispersion curves of honeycomb BC₃ sheet. The frequencies of the optically active modes are presented as the function of diameters and chiralities for BC₃ tubes. The obtained phonon density-of-states spectra, phonon dispersion relations, and vibrational patterns of the zone-center phonons are presented and discussed in detail. The calculated frequencies of infrared-active modes are compared with the experimental values reported in the literature. The results provide comprehensive information about the vibrational properties of the BC₃ tubes and shed light on the interpretation of Raman scattering and infrared spectroscopies.