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## Detailed analysis of the charge transfer complex N,N-dimethylaniline-SO(2) by Raman spectroscopy and density functional theory calculations

ANDO, Romulo A.; MATAZO, Deborah R. C.; SANTOS, Paulo S.
Fonte: JOHN WILEY & SONS LTD Publicador: JOHN WILEY & SONS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Although the amine sulfur dioxide chemistry was well characterized in the past both experimentally and theoretically, no systematic Raman spectroscopic study describes the interaction between N,N-dimethylaniline (DMA) and sulfur dioxide (SO(2)). The formation of a deep red oil by the reaction of SO(2) with DMA is an evidence of the charge transfer (CT) nature of the DMA-SO(2) interaction. The DMA -SO(2) normal Raman spectrum shows the appearance of two intense bands at 1110 and 1151 cm(-1), which are enhanced when resonance is approached. These bands are assigned to nu(s)(SO(2)) and nu(phi-N) vibrational modes, respectively, confirming the interaction between SO(2) and the amine via the nitrogen atom. The dimethyl group steric effect favors the interaction of SO(2) with the ring pi electrons, which gives rise to a pi-pi* low-energy CT electronic transition, as confirmed by time-dependent density functional theory (TDDFT) calculations. In addition, the calculated Raman DMA-SO(2) spectrum at the B3LYP/6-311++g(3df,3pd) level shows good agreement with the experimental results (vibrational wavenumbers and relative intensities), allowing a complete assignment of the vibrational modes. A better understanding of the intermolecular interactions in this model system can be extremely useful in designing new materials to absorb...

## Raman spectroscopy of temperature induced effects in four carbon allotropes

Joya, M. R.; Zanatta, Antonio Ricardo; Barba-Ortega, J.
Fonte: World Scientific; Singapore Publicador: World Scientific; Singapore
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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In this paper, we report strong variations in the Raman spectra of different carbon allotropes samples, for temperatures ranging from 83 K to 1123 K. The temperature dependence of D and G peak frequencies in the Raman spectrum of diamond, graphite, graphene, and carbon nanoparticles (CNPs) with 20 nm dot-size were investigated. These effects caused by temperature can be estimated from the changes in position ( dω/dT )p and in linewidth of peak full width at half maximum (FWHM) G in the Raman spectrum of each sample. The broadening for each allotrope under the same conditions of temperature were: diamond ∼4 cm-1, graphite ∼50 cm-1, graphene ∼5 cm-1 and nanoparticles ∼7 cm-1. We also used scanning electron microscopy (SEM) to study the morphology and determine the size of the samples. According to the experimental data, the residual structural disorder and stress present in the samples are enhanced with temperature and responds for the observed changes in the Raman spectra. We present a systematic study of the temperature-dependent Raman spectra of four carbon allotropes.; CNPq; FAPESP; COLCIENCIAS (RC-N 696-2011); Dirección de Investigación Sede Bogotá (DIB) - Universidad Nacional de Colombia (UNAL)

## Espectroscopia Raman aplicada ao estudo de pigmentos em bens culturais: I - pinturas rupestres; Raman spectroscopy applied to the study of pigments in cultural goods: I - rupestrian paintings

Lopes, Francisco Nascimento
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Ziemath, Ervino C.; Aegerter, Michel A.
Tipo: Artigo de Revista Científica Formato: 216-225
ENG
Relevância na Pesquisa
486.06855%
Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.

## Espalhamento Raman por semicondutores mesoscópicos

Pedro Augusto Matos Rodrigues
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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Nós desenvolvemos um modelo para o espectro Raman de semicondutores microcristalinos. Neste modelo o confinamento dos fonons tem dois efeitos: a) produz uma relaxação da lei de conservação do momento cristalino; b) limita as vibrações óticas permitidas àquelas que satisfaçam a condição de onda estacionária. Estas modificações em relação a um cristal macroscópico resultam em um espectro Raman composto de vários picos que é claramente distinto daquele de um cristal macroscópico mesmo no caso em que o tamanho dos microcristais não é constante em toda a amostra. Nossos resultados são utilizados para caracterizar amostras de CdSe microcristalino obtido por deposição química; We developed a model for the Raman spectrum of small semiconductors crystallites. In this model phonon confinement has two effects: a) it produces a relaxation of the k conservation rule. b) it limits the amount of allowed optical vibrations to those which obey the stationary wave condition. These modifications with respect to macroscopic crystal result in a Raman spectrum containing several peaks which is clearly distinguished from that of bulk materials even in the case where the crystallite size is not constant throughout the sample. Our results are used to characterize microcrystalline samples of CdSe obtained by chemical deposition

## Transições de fase e efeitos anarmônicos nas vibrações da rede do LiI03 estudados com espalhamento Raman

Francisco Erivan de Abreu Melo
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
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O espectro Raman do LiIO3 foi estudado em função da temperatura (10K-680K) a pressão constante (1 bar) e em função de pressões uniaxial e hidrostática a diferentes temperaturas. No primeiro tipo de experiência, observamos duas mudanças descontinuas no espectro Raman com o aumento da temperatura. A primeira é reversível e ocorre num intervalo de temperatura entre 215ºC e 260ºC, dependendo da origem da amostra (pó ou monocristal) e de sua história térmica. A segunda ocorre para T ³ 290ºC e vem irreversível quando a amostra é aquecida acima de 340ºC. Cada fase tem um espectro característico e distinto dos outros dois. Embora a ocorrência destas transições de fases estejam em completo acordo com medidas de difração de raios-X e de análise térmica diferencial (DTA), elas estão em desacordo com trabalhos anteriores em Raman e infravermelho que não mostram mudanças qualitativas nos espectros na transição a Û g . Pensamos que este desacordo é devido que nossas medidas são as primeiras obtidas a temperaturas suficientemente altas para passarmos através das transições. Obtemos também destas experiências medidas quantitativas das dependências das freqüências dos fonons ativos no Raman e de suas larguras de linha com a temperatura na fase a. As medidas de pressão uniaxial foram realizadas nas temperaturas de 77K e 300K. As mudanças observadas nos espectros Raman foram bem descritas por uma teoria de potencial de deformação usada anteriormente para uma grande variedade de materiais. As medidas de pressão hidrostática foram realizadas nas temperaturas de 300K e 380K. A comparação destes resultados...

## Raman spectra and structural analysis in ZrOxNy thin films

Moura, C.; Carvalho, P.; Vaz, F.; Cunha, L.; Alves, E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Raman spectroscopy has been used as a local probe to characterize the structural evolution of magnetron-sputtered decorative zirconium oxynitride ZrOxNy films which result from an increase of reactive gas flow in the deposition The lines shapes, the frequency position and widths of the Raman bands show a systematic change as a function of the reactive gas flow (a mixture of both oxygen and nitrogen). The as-deposited zirconium nitride film presents a Raman spectrum with the typical broadened bands, due to the disorder induced by N vacancies. The recorded Raman spectrum of the zirconium oxide film is typical of the monoclinic phase of ZrO2, which is shown also by X-ray diffraction. Raman spectra of zirconium oxynitride thin films present changes, which are found to be closely related with the oxygen content in films and the subsequent structural changes.; European Union through the NMP3-CT-2003 505948 project "HARDECOAT"; FCT institution by the project nº POCTI/CTM/38086/2001 co-financed by European community fund FEDER

## Espectroscopia Raman aplicado ao beta-caroteno

PEREIRA FILHO, Daniel Palheta
POR
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## Low frequency Raman scattering in amorphous materials: fused quartz, "pyrex" boro-silicate glass and soda-lime silicate glass

Elozi, Khaled.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
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Raman scattering in the region 20 to 100 cm -1 for fused quartz, "pyrex" boro-silicate glass, and soft soda-lime silicate glass was investigated. The Raman spectra for the fused quartz and the pyrex glass were obtained at room temperature using the 488 nm exciting line of a Coherent Radiation argon-ion laser at powers up to 550 mW. For the soft soda-lime glass the 514.5 nm exciting line at powers up to 660 mW was used because of a weak fluorescence which masked the Stokes Raman spectrum. In addition it is demonstrated that the low-frequency Raman coupling constant can be described by a model proposed by Martin and Brenig (MB). By fitting the predicted spectra based on the model with a Gaussian, Poisson, and Lorentzian forms of the correlation function, the structural correlation radius (SCR) was determined for each glass. It was found that to achieve the best possible fit· from each of the three correlation functions a value of the SCR between 0.80 and 0.90 nm was required for both quartz and pyrex glass but for the soft soda-lime silicate glass the required value of the SCR. was between 0.50 and 0.60 nm .. Our results support the claim of Malinovsky and Sokolov (1986) that the MB model based on a Poisson correlation function provides a universal fit to the experimental VH (vertical and horizontal polarizations) spectrum for any glass regardless of its chemical composition. The only deficiency of the MB model is its failure to fit the experimental depolarization spectra.

## Raman Spectroscopy Study of Graphene Under High Pressure

Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
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Due to its exceptional mechanical and electrical properties, graphene (one layer sheet of carbon atoms) has attracted a lot of attention since its discovery in 2004. The purpose of this research is to compare the Raman spectra of graphene with plasma treated graphene sheets which have been treated by changing the different parameters affecting the plasma treatment like gas flow, power and pressure and treatment time. The graphene we used for our high pressure studies are 4-5 layer CVD deposited graphene samples prepared by our collaborators in Dr. W. B. Choi’s group. First we report a Raman spectroscopy study of graphene on copper substrate at high pressures. Diamond anvil cell (DAC) was used to generate pressure. In situ Raman spectra were collected at pressures up to 10 GPa. The results indicate that the G band of graphene shifts with pressure significantly (about 5 cm-1/GPa) whereas the 2D band changes very little. The plasma treated samples were loaded into DAC. Raman spectrum was captured. Parts of the spectrum which were not related to the grapheme peak position were eliminated. The background was reduced. Peaks were found and fitted using FITYK software and the shift of each peak compared to its last position was observed when the pressure was increased. Next we studied plasma treated graphene samples treated with different partial pressure treatments under high pressure and compared them to each other using zirconia anvil cell with the same method.

## Desenvolvimento de metodologias para o estudo do efeito Raman normal e ressonante utilizando modelos Ab initio dependentes do tempo; Development of methodologies for the study of normal and resonance Raman effect using Ab initio time-dependent models

Luciano Nassif Vidal
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Relevância na Pesquisa
480.65883%

## Normal coordinate analysis of the copper center of azurin and the assignment of its resonance Raman spectrum.

Thamann, T J; Frank, P; Willis, L J; Loehr, T M
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Normal coordinate analysis that utilizes a general valence force field and the Wilson FG matrix method has been applied to several structural models representing the active site of the blue copper protein, azurin. The models included tetrahedral and square planar CuN2SS', trigonal CuN2S, and trigonal bipyramidal CuN2SS'O structures in which the Ns are imidazole nitrogens of histidines, S is the thiolate sulfur of cysteine, S' is the thioether sulfur of methionine, and O is a peptide carbonyl oxygen. For constant Cu--ligand bond lengths and initial force constants, the force field was refined against the most intense of the observed frequencies (424, 404, 369, and 261 cm-1) in the resonance Raman spectrum of Pseudomonas aeruginosa azurin. The most satisfactory fit between observed and calculated frequencies occurs for tetrahedral and trigonal structures. The calculations provide detailed assignments for the resonance Raman spectrum of azurin and reveal considerable mixing of Cu--S(Cys) and Cu--N(His) vibrational modes. The trigonal model is favored because it is shown that the approximately equal to 260-cm-1 vibration is an invariant feature in the resonance Raman spectra of blue copper proteins, even those lacking a methionine in the vicinity of the copper atom. The present analysis ascribes the high frequencies of the Cu--ligand stretching modes and the resonance enhancement to the coupled nature of their vibrations and the Franck-Condon overlaps with predominant (Cys)S leads to Cu(II) charge transfer bands in the visible region.

## The Raman Spectrum of the Squarate (C4O4-2 ) Anion: An Ab Initio Basis Set Dependence Study

Miranda,Sandro G. de; Vazquez,Pedro A. M.
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
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The Raman excitation profile of the squarate anion, C4O4-2 , was calculated using ab initio methods at the Hartree-Fock using Linear Response Theory (LRT) for six excitation frequencies: 632.5, 514.5, 488.0, 457.9, 363.8 and 337.1 nm. Five basis set functions (6-31G*, 6-31+G*, cc-pVDZ, aug-cc-pVDZ and Sadlej's polarizability basis set) were investigated aiming to evaluate the performance of the 6-31G* set for numerical convergence and computational cost in relation to the larger basis sets. All basis sets reproduce the main spectroscopic features of the Raman spectrum of this anion for the excitation interval investigated. The 6-31G* basis set presented, on average, the same accuracy of numerical results as the larger sets but at a fraction of the computational cost showing that it is suitable for the theoretical investigation of the squarate dianion and its complexes and derivatives.

## Raman and surface enhanced Raman scattering of a black dyed silk

Garrido, C.; Espinoza Moraga, F.; Clavijo Campos, Rudecindo Ernesto; Gómez Jeria, Juan Sebastián; Araya Monasterio, C.; Icaza, M.; Campos Vallette, M. M.; Aguayo, T.
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo de revista
EN
Relevância na Pesquisa
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Artículo de publicación ISI; The Raman and surface enhanced Raman scattering (SERS) spectra of a black dyed silk sample (BDS) were registered. The spectral analysis was performed on the basis of Raman and SERS spectral data of isolated samples of Bombyx mori silk fibroin, its motif peptide component (GAGAGS) and the synthetic reactive black 5 dye (RB5). The macro FT-Raman spectrum of the silk sample is consistent with a silk II-Cp crystalline fraction of Bombyx mori silk fibroin; the SERS spectrum is highly consistent with conformational modifications of the fibroin due to the interactions with the Ag nanoparticles. The GAGAGS peptide sequence dominates the Raman spectrum of the silk. The SERS spectrum of the peptide suggests a random coil conformation imposed by the surface interaction; the serine residue in the new conformation is exposed to the surface. Quantum chemical calculations for a model of the GAGAGS–Ag surface predict a nearly extended conformation at the Ag surface. The Raman spectrum of the dye was analysed, and a complete band assignment was proposed; it was not possible to propose a preferential orientation or organization of the molecule on the metal surface. Quantum chemical calculations for a model of the dye interacting with a silver surface predict a rather coplanar orientation of the RB5 on the Ag metal surface. The Raman spectrum of the BDS sample is dominated by signals from the dye; the general spectral behaviour indicates that the dye mainly interacts with the silk through the sulphone (–SO2–) and sulphonate (–SO2–O–) groups. Besides the presence of dye signals...

## Raman spectrum and optical extinction of graphene buffer layers on the Si-face of 6H-SiC

Tiberj, A.; Huntzinger, J. R.; Camara, N.; Godignon, P.; Camassel, J.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The buffer layer has been analysed by combined micro-Raman and micro-transmission experiments. The epitaxial graphene growth on the (0001) Si face of 6H-SiC substrates was tuned to get a mixed surface at the early stage of graphitization with i) bare SiC, ii) buffer layer and iii) in some localized areas small monolayers flakes on top of the buffer layer. These unique samples enabled to measure the Raman spectrum of the buffer layer (close to the Raman spectrum of a carbon layer with a significant percentage of sp3 bonds) and its corresponding relative extinction at 514.5 nm. The Raman spectrum of the buffer layer remains visible after the growth of one monolayer on top but, despite the relatively low absorption coefficient of graphene, the Raman intensity is strongly reduced (typically divided by 3). The buffer layer background will bias usual evaluations of the domain sizes based on the D/G integrated intensities ratio. Finally, several Raman maps show the excellent thickness uniformity and crystalline quality of the graphene monolayers and that they are subjected to a non uniform compressive strain with values comprised between -0.60% and -0.42%.; Comment: submitted to Physical Review B

## Raman spectrum and charge fluctuations in the copper-oxide superconductors

Niksic, H.; Tutis, E.; Barisic, S.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
481.03156%
The effect of the charge fluctuations on the electronic spectrum and the Raman spectrum of high temperature superconductors is examined within the slave boson approach. Instead of using the saddle point approximation for slave bosons, we confine ourselves to the non-crossing approximation (NCA) in summing the diagrams for the Green functions, thus obtaining the renormalized hole spectrum and its lifetime on equal footing. The electronic Raman spectrum is calculated, showing the characteristic featureless behaviour up to the frequency of the order of renormalized $\Delta_{pd}$ parameter. The dependence on the polarization of the incident and the scattered light agrees with experiments.; Comment: 4 pages plus 3 compressed & uuencoded eps figures, LATEX 2.09, published in Physica C 235-240 (1994) 2265-2266, proceedings from the M2S-HTSC IV conference

## The effect of large $U_d$ on the Raman spectrum in the copper-oxide superconductors

Niksic, H.; Tutis, E.; Barisic, S.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The effect of the charge fluctuations on the electronic and Raman spectrum of high temperature superconductors is examined, using the slave boson approach to the large Coulomb repulsion $U_d$ on the copper site. Instead of the saddle point approximation $\srv{b}\ne 0$ for the slave boson, characteristic for various $N\ide\infty$ approaches, we confine ourselves to the non-crossing approximation (NCA) diagrams for the Green functions. In this way the effects of charge fluctuations and of the constraint of no double occupancy on the copper site on the shape of the electronic spectrum are studied primarily, while the slave boson diagrams responsible for copper-copper spin correlations are intentionally not included. The novel feature of the charge fluctuation dynamics shows up in the slave boson spectrum as the plateau extending over the range of 1eV below $\omega=0$. This is further reflected in the electronic Raman spectrum that we calculate for various combinations of the polarization of the incoming and scattered light. The Raman spectrum shows the characteristic featureless behaviour up to frequencies of the order of 1eV while the polarization dependence is also in qualitative agreement with experiment.; Comment: 20 pages plus 9 compressed & uuencoded ps figures...

## Energy Scales in the Raman spectrum of electrons and hole doped cuprates within competing scenarios

Valenzuela, B.; Bascones, E.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
482.97902%
Recent experiments in underdoped hole-doped cuprates have shown the presence of two energy scales in the Raman spectrum in the superconducting state. This feature has a natural explanation in some models in which pseudogap and superconductivity compete. In electron-doped cuprates antiferromagnetic correlations are believed to survive in the superconducting state, and to produce a pseudogap above the critical temperature. Contrary to hole-doped systems, in electron-doped compounds only one energy scale appear since the pair breaking Raman intensity peaks in both B$_{1g}$ (antinodal) and B$_{2g}$ (nodal) channels at a frequency of a few meV, typical of the superconducting order parameter. In this paper we analyze the different effect in the Raman spectrum of the competition between pseudogap and superconductivity in electron and hole-doped cuprates. The difference in energy scales in both systems is explained in terms of the different truncation of the Fermi surface induced by the pseudogap. For electron-doped cuprates we also analyze the spectrum with antiferromagnetism and a non-monotonic superconducting order parameter.; Comment: 7 pages, 4 postscript figures, minor changes in the text, Fig. 3 and Fig. 4 replaced to better visualize them

## Theory of the Raman spectrum of rotated double-layer graphene

Coh, Sinisa; Tan, Liang Z.; Louie, Steven G.; Cohen, Marvin L.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
487.92492%
We study theoretically the Raman spectrum of the rotated double-layer graphene, consisting of two graphene layers rotated with respect to each other by an arbitrary angle \theta. We find a relatively simple dependence of the Raman G peak intensity on the angle \theta. On the other hand, the Raman 2D peak position, intensity, and width show a much more complicated dependence on the angle \theta. We account for all of these effects, including dependence on the incoming photon energy, in good agreement with the experimental data. We find that it is sufficient to include the interaction between the graphene layers on the electronic degrees of freedom (resulting in the occurrence of van Hove singularities in the density of states). We assume that the phonon degrees of freedom are unaffected by the interaction between the layers. Furthermore, we decompose the Raman 2D peak into two components having very different linewidths; these widths are almost independent of the angle \theta. The change in the intensity and the peak position of one of these two components gives insight into the dependence of the overall Raman 2D peak features as a function of the angle \theta. Additionally, we show regions in the phonon spectrum giving rise to the Raman 2D peak signal. This work provides an insight into the interplay between the mechanical degree of freedom (angle \theta) and the electronic degrees of freedom (singularities in the density of states) in rotated double-layer graphene. Additionally...

## Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O·1CaO·3SiO2

Ziemath, Ervino C.; Aegerter, Michel A.
Fonte: Materials Research Society Publicador: Materials Research Society
Tipo: Artigo de Revista Científica Formato: 216-225
ENG
Relevância na Pesquisa
486.06855%
Precursor glass and glass-ceramics with molar composition 2Na2O·1CaO·3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm-1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm-1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm-1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.