Additional Raman Bands Research Articles

Raman investigation of chalcopyrite oxidation

Raman spectroscopic investigations have been carried out on the oxidation, utilising ferric ion or potential control, of chalcopyrite in chloride and sulfate media. In chloride solutions the rate of oxidation was sufficient for the in situ examination of products, and elemental sulfur was found to develop heterogeneously on the mineral surface. The formation of an accompanying, Raman-inactive, phase was demonstrated from the appearance of additional Raman bands after irradiation of the oxidised surface with 442 nm light. The photo-induced product yielded a Raman spectrum consistent with polymeric sulfur and it is concluded that the parent compound is a metal-deficient sulfide having a remnant chalcopyrite lattice structure. This remnant phase was metastable at room temperature, decomposing relatively rapidly at temperatures >70 °C. Thiosulfate and other polythionate ions were not detected at the surface, nor were jarositic phases. There was little evidence for the formation of polysulfides. Chalcopyrite reacted slowly in sulfate solutions. Ex situ investigations in such media showed that similar products were observed as in chloride, although at a much slower rate and with less relaxation of the oxidised remnant lattice.

Improper hydrogen bonding and motional narrowing in binary mixtures of 2‐ and 3‐bromopyridine in methanol probed by polarized Raman study and DFT calculations

AbstractA concentration‐dependent Raman study of the ν(CBr) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH3OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm−1in the case of 2Br‐p and at ∼618 cm−1 in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(CBr) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.

Raman spectroscopy of halogen‐containing carbonates

AbstractRaman spectroscopy complemented with infrared spectroscopy has been used to study a series of selected natural halogenated carbonates from different origins, including bastnasite, parisite and northupite. The position of CO32− symmetric stretching vibration varies with the mineral composition. An additional band for northupite at 1107 cm−1 is observed. Raman spectra of bastnasite, parisite and northupite show single bands at 1433, 1420 and 1554 cm−1, respectively, assigned to the ν3 (CO3)2− asymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogenated carbonates is significant in that it shows distortion of the CaO6 octahedron. No ν2 Raman bending modes are observed for these minerals. The band is observed in the infrared spectra, and multiple ν2 modes at 844 and 867 cm−1 are observed for parisite. A single intense infrared band is found at 879 cm−1 for northupite. Raman bands are observed forthe carbonate ν4 in‐phase bending modes at 722 cm−1 for bastnasite, 736 and 684 cm−1 for parisite and 714 cm−1 for northupite. Multiple bands are observed in the OH stretching region for selected bastansites and parisites, indicating the presence of water and OH units in the mineral structure. The presence of such bands brings into question the actual formula of these halogenated carbonate minerals. Copyright © 2007 John Wiley & Sons, Ltd.

The luminescent carbon-bearing microinclusion enigma in the Kimi Unit, Rhodope, Greece: Raman microscopic point analyses and mapping with different lasers

The Kimi Unit of the Rhodope Metamorphic Province (RMP), NE Greece, experienced ultrahigh-pressure metamorphism (UHPM), as documented by the unequivocal presence of diamond microinclusions in metapelitic garnet porphyroblasts. Certain peculiar lozenge-shaped 2–8 μm sized inclusions in diamond-bearing garnets reveal a broad composite and asymmetric triplet band (phase XXX) at ∼1331 cm −1 in their Raman spectra acquired with a 632.8 nm He–Ne laser, initially attributed to an sp 3-hybridized C-polymorph. These have been meticulously re-investigated by means of combined 2-wavelength (514.5 nm/632.8 nm laser) Raman microscopy. Raman mapping has been extensively employed in order to examine the spatial distribution of phase XXX and of other phases in these polyphase inclusions and to explore for additional Raman bands. The triplet band at ∼1331 cm −1 measured with the 632.8 nm laser shifts to much higher wavenumbers (∼4966 cm −1) when excited with a 514.5 nm Ar + laser, proving that the XXX triplet is not a real Raman band but a luminescence one at ∼691.1 nm. Numerous hypotheses on the nature of the mysterious phase XXX (e.g. Cr 3+-bearing mineral, carbonate, C polymorph, gas, organic phase) are explored and discussed but all are shown to be unsatisfactory. It is suggested that XXX occurs as nanocrystals that luminesce strongly giving the appearance (in Raman maps) of being larger.

Nonlinear Shift of the Raman A1 Mode inGa-Incorporated CuInSe2 Thin Films

Composition dependence of quaternary CuIn1−xGaxSe2films on Ga content has been systematically investigated by Ramanscattering. The dominant A1 mode shifts from 174 cm−1 forCuInSe2 to 185 cm−1 for CuGaSe2 in an approximatelypolynomial curve other than a linear curve, indicating existence ofasymmetric distribution of Ga and In on a microscopic scale in films.With Ga content x>0.3, the significantly broadening andintensity decrease of A1 modes suggest the degradation ofcrystalline quality of chalcopyrite phase. Additionally, the quenchingof additional Raman band at 183 cm−1 for the Ga-rich filmsreveals that CuAu-ordered phase can coexist in nominal chalcopyriteCuInSe2 films but not in CuGaSe2, due to Ga inhibitioneffect.

Structural and physical properties of a novel TeO 2–BaO–SrO–Ta 2O 5 glass system for photonic device applications

A detailed study on a novel TeO 2–BaO–SrO–Ta 2O 5 glass system developed for photonic device applications is reported in this paper. The glass transition and crystallization temperatures could be selected by varying the Ta 2O 5 content in this glass system. This glass system is found to have good thermal stability among tellurite glasses. Raman spectroscopy has been used as a tool to analyze the structural details of this technologically important glass system. In addition to the TeO 4 trigonal bipyramid and TeO 3 trigonal pyramid structural units, glasses in this system revealed the presence of an additional Raman band attributed to TaO 6 octahedra. The Raman bandwidth of the present glasses are broader compared to the conventional tellurite glasses by 35%. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated. Unlike the other tellurite glasses, even at higher modifier concentrations the TeO 4 structural units dominate in the glass network compared to TeO 3 trigonal pyramids. The ratio of TeO 4/TeO 3 structural units was discussed for different series of glass compositions.

Raman spectroscopic study of mixed valence neodymium and cerium chloride solutions in eutectic LiCl–KCl melts

We have studied the Raman spectra of (NdCl2)–(NdCl3) and Ce–(CeCl3) mixtures in eutectic (LiCl)0.58(KCl)0.42 as solvent in the temperature range up to 600 °C. For the highly corrosive samples a windowless cell in connection with a Raman microscope was utilised. To our knowledge the Raman spectra of the solutions of NdCl2, CeCl3 and (most likely) CeCl2 in eut.–LiCl–KCl are shown here for the first time. In accordance with other rare earth halides described in the literature the Raman spectra of the pure trivalent systems are dominated by octahedral LnCl63− species which show a typical broad polarized band centred at 245 cm−1 for NdCl3 and 240 cm−1 for CeCl3, respectively. NdCl2 in (LiCl–KCl)eu shows a complex Raman spectrum consisting of depolarized bands. In mixtures of divalent and trivalent neodymium chlorides both spectra can be observed in parallel and no additional Raman bands appear. Solutions of cerium in CeCl3–(eut.–LiCl–KCl) show temporarily new Raman bands which are presumably due to divalent cerium chloride. These bands disappear in our samples after about 1 h since CeCl2 is not stable under the experimental conditions. Our findings are discussed in the light of the strongly different electronic transport properties in the neodymium and cerium systems.

Vibrational study and lattice dynamics of disordered NaBi(WO4)2

Polarized Raman and IR spectra were obtained for NaBi(WO4)2 crystal at ambient temperature. Assignment of the observed bands to the respective internal and external phonons was proposed on the basis of lattice dynamics calculations. The spectra showed also the appearance of additional Raman and IR bands which are not predicted from group theory for the scheelite I41/a structure. It is argued that these bands result from symmetry breakdown induced by cation disorder. Copyright © 2004 John Wiley & Sons, Ltd.

Chemical stability of SrCe 0.95Yb 0.05O 3− α in hydrogen atmosphere at elevated temperatures

The influence of water vapor pressure, P(H 2O), on chemical stability of SrCe 0.95Yb 0.05O 3− α under hydrogen atmosphere was investigated using XRD and Raman spectroscopy. From an XRD study, a second phase assigned to Sr 2CeO 4 was observed under strongly reducing conditions such as dry H 2 with P(H 2O)=4.6×10 Pa [ P(O 2)=3.1×10 −15 Pa] at 1273 K. From Raman spectroscopy, it was found that treated specimens under hydrogen atmosphere exhibited additional Raman bands, which may be assigned to the second phase. The relative intensity of the additional Raman band at 460 cm −1 drastically increased with decreasing P(H 2O) in the region P(H 2O)<7.0×10 2 Pa (2 °C sat.), whereas it was quite low in the region P(H 2O)>7.0×10 2 Pa [ P(O 2)>3.0×10 −14 Pa] at 1273 K. The perovskite phase proved to be stable against hydrogen with an increase in P(H 2O) or a decrease in temperature.

Infrared and Raman spectra of ZrSiO4 experimentally shocked at high pressures

AbstractZircon- and reidite-type ZrSiO4 produced by shock recovery experiments at different pressures have been studied using infrared (IR) and Raman spectroscopy. The v3 vibration of the SiO4 group in shocked natural zircon shows a spectral change similar to that seen in radiation-damaged zircon: a decrease in frequency and increase in linewidth. The observation could imply a possible similar defective crystal structure between the damaged and shocked zircon. The shock-pressure-induced structural phase transition from zircon (I41/amd) to reidite (I41/a) is proven by the occurrence of additional IR and Raman bands. Although the SiO4 groups in both zircon- and reidite-ZrSiO4 are isolated, the more condensed scheelite gives rise to Si–O stretching bands at lower frequencies, suggesting a weakening of the bond strength. Low-temperature IR data of the reidite-type ZrSiO4 show an insignificant effect of cooling on the phonon modes, suggesting that the structural response of reidite to cooling-induced compression is weak and its thermal expansion is very small.

Raman Scattering from Surface Phonons in Rectangular Cross-sectional w-ZnS Nanowires

Wurtzite (w-) ZnS nanowires with nearly square cross sections have been grown by pulsed laser vaporization of a (ZnS)0.9Au0.1 target in a flow of Ar 5%H2. Growth proceeds by the vapor−liquid−solid mechanism. Raman scattering from the ZnS nanowires in air at room temperature reveals a strong first-order longitudinal optic (LO) phonon (346 cm-1) and two transverse optic (TO) phonons (269 and 282 cm-1), as well as several second-order features. Peak assignments based on bulk ZnS can be made for all the first- and second-order features, except for one band located between the LO and TO bands. This additional Raman band is observed at 335 cm-1 in air, and downshifts to 328 cm-1 in dichloromethane (εm = 2.0) and to 326 cm-1 in aniline (εm = 2.56). This band is therefore assigned to surface optic (SO) phonons. The position of the SO band is consistent with a dielectric continuum model for rectangular cross section wires. A symmetry breaking mechanism which may activate the SO mode is also discussed.

In situ UV-vis-NIR diffuse reflectance and Raman spectroscopy and catalytic activity studies of propane oxidative dehydrogenation over supported CrO3/ZrO2 catalysts.

The molecular structures, oxidation states, and reactivity of 3 and 6% CrO3/ZrO2 catalysts prepared by incipient wetness impregnation were examined under different conditions. The in situ Raman spectroscopic studies under dehydrated conditions reveal that the 3 and 6% CrO3/ZrO2 catalysts possess equal amounts of monochromate and polychromate species. Consequently, monolayer coverage on this ZrO2 support is about 3% CrO3. The 6% CrO3/ZrO2 possesses an additional Raman band due to Cr2O3 crystals corresponding to the remaining 3% CrO3. Furthermore, during reaction conditions the polychromate species is preferentially reduced, the monochromate species are slightly affected, and the Cr2O3 crystals are not affected. The in situ UV-vis-NIR diffuse reflectance spectroscopy results reveal that under steady-state reaction conditions the extent of reduction and edge energy position of surface Cr6+ cations increase with an increase in reduction environment for the 3 and 6% CrO3/ZrO2 samples. Propane oxidative dehydrogenation (ODH) studies reveal that the catalytic activity expressed in moles of propane converted per gram catalyst per second is similar for the two catalysts, which is consistent with equal amounts of molecularly dispersed chromia present. The turnover frequency for the 6% CrO3/ZrO2 catalyst is, however, smaller than that for the 3% CrO3/ZrO2 sample due to the presence of Cr2O3 crystals, which are relatively inactive for propane ODH. For this catalytic system and for the experimental conditions used, propene, CO, and CO2 are primary products. Furthermore, the 33-39% propene selectivity is not affected by the C3H8/O2 ratio for both catalysts. Structure-reactivity studies suggest that the molecularly dispersed species are present in equal amounts in the 3 and 6% CrO3/ZrO2 samples as Cr6+ monochromate and polychromate species are the most effective catalytic active sites taking part in the propane ODH reaction.

Synthetic deuterated erythrite—a vibrational spectroscopic study

A comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm −1. The band at 3442 cm −1 is attributed to weakly hydrogen bonded water and the band at 3039 cm −1 to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm −1. The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm −1. Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm −1 and new bands are observed at 692, 648 and 617 cm −1. These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm −1 with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers.

Modification of Kaolinite Surfaces through Intercalation with Deuterated Dimethylsulfoxide

The surfaces of kaolinite have been modified through intercalation with deuterated dimethylsulfoxide (d-DMSO). X-ray diffraction shows the kaolinite to be expanded from 7.2 to 11.19 Å. Modification of the surface has been explored through (a) changes to the hydroxyl surfaces of the kaolinite and (b) through changes to the d-dimethylsulfoxide inserting molecule. Upon intercalation of the kaolinite with d-DMSO, additional infrared bands at 3660, 3538, and 3502 cm-1 and additional Raman bands at 3660, 3537, 3507, and 3480 cm-1 are observed. The first band at 3660 cm-1 is attributed to the inner-surface hydroxyls hydrogen bonded to the d-DMSO and the other bands to water hydroxyl-stretching modes. Both infrared and Raman spectroscopy shows that significant changes in the molecular structure of the d-DMSO occur upon intercalation. First, the CD stretching modes observed for d-DMSO at 2125 and 2249 cm-1 in the DRIFT spectrum lose the degeneracy and split into 2140 and 2127 cm-1 and 2267, 2250, and 2238 cm-1. The Raman spectrum shows this loss of degeneracy through the bands observed at 2272, 2267, 2263, and 2251 cm-1 for the antisymmetric CD stretching vibration and at 2129 and 2141 cm-1 for the symmetric stretching vibrations. Upon intercalation with d-DMSO, the SO stretching region shows bands at 1066, 1023, and 1010 cm-1. The 1066 cm-1 band is assigned to the free monomeric SO group and the 1023 and 1010 cm-1 bands to two different polymeric SO groups. Bands attributed to the CS stretching vibrations, the in-plane and out-of-plane SO bending and the CSC symmetric bends all move to higher frequencies upon intercalation with d-DMSO. It is proposed that intercalation depends on the presence of water and that the additional bands at 3536 and 3501 cm-1 are due to the presence of water. The precise positions of the hydroxyl stretching modes of water at these positions suggest that water is in a well-defined position within the intercalation structure.

Selenium dimers and linear chains in one-dimensional cancrinite nanochannels: Structure, dynamics, and optical properties

Cancrinite crystals possessing parallel nanochannels are attractive for incorporation of guest materials and preparation of one-dimensional structures. In this work, we study variety of cancrinite crystals synthesized with Se inside their channels. Single crystal x-ray diffraction, polarized Raman, optical absorption, and luminescence spectra are investigated. It is shown that Se is stabilized in the form of Se22− and Se2− dimers located in the center of the channel and oriented along the channel. Different absolute and relative concentrations of Se22− and Se2− are obtained for different samples. The Se22− dimers at high concentration show tendency to organize linear chains. At low temperatures, quite strong interdimer bonding for both Se22− and Se2− is observed. Another important low-temperature effect is appearance of additional Raman bands, which are attributed to the vibrations of linear Se22− chains distorted by the incommensurate potential of cancrinite. Strong near-infrared polarized luminescence is observed for all samples. Photoionization of dimers is shown to be important step in the mechanism of the luminescence.

Dependence of nanocrystalline SnO 2 particle size on synthesis route

Very fine SnO 2 powders were produced by (a) slow and (b) forced hydrolysis of aqueous SnCl 4 solutions and (c) hydrolysis of tin(IV)-isopropoxide dissolved in isopropanol (sol–gel route) and then characterized by X-ray powder diffraction, Fourier transform infrared and laser Raman spectroscopies, TEM and BET. The XRD patterns showed the presence of the cassiterite structure. As found from XRD line broadening the crystallite sizes of all powders were in the nanometric range. TEM results also showed that the sizes of SnO 2 particles in all powders are in nanometric range. Very fine SnO 2 powders showed different features in the FT-IR spectra, depending on the route of their synthesis. The reference Raman spectrum of SnO 2 showed four bands at 773, 630, 472 and 86 (shoulder) cm −1, as predicted by group theory. Very fine SnO 2 powders showed additional Raman bands, in dependence on their synthesis. The broad Raman band at 571 cm −1 was ascribed to amorphous tin(IV)-hydrous oxide. The additional Raman bands at 500, 435 and 327 cm −1 were recorded for nanosized SnO 2 particles produced by forced hydrolysis of SnCl 4 solutions. However, these additional Raman bands were not observed for nanosized SnO 2 particles produced by slow hydrolysis of SnCl 4 solution or the sol–gel route. The aggregation effects of nanosized particles were considered in the interpretation of the Raman band at 327 cm −1. The method of low frequency Raman scattering was applied for SnO 2 particle size determination. On the basis of these measurements it was concluded that the size of SnO 2 particles was also in the nanometric range and that, the sol–gel particles heated to 400 °C consisted of several SnO 2 crystallites.

Observation of sp3 bonding in tetrahedral amorphous carbon using visible Raman spectroscopy

Visible Raman spectroscopy excited at 532 nm was used to characterize the carbon bonding in tetrahedral amorphous carbon (ta-C) films. The vibrational modes of the sp3 bonding in ta-C films were revealed directly. An additional Raman band occurring below 1350 cm−1 was observed. It consisted of two features centered on ∼1270 and ∼1170 cm−1, which were associated with sp3 bond stretching. The observed sp3 related Raman spectrum approached the vibrational density of states of amorphous diamond.

Raman study on conformational equilibria of fluoroacetone in aqueous solutions

The effects of water and heavy water on conformational equilibria of fluoroacetone have been investigated via Raman spectroscopy. Additional Raman bands have been observed in the CF stretching and the CCC symmetric stretching regions for the aqueous solutions. Based on enthalpy and volume differences between the conformers, these bands are assigned to the syn conformer which has hydrogen bonds between the fluorine atom and water molecules ( syn′ conformer). The number of H 2O molecules binding to the syn′ conformer is estimated to be 2.4 from the concentration dependence of the spectrum. The enthalpy and the volume differences between the cis and syn conformers in the aqueous solutions show anomalous values in comparison with those in organic solvents. We discuss these thermodynamic behaviors from the viewpoint of the hydration structures of fluoroacetone.

Deintercalation of Hydrazine-Intercalated Low-Defect Kaolinite

AbstractThe deintercalation of a low-defect kaolinite intercalated with hydrazine was studied by X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), and Raman microscopy over 30 d. X-ray diffraction showed that the kaolinite was fully intercalated. More than 120 h were required for the hydrazine-intercalate to decompose. The Raman spectra of the hydrazine intercalate showed only a single band at 3620 cm−1, which was attributed to the innerhydroxyl group. Upon deintercalation, additional Raman bands were observed at 3626 and 3613 cm−1. These bands decreased in intensity with further deintercalation. As deintercalation proceeded, the bands assigned to the inner-surface hydroxyl groups at 3695, 3682, 3670, and 3650 cm−1 occurred and increased in intensity. DRIFT spectra showed two bands at 3620 and 3626 cm−1 for the fully intercalated kaolinite only. Upon deintercalation, an additional band assigned to intercalated water was observed at 3599 cm−1 and increased in intensity at the expense of the 3626-cm−1 band. Bands attributed to the innersurface hydroxyl groups increased in intensity with deintercalation. Both the Raman and DRIFT spectra showed complexity in the NH-stretching region with two sets of NH-symmetric and antisymmetric stretching bands. Deintercalation was followed by the loss of intensity of these bands. Significant changes were also observed in the hydroxyl deformation and water-bending modes as a result of deintercalation. A model of hydrazine intercalation of kaolinite based on the insertion of a hydrazine-water unit is proposed. The hydrated end of the hydrazine molecule hydrogen bonds with the innersurface hydroxyl groups resulting in the formation of a band at 3626 cm−1 in the DRIFT spectra.

New bulk and surface phonon–plasmon modes in Raman spectra of porous n-InP

We report the Raman study of porous doped InP. The additional Raman bands were found in comparison with unporous doped InP. The effective medium theory is used to show that these bands may be assigned to a new coupled LO-phonon–plasmon mode and a contribution from surface polaritons.