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.     

Size effect of trivalent oxides on low temperature phase stability of 2Y-TZP

2 mol% Y₂O₃stabilized-TZPs (2Y-TZPs) doped with oversized trivalent cations (Sc³⁺< Yb³⁺< Y³⁺< Sm³⁺< Nd³⁺< La³⁺) whose ionic radius is larger than Zr⁴⁺was sintered for 1 h at 1500°C over the range containing trivalent oxides from 0 to 2 mol% with 0.5 mol% interval to evaluate the effect of trivalent cation alloying on low temperature phase stability of 2Y-TZP by investigating the variation of Raman spectra and lattice parameters. For a given concentration of dopant, tetragonality (c/aaxial ratio) increases with raising the dopant size. However, monoclinic (m)-ZrO₂content for the specimens annealed for 500 h at 220°C in air firstly decreases with increasing dopant size and then increases as dopant size is greater than Y³⁺ion. Raman modes of Zr-O_II(260 cm^–1) and Zr-O_I(640 cm^–1) shift to higher wavenumbers only when Sm₂O₃, Nd₂O₃, and La₂O₃are added. Although full width at half maximum (FWHM) of 640 cm^–1is constant, FWHM of 260 cm^–1mode decreases with increasing dopant size, indicating that an ordered structure (pyrochlore phase) may be formed. Therefore, dopant size is dependent on phase stability of 2Y-TZP in this system.     

Infrared and Raman spectra of new molybdenum and tungsten oxyfluoride glasses

The infrared (400–1200 cm^–1) and Raman (200–1150 cm^–1) spectra are reported for the new AO₃-BaF₂-RF glasses where A is molybdenum or tungsten and RF is the alkali fluoride LiF, NaF and mixed LiF-NaF respectively. The observed absorption bands of each glass series were assigned to their vibrational modes. This study has shown that structural units formed in these glasses include [MoO₄] and [WO₄] tetrahedra, [MoO₆], [WO₆], [MoF₆] and [WF₆] octahedra groups.     

The vibrational spectra of MgO-Al2O3-SiO2 glasses containing TiO2

The infrared spectra from a series of MgO-Al₂O₃-SiO₂ glasses containing TiO₂ are consistent with the existence of a phase-separated structure consisting of a high silica phase and a high modifier phase of metasilicate composition. The invariance of the spectra throughout the range of pre-crystallization heat treatments and compositions precludes the possibility of significant changes in the average number of non-bridged oxygen ions per silica tetrahedron either during nucleation treatments or upon the addition of TiO₂ to the base glass. The Raman spectra from the same series of glasses consist of two main high-frequency bands, at 1000 and 910 cm^–1 which change markedly in relative intensity as TiO₂ is added to the base glass, and several subsidiary bands at lower frequencies. It is suggested that the high-frequency bands arise from two dissimilar metasilicate-type structures which are the pre-cursors of the major crystalline phases which precipitate upon devitrification of the glasses, namely cordierite in the low titania glasses (rings of [SiO₄]^2– tetrahedra), and a pyroxene similar to enstatite in the high titania glasses (chains of [SiO₄]^2– tetrahedra).     

Fast Li+ ion conduction in Li2O–(Al2O3 Ga22O3)–TiO2–P2O5 glass–ceramics

Fast lithium ionic conducting glass-ceramics have been obtained by heat-treatment of glasses in the systems Li₂O–M₂O₃–TiO₂–P₂O₅ (M = Al and Ga). The glass–ceramics were mainly composed of LiTi₂(PO₄)₃ in which Ti⁴⁺ ions were partially replaced by M³⁺ ions. Considerable enhancement of the conductivity with the substitution of M³⁺ ions for Ti⁴⁺ ions was observed. The maximum conductivity obtained at room temperature was 1.3 × 10^–3 S cm^–1 for the aluminium system and 9 × 10^–4 S cm^–1 for the gallium system.     

Crystallization kinetics and structure of (TeO2-TiO2-Fe2O3) Glasses

Crystallization kinetics and structure of (85TeO₂ + 15TiO₂) and (85TeO₂ + 10TiO₃ + 5Fe₂O₃) glasses are studied using differential scanning calorimetry DSC, IR spectroscopy and XRD. DSC curves in the temperature range from 50 to 525°C with different heating rates from 10 to 40°C/min are used to study the crystallization behavior of the glasses and effects of different heating rates on the glass transition and crystallization temperatures (T_g and T_p). The activation energies of the glass transition and crystallization processes were determined from the shift of T_g and T_p with the heating rates using Kissinger's formula. Effects of the polymorphic nature of TeO₂ on the crystallization mechanisms are discussed and the phases crystallized during the DSC process were identified by XRD. IR spectra in the frequency range (500–4000 cm^-1 ) are measured and possible coordination states of the constituent oxides are discussed for heat-treated and untreated glasses.     

Investigation of infrared absorption spectra of copper phosphate glasses containing some rare earth oxides

The spectra of copper-lutetium-phosphate and copper-erbium-phosphate glasses have been studied within the spectral range 4000 to 400 cm^– by Fourier transform infrared spectroscopy. Incorporation of a small amount of lutetium or erbium influences some band positions compared with binary copper phosphate glasses. The additional bands in the range 491 to 576 cm^–1 are attributed to the presence of Lu-O and Er-O groups. It has been observed that annealing of the samples at 500 ° C leads to a slight shift in the peak positions.     

Structural investigations of phosphate glasses: a detailed infrared study of the x(PbO)-(1−x) P2O5 vitreous system

The results and detailed discussion of an extensive experimental study of infrared spectra of the x (PbO)-(1–x)P₂O₅ vitreous system (x=0.3–0.75) together with a brief review of infrared spectra of phosphate compounds, are presented. Theoretical models employed in the interpretation of infrared spectra of glasses have been reviewed. The frequency ranges of various infrared bands belonging to PO ₄ ^3– and P₂O ₇ ^4– , observed in different phosphate compounds, are discussed. The glassy and quenched samples were prepared from PbO and NH₄H₂PO₄ by the rapid quenching technique. The infrared spectra of the constituents of the system, PbO and P₂O₅, in their polycrystalline and glassy forms, have been discussed. The intensity and wavenumbers of the infrared bands around 1600 and 3300 cm^–1, assigned to the bending and stretching modes in H₂O trapped by the hygroscopic glasses, have been followed for different compositions with x<0.5. The changes observed in these infrared bands established the role of water as an additional glass modifier. The intensity and frequency variations of the infrared bands have been followed through all the compositions for characteristic phosphate group frequencies including P=O, P-O-P stretching and bending modes and P-O bending mode. The results clearly suggest that the x(PbO)-(1–x)P₂O₅ system undergoes gradual structural changes from metaphosphate (x=0.5), to pyrophosphate (x=0.66) and to orthophosphate (x=0.75). The continuing presence of the infrared band, in varying intensity, in the region 1200–1280 cm^–1 attributed to P=O, suggests that the glass-forming ability of the binary system is extendable at least up to x=0.66 composition, and that no complete rupture of P=O bond by Pb²⁺ takes place. The ionic character of the phosphate groups, P-O^(–), PO ₄ ^3– is well revealed by significant changes with the PbO content in the spectral features of the infrared bands around 1120 and 980 cm^–1 respectively. The maximum intensity of the P-O^(–) band at 1120 cm^–1 for 55 mol% PbO suggests a partial breakdown of the covalent vitreous network of the phosphates and formation of a crystalline phase consisting of ionic groups PO ₄ ^3– , P₂O ₆ ^2– and P₂O ₇ ^4– for PbO greater than 55 mol%. The observed pattern of variation in the intensity of the infrared bands in the 940–1080 cm^–1 region attributed to the v₃-mode in PO ₄ ^3– , suggests a gradual transformation of PO ₄ ^3– units to PO ₃ ^– groups in lead meta-phosphate glass and then their restoration to PO ₄ ^3– groups of pyro- and ortho-phosphate quenched samples. The results indicate a gradual decrease in the number of bridging oxygens and increase in the resonance behaviour of non-bridging oxygens as the mole percentage of metal oxide (PbO) increases in the glass. The infrared spectra of several binary phosphate glasses have been reviewed in the context of the study of effect of the cation on the infrared spectra. It is found that the influence of the cation on the infrared spectra of phosphate glasses does not show any striking regularity. Theoretical calculations of these band frequencies were found to agree well only in the case of pure stretching (P=O and O-H) vibrations and pure bending (P-O-P and O-H) vibrations. The disagreement in the case of P-O^(–), P-O-H and other modes of P-O-P groups, has been attributed to the mixed nature of modes occurring in glasses. The changes in the positions of the characteristic bands and their relative intensities are strongly dependent on the structural units and PbO content in the phosphate glasses and the results emphasize the role of PbO as a network modifier.     

Raman spectroscopic investigation of sodium borosilicate glass structure

Raman spectra of sodium borosilicate glasses with a wide range of Na₂O/B₂O₃ ratios were systematically measured. Variations of the spectra with glass composition were studied to interpret the implied distribution of Na⁺ ions between silicate and borate units. When Na₂O/B₂O₃ is less than 1, all Na⁺ ions are associated with borate units as indicated by the absence of the 1100 cm⁻¹ band of Si-O⁻ non-bridging bond stretching. For the (1−x)Na₂O · SiO₂ ·xB₂O₃ glass withx≦0.4 the peak-height ratio of the 950 cm⁻¹ band to the 1080 cm⁻¹ band was used to analyse semiquantitatively the distribution of the Na⁺ ions between silicate and borate units. Sodium ions are divided between silicate and borate units approximately in proportion to the amount of SiO₂ and B₂O₃ present in these glasses. Some of the high sodium content glasses were crystallized and their spectra were compared with the bulk glass spectra. The distribution of Na⁺ ions in the glass was quite different from their distribution after crystallization. Spectra of high silica glasses that had been heat-treated for phase separation indicated exclusion of borate units from the silica network and the formation of borate groups. For high boron content glasses, no change was observed on heat treatment. Raman bands due to borate groups seem to be little affected by their environments. Also affiliated with the Department of Geosciences.     

Glass formation region and lithium ion conduction in the oxyfluorophosphate glasses

Oxyfluorophosphate glasses containing about 80 mol% of [LiF+Li₂O] show unusually high lithium ion conductivity at elevated temperatures. A detailed investigation has been carried out on the glasses prepared by both conventional cooling and a rapid quenching technique. Chemical analysis of the glasses reveals fluorine loss during melting and it becomes difficult to make glasses with exact predetermined compositions. Electrical conductivity of the glasses, determined from complex impedance analysis increases with Li₂O content. A glass with nominal composition 70 LiF15 Li₂O15 Al(PO₃)₃ shows the highest conductivity (~ 1.3×10^–3 ohm^–1 cm^–1 around 200° C) among all the compositions studied. An interesting feature of the impedance plot is the near perfect semicircle for bulk relaxation indicating a narrow distribution of relaxation times. This has been explained on the basis of a relatively small proportion of lithium ions which are mobile. The electrical conductivity of the glasses is found to be essentailly independent of dissolved water content. The infrared spectra of these glasses (2 to 50m region) could not produce much useful structural information.     

Structure of WO<Subscript>3</Subscript>-TeO<Subscript>2</Subscript> glasses

WO₃-TeO₂ glasses have been studied by quantum-chemical simulation and Raman spectroscopy. The results have been used to develop a model for the network of tungstate-tellurite glasses. The model allows one to correlate the structure and optical properties (in particular, the position and intensity of Raman bands) of the glasses with their composition. The network of the glasses is shown to be made up, for the most part, of three types of structural groups: TeO₄ trigonal dipyramids, O=TeO₂ pyramids, and O=WO₅ octahedra. Any other structural units, in particular, WO₄ tetrahedra, are unnecessary. The model for the network of WO₃-TeO₂ glasses can be used to analyze the vibrational spectra of tungstate-tellurite glasses in a broad composition range. In particular, using this model we assigned the Raman spectra of the tungstate-tellurite glasses in the range 550–950 cm^?1.     

Infra-red study of polymerisation in silver,thallium, and thallium aluminogermanate glasses

The infra-red spectra of silver germanate, thallium germanate, and thallium aluminogermanate glasses are presented for the 1100 cm^–1 to 400 cm^–1 region. The pseudo rare gas type Tl⁺ and Ag⁺ ions produce spectral shifts in binary germanate glasses that are similar to those reported for alkali ions. Differences for Tl⁺ may be due to its high atomic weight and polarising power. The infra-red spectral shifts observed for thallium aluminogermanate glasses are those expected if GeO₆ octahedra disappear while AlO₄ tetrahedra engage in network repair. A structurally sensitive technique for displaying ternary oxide glass infra-red spectra is outlined. This technique is capable of discerning different modes of network depolymerisation and polymerisation in ternary germanate and silicate glasses.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.     

Infrared spectra and composition dependence investigations of the vitreous V2O5/P2O5 system

A series of glasses in the V₂O₅-P₂O₅ system was prepared and their compositions analysed. The glass densities and molar volumes were determined. The results obtained revealed three compositional regions. In addition, the infrared absorption spectra of these glasses were measured at room temperature in the frequency range 1600–200 cm^–1. The compositional dependence of the bands present, attributed to a given band and mode of vibration, was investigated. However, the infrared data confirmed the results obtained from the density and molar volume measurements.     

The effects of various hydrothermal treatments on magnesium-aluminium hydrotalcites

Mg/Al hydrotalcites were synthesised by coprecipitation followed by hydrothermal treatment. The materials were characterised by XRD, infrared and Raman spectroscopy, electron microscopy and thermal analysis. The XRD pattern obtained was typical of a hydrotalcite, where the interlayer anion is CO₃ ^2–, with a basal distance of 23.5 Å. All possible CO₃ ^2– modes were observed in the infrared and Raman spectra, at 1068 cm^–1, 844 cm^–1, 1380 cm^–1, and 680 cm^–1. XRD, Infrared and Raman spectroscopy complimented each other by showing that with treatment the degree of order increased regardless of the type of treatment. Furthermore, it was shown that aging at increased temperature and pressure increased crystallinity and that treatment in water rather than in the mother liquid resulted in a more crystalline material. TEM showed that crystal size increased with aging, such that growth occurred on the edges resulting in the formation of hexagonal plate shaped hydrotalcite crystals. Thermal analysis showed 3 major weight losses corresponding to the loss of interparticle water, interlayer water, and dehydroxylation of the hydroxide layers and decarbonation of the interlayer region.     

Crystal growth kinetics in BaOAl2O32SiO2 and SrOAl2O32SiO2 glasses

Crystallization kinetics of BaOAl₂O₃2Si0₂ (BAS) and SrOAl₂O₃2SiO₂ (SAS) glasses in bulk and powderforms have been studied by non-isothermal differential scanning calorimetry (DSC). The crystal growth activation energies were evaluated to be 473 and 451 kJ mol^–1 for bulk samples and 560 and 534 kJ mol^–1 for powder specimens in BAS and SAS glasses, respectively. Development of crystalline phases on thermal treatments of glasses at various temperatures has been followed by powder X-ray diffraction. Powder samples crystallized at lower temperatures than the bulk and the crystallization temperature was lower for SAS glass than BAS. Crystallization in both glasses appeared to be surface nucleated. The high temperature phase hexacelsian, MAl₂Si₂O₈ (M = Ba or Sr), crystallized first by nucleating preferentially on the glass surface. Also, monoclinic celsian does not nucleate directly in the glass, but is formed at higher temperatures from the transformation of the metastable hexagonal phase. In SAS the transformation to monoclinic celsian occurred rapidly after 1 h at 1100 °C. In contrast, in BAS this transformation is sluggish and difficult and did not go to completion even after 10 h heat treatment at 1400 °C. The crystal growth morphologies in the glasses have been observed by optical microscopy. Some of the physical properties of the two glasses are also reported.     

Structural investigation of rapidly quenched Li3BO3−Li4GeO4 glasses

Glasses were prepared in the pseudobinary system Li₃B0₃–Li₄GeO₄ by a rapid quenching technique in the composition range of 8–80 mol% Li₄GeO₄. The structure of the glasses was examined by Raman spectra, X-ray diffraction analysis and molecular dynamics simulation. The coordination number of germanium atoms with respect to oxygen atoms in the glasses Li₃B0₃–Li₄GeO₄ was shown to be higher than four by the X-ray diffraction analysis. The Raman spectra showed that not only monomer ions of BO ₃ ^–3 and GeO ₄ ^–4 , but also dimer B₂O ₅ ^–4 ions and six-coordinated GeO ₆ ^–8 ions were present in these glasses over the whole glass-forming region. The presence of these ions was also confirmed from molecular dynamics simulation.     

Oxide impurity absorptions in Ge-Se-Te glass fibres

Oxide impurity absorptions in Ge-Se-Te glass fibres and the cause of the absorption loss around 943 cm^–1, the frequency of the CO² laser, have been investigated. The oxygen in the glass bounds preferentially to germanium and causes the absorptions due to Ge-O bond vibrations at 765 cm^–1 (band I) and 1230cm^–1 (band II). The excess absorptions due to these bands were determined as 0.228cm^–1/P.p.m. wt O₂ for band-I and 0.006cm^–1 /p.p.m. wt O₂ for band II. The loss of the fibre at 943cm^–1 increased with the oxygen content. It was, however, revealed from the deconvolution of the IR spectra into the independent absorption components that the absorption tails of band I and band II did not affect the loss at 943 cm^–1. The content of the impurities except oxygen analysed by a mass spectroscopy was too low to affect the loss at 943 cm^–1.     

Electronic Raman scattering of superconducting YBa2Cu3Oy single crystals

TheA _1g andB _1g low-energy Raman continua of YBa₂Cu₃O _y (Y123) single crystals, withy=7.0, 6.99, and 6.93, have been investigated. It is found that the peak frequency of theA _1g continuum is equal to 310±10 cm^–1 and independent of oxygen concentration fory in the above range. The central frequency of the broad peak in theB _1g continuum, however, shifts from about 470 cm^–1 fory7.0 to 550 cm^–1 fory6.93. Thus, a relatively small change in oxygen concentration results in a significant redistribution of the states contributing to theB _1g continuum. Assuming the low-energy portions of the continua are electronic in origin, the Raman spectra have been calculated and the results compared to the experimental spectra. It is suggested that the Raman continua arise, at least in part, from scattering across a spin fluctuation-induced pseudogap.     

Coordination state of Nb5+ ions in silicate and gallate glasses as studied by Raman spectroscopy

Raman spectra of K₂O-Nb₂O₅-SiO₂ glasses are measured in order to compare the coordination state of Nb⁵⁺ ions in gallate glasses with that in silicate glasses. It is found that less-distorted NbO₆ octahedra with no non-bridging oxygens as well as NbO₆ octahedra with non-bridging oxygens and/or with much distortion are present in the K₂O-Nb₂O₅-SiO₂ glasses. The Raman band in the 800 to 900 cm^–1 region is attributed to the NbO₆ octahedra with non-bridging oxygens and/or with much distortion. The broad bands in the 600 to 800 cm^–1 region are attributed to less-distorted NbO₆ octahedra with no non-bridging oxygens. An increase in the molar ratio Nb₂O₅/K₂O leads to an increase in the oxygens shared by more than two polyhedra and/or a decrease in non-bridging oxygens for the NbO₆ octahedra which possess non-bridging oxygens, or to an increase of distortion for much-distorted NbO₆ octahedra. At the same time, an increase in the molar ratio Nb₂O₅/K₂O increases the less-distorted NbO₆ octahedra with no non-bridging oxygens. In short, GaO₄ tetrahedra and NbO₆ octahedra compete to attract alkali ions in gallate glasses but such competition is not found in silicate glasses.