Infrared and raman investigations of the charge ordering phenomena in the monoclinic salts κ-(BEDT-TTF)4[M(CN)6][N(C2H5)4]·2H2O (M=CoIII, FeIII)

The monoclinic crystals of κ-phase charge-transfer salts formed by BEDT-TTF with Co(CN)₆ or Fe(CN)₆ anions undergo a phase transition at T=150 K. Temperature dependences of FT-NIR Raman spectra and IR reflectance spectra were studied. We show that the phase transition is related to a charge ordering and there exist charge fluctuations above 150 K.     

Infrared and Raman Investigations of the Charge Ordering Phenomena in the Monoclinic Salts κ-(BEDT-TTF)4[M(CN)6][N(C2H5)4]·2H2O (M = CoIII, FeIII)

The monoclinic crystals of κ-phase charge-transfer salts formed by BEDT-TTF with Co(CN)₆ or Fe(CN)₆ anions undergo a phase transition at T = 150 K. Temperature dependences of FT-NIR Raman spectra and IR reflectance spectra were studied. We show that the phase transition is related to a charge ordering and there exist charge fluctuations above 150 K.     

Growth and lattice dynamics of single-crystalline SnO2 nanowires prepared by annealing a gel precursor

A large amount of ultra-long single-crystalline SnO₂ nanowires were successfully synthesized through a polymeric sol–gel approach followed by a post-annealing in a crucible covered with a lid. The experimental results indicate that the product is composed of tetragonal SnO₂ nanowires, and moreover, their growth mechanism should arise from the self-catalyzed Sn-terminated polar surfaces due to the enrichment of Sn at the growth front of nanowires. In Raman scattering spectrum, in addition to three fundamental vibrational modes, some infrared (IR) active and surface phonon modes (SPM) are also observed due to size and shape confinement effects and surface disorder. Similarly, low frequency non-active IR and surface phonon mode absorptions are also observed in IR spectra.     

Infrared and raman spectroscopic studies on short-range structure of vitreous GeS2

The short-range struture of vitreous GeS₂ is investigated by infrared and Raman spectroscopy. The IR and Raman measurements were made on vitreous GeS₂ and also on a high temperature, α, and a low temperature, β, modifications of GeS₂ crystal. A striking similarity of the IR and Raman spectra features was found between vitreous GeS₂ and α-GeS₂, giving an evidence that vitreous GeS₂ is composed of tetrahedral GeS₄ units similar in structure to those in α-GeS₂. Furthermore the linkage of the GeS₄ tetrahedra may be presumed to be α-GeS₂-like in a short-range, namely two-dimensional.     

Composition of precipitates of barium and strontium nitrates crystallizing from nitric acid solutions

The chemical compositions of Ba(NO₃)₂ и Sr(NO₃)₂ precipitates obtained by precipitation from HNO₃ solutions of various concentrations were determined using an inert tracer. The data of chemical analysis and IR spectroscopy suggest the presence of HNO₃ in the precipitates of barium and strontium nitrates and of their solid solutions, formed from concentrated nitric acid solutions. The IR spectra of 0 to 23.5 M aqueous HNO₃ solutions were measured and compared to the spectra obtained by subtraction of the spectra of dry barium or strontium nitrate from the spectra of the wet crystals. The IR spectra and structure of the double salt K₂Ba(NO₃)₄ were also examined; they were found to differ from those of the components. The results of X-ray diffraction analysis are indicative of the formation of the precipitates with the structure similar to that of the dry salts, with simultaneously occurring changes in the texture of the precipitates formed from concentrated HNO₃. It was suggested that barium and strontium nitrates could form unstable adducts with HNO₃.     

Characterization of LiNbO3 nanocrystals prepared via a convenient hydrothermal route

LiNbO₃ nanocrystal was successfully prepared via a simple and convenient hydrothermal route using LiOH and Nb₂O₅ as the reactants. Transmission electron microscopy images shows that the as-prepared sample displays a flake-like shape of 40-100 nm. X-ray diffraction, IR spectrum and Raman spectra of the as-prepared sample indicates that the sample was well crystalline and of high purity.     

Molecular-dynamic modeling of the spectral characteristics of the ozone-water cluster system

The absorption of one to six ozone molecules by the (H₂O)₂₅ cluster is studied by the method of molecular dynamics under near-atmospheric conditions. The capture of O₃ molecules by a water cluster produces a decrease in the integral intensity of IR absorption, reflection, and Raman spectra. IR absorption spectra are highly sensitive to the number of ozone molecules absorbed by a water cluster. The observed photon emission time and the radiation intensity of a dispersed aqueous system with absorbed ozone molecules are appreciably reduced relative to the analogous characteristics of a pure water cluster system.     

Spectroscopic characterization of alkali borosilicate glasses containing iron ions

Structural properties of alkali borosilicate glasses containing iron ions were investigated using infrared, laser Raman and Mössbauer spectroscopy. Two types of glasses were prepared: SRL-type with the composition 18.5 wt% Na₂O, 10.0 wt% B₂O₃, 52.5 wt% SiO₂, 4.0 wt% Li₂O, 10 wt% TiO₂ and 5.0 wt% CaO, and sodium borosilicate glass with the composition 16.7 wt% Na₂O, 18.7 wt% B₂O₃ and 64.6 wt% SiO₂. Raman spectroscopy showed that orthosilicates are the dominant amorphous phase in the SRL-type of glass. Incorporation of iron in the SRL-type of glass induced polymerization of silicate units and -Si-O-Fe- copolymerization. It was concluded that different amorphous phases are simultaneously present in the SRL-type of glass containing iron ions. Interpretation of the Raman spectra is given. Incorporation of iron ions into the sodium borosilicate glass also affected the corresponding IR spectra. The valence state of iron and its coordination were determined by⁵⁷Fe Mössbauer spectroscopy.     

Influence of synthesis conditions on carbonate entrapment in perovskite SrSnO3

Strontium stannate (SrSnO₃), a perovskite material, was synthesized by the polymeric precursor method, with different routes to eliminate organic matter. The utilization of pure oxygen for the elimination of organic matter changed the Raman spectra, especially in the low frequency region. Some peaks, which were previously assigned to the perovskite phase, were not noticed when the carbonate amount was lower. On the other hand, the profile of the IR spectra and XRD patterns did not change. These results suggest that carbonate may be present inside the perovskite lattice.     

Infrared and Raman spectra and the band structure of yttrium trifluoride YF3

The infrared and nonresonant Raman spectra of YF₃ have been studied within the framework of density functional perturbation theory. We report the calculated frequencies of three Raman active modes and one IR active mode that could not be detected experimentally. The valence and conduction band structure of YF₃ have been calculated, using density functional theory. A good agreement between the calculated valence band width and experimental result was obtained, and an indirect energy gap of 7.58 eV is estimated in the local density approximation.     

Synthesis, crystal and molecular structure, and spectral properties of guanidinium salt of complex uranyl 2-methoxybenzoate

A crystalline uranyl 2-methoxybenzoate, [C(NH₂)₃][UO₂L₃]·H₂O, was synthesized. Its structure was determined by single crystal X-ray diffraction, and the electronic and IR spectra were recorded. The coordination number of the U atom is 8, with methoxyl O atom not involved in coordination bonding with uranyl. The structure contains a system of hydrogen bonds with water molecule of crystallization and guanidinium cation acting as proton donors. The electronic absorption spectrum of the crystalline complex has a pronounced vibronic structure, whereas in the solution spectrum all the lines are strongly broadened. This may be due to dissociation of the complex anion in solution, which leads to superposition of several spectra. In the IR spectrum, there is a set of band characteristic of guanidinium cations. The uranyl group in [C(NH₂)₃][UO₂L₃]·H₂O has almost symmetrical structure. Therefore, only the band of its antisymmetric vibrations is observed in the IR spectrum.     

Synthesis and study of new complex Pu(V) and Np(V) acetates

Double Pu(V) and Np(V) acetates of the compositions BaPuO₂Ac₃·2H₂O and SrAnO₂Ac₃·3H₂O with An = Pu and Np were synthesized in a well-crystallized form. In the dry state the compounds are stable in prolonged storage and are not hygroscopic. The plutonyl(V) and neptunyl(V) salts of the similar composition are isostructural. The IR spectra of the compounds were measured, and their behavior in heating was studied.     

Synthesis and study of Pu(V) formates

New double formates MPuO₂(OOCH)₂ (M = NH₄ and K) were isolated from neutral aqueous solutions. These compounds are isostructural to the Np(V) analogs. The unit cell parameters of the salts were determined by powder X-ray diffraction. The symmetry of the crystal lattice decreases from rhombic to monoclinic in going from the ammonium to the potassium salt. The electronic absorption spectra were recorded and analyzed. The thermal behavior of the Pu(V) compounds was studied. Their IR spectra were recorded. The hexagonal bipyramidal oxygen surrounding in the solid compounds was determined. Preparation of simple Pu(V) formates was attempted. The reasons preventing preparation of these compounds were analyzed.     

Structure of oxide gels and glasses by infrared and Raman scattering

Optically clear monolithic gels and fine gel powders have been synthesized using various alkoxide hydrolysis reactions. The gels have been characterized using various methods to determine their structures. (X-ray diffraction, DTA, TGA, DSC, IR and Raman spectroscopies). The spectra and the nature of gels depend on the solvent and the hydrolysis conditions (rate, pH, etc.). The use of acetone as solvent allows reduction of the hydrolysis time, from weeks to hours. If the hydrolysis of aluminium sec-butoxide is too rapid, at high pH, crystalline bayerite Al(OH)₃ is formed. Regular hydrolysis leads to amorphous optically clear gel with sometimes boehmite (or diaspore) traces. Formation of the (porous) glass (300 to 600°C) and also of the γ-alumina does not modify the Raman spectra strongly whereas large modifications are observed on IR spectra with the evolution of protonic species. The structure of alumina gel and glass is of the spinel type. The α-alumina phase grows above 1200 to 1250°C (above 1050°C if boehmite traces are present).     

Electronic Raman scattering as a probe of anisotropic electron pairing

A theory for the electronic contribution to Raman scattering in anisotropic superconductors is presented. It is shown that Raman scattering can provide a wealth of polarization-(symmetry-) dependent information which probes the detailed angular dependence of the energy gap. Using a model band structure, the symmetry-dependent Raman spectra are calculated for d_x2-_y2 pairing and compared to the data taken on Bi₂Sr₂CaCu₂O₈. Favorable agreement with the symmetry-dependent electronic spectra is shown. Further, the impurity dependence of theory is calculated, which provides an unique test of d_x2-_y2 pairing.     

Growth of Yb-doped YLiF4 laser crystal by the Czochralski method. Attempt of Yb energy level assignment and estimation of the laser potentiality

YLiF₄ (YLF) single crystals undoped and Yb³⁺-doped with different concentrations were grown by the Czochralski technique under CF₄ atmosphere. Detailed analysis of Yb³⁺-doped YLF spectroscopy were made to contribute to the determination of energy levels in this host. We are dealing with temperature and concentration dependences of both π and σ polarizations of the infrared (IR) absorption and emission spectra. Raman spectra were also used to give an attempt of interpretation of electronic and vibronic levels. The radiative energy transfer (self-trapping) and strong phonon–electron coupling make the assignment of Yb³⁺ energy levels difficult. Evaluation of the laser potentiality of this fluoride host is also presented.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

Preparation and structural studies in the (70 − x)TeO2–20WO3–10Li2O–xLn2O3 glasses

Quaternary tellurite glass systems (70 ? x)TeO₂–20WO₃–10Li₂O–xLn₂O₃ where x = 0, 1, 3 and 5 mol% and Ln are La, Pr, Nd, Sm, Er and Yb, respectively, have been prepared by the melt quenching technique. Densities of the obtained glasses were measured and the molar volume was calculated. IR absorption spectra of the present glass systems were determined at room temperature over the range of wavenumbers from 400–1,600 cm^?1. Raman spectra of the present glass samples were measured in the range of 30–1,030 cm^?1. Density, molar volume, IR and Raman spectra of the glasses were discussed by calculating average cross-link density, packing density, theoretically calculated Poisson’s ratio and number of bonds per unit volume of the studied glasses. Also, the quantitative interpretations were based on concentration of ions per unit volume of Te, Ln and O, short distance in nanometre between ions for (Te–O) of TeO₄ and TeO₃ groups, (W–O) of WO₄, WO₆ groups and calculated wavenumber, $ \bar{\upsilon } $ , for TeO₄ and TeO₃, respectively. The average stretching force constant that present in these quaternary glasses has been calculated in order to interpret the data obtained.     

Spontaneous Raman spectra of the crystalline, molten and vitreous rare-earth oxyorthosilicates

The polarized Raman spectra of Lu₂SiO₅ (LSO) and Gd₂SiO₅ (GSO) have been measured. The symmetries of the vibrational modes in the LSO and GSO Raman spectra were determined with using the group-theory calculations. Evaporation of SiO₂ from the LSO crystal at annealing above 2100 K and from the LSO melt was determined with High Temperature Raman Spectroscopy technique. It was found, that invert glasses with the LSO and GSO compositions could be synthesized by quick quenching their melts. The structure of these glasses was studied by means of the Raman spectroscopy data.     

Phonon spectra of eulytite crystals Bi4M3O12 (M = Ge,Si): ab initio study

In this paper we present the results of ab initio DFT calculation of phonon spectra for bismuth ortho-germanate Bi₄Ge₃O₁₂ and bismuth ortho-silicate Bi₄Si₃O₁₂ crystals, in the center of the first Brillouin zone. First, the geometry optimization was performed using the analytical energy gradients, with respect to atomic coordinates and unit cell parameters. Vibrational frequencies and normal modes were calculated within the harmonic approximation by diagonalizing the mass-weighted Hessian matrix. The IR and Raman spectra of both crystals were simulated with the periodic ab initio Crystal 09 code and B3LYP hybrid functional and the two sets of Transverse-Optical and Longitudinal-Optical frequencies are generated, together with their intensities. Also, the influence of isotopic substitution for Bi, Ge and O in phonon modes and the picture with values of frequencies shift in each mode by isotopic substitution were calculated. The obtained results are discussed and the comparision between the computed spectra and experimental data is quite satisfactory, which justifies the model and simulation scheme used for the title systems.