Structure of binary neodymium borate glasses by infrared spectroscopy

Using fast roller quenching techniques, a new series of binary rare earth oxide borate glasses were synthesized, with general formula xNd₂O₃ + (1 − x)B₂O₃, where x varies up to 35 mol%. The glasses were investigated by using mid infrared reflectance spectroscopy. The results show that the neodymium acts as a modifier, similar to an alkali metal. As x is increased, the borate glass network is shown to change from a three-coordinated to four-coordinated boron system. The results are further investigated by analyzing the spectra in terms of the location of the bands to show how the borate groups change upon neodymium addition.     

Study of thermal and optical properties of the Ge-Te-CdI2/ZnI2 far infrared transmitting glasses

A systematic series of (100 ? x)(GeTe_4.3) ? xCdI₂/ZnI₂ far infrared transmitting glasses were prepared by traditional melt-quenching method. ZnI₂ (20 mol%) can be introduced in the glassy matrix, while only 10 mol% CdI₂ can be incorporated in the Ge-Te-CdI₂ glass system. Based on differential thermal analysis (DTA) data, most of the glass samples have good thermal stability. A maximum ΔT value of 115 °C was obtained for the glass composition 90(GeTe_4.3)–10ZnI₂. The allowed indirect transition optical band gap was calculated according to the classical Tauc equation. It is found that the indirect optical band gap decreased from 0.619 to 0.569 eV with the CdI₂ addition and increased from 0.628 to 0.677 eV with the ZnI₂ addition. According to infrared transmission spectra, the Ge-Te-CdI₂/ZnI₂ glasses show wide IR transparency.     

Vibrational spectroscopy study of niobium germanosilicate glasses

A series of glasses in the (Ge,Si)O₂–Nb₂O₅–(Na,K)₂O system were prepared by melting and casting. Their density and characteristic temperatures were determined by Differential Thermal Analysis (DTA) and their structure was analyzed by infrared and polarized Raman spectroscopies. DTA data have indicated an increased glass thermal stability with the replacement of GeO₂ by SiO₂. Kramers–Kronig analysis of the infrared specular reflectance data indicated a strong ionic character for the germanosilicate glasses. The Raman spectra of germanosilicate compositions were generally dominated by an intense Boson peak at ∼72 cm⁻¹ and a high frequency, polarised peak at ∼880 cm⁻¹, related to NbO₆ octahedra with at least one non-bridging oxygen. The germanosilicate structure appears to be formed by alternating GeO₄ tetrahedra and NbO₆ octahedra, in addition to SiO₄ tetrahedra.     

Structure and lattice dynamics of binary lead silicate glasses investigated by infrared spectroscopy

The polar lattices dynamics of seven binary lead silicate glasses have been studied by infrared spectroscopy. The analysis of the reflectivity spectra with a dielectric function model, based on a modified Gaussian profile, allows a quantitative evaluation of the presence of lead cations within different structural sites. From the role of the lead cations versus the degree of polymerization of the silicate network and the comparison with literature results, we may to give a scenario for explaining the observed structural evolution of the glass matrix and more particularly the drastic change occurring around 45% of lead content. Below this threshold, lead cations act only as modifiers of the silicate network. Above, the glass structure is deeply modified; a lead network involving around 10% of the lead content appears in glasses whose composition is just above the threshold and progressively grows at the expense of the silicate network with the increase of lead content. For high lead content, lead cations can act as modifiers of the silicate network or as network formers. Results also show that the analysis of far infrared measurements combined with the knowledge of the UV edge optical response is very promising to characterize the local disorder around cations in glasses.     

An infrared study of crystallization in sodium-disilicate glasses containing iron oxides

The infrared absorption spectra of sodium-disilicate glasses containing various amounts of Fe₂O₃ ([Na₂O · 2 SiO₂]_1−x [Fe₂O₃]_x, where X = 0.05, 0.1 and 0.2) were investigated in the wavenumber range from 200–2000 cm⁻¹. The addition of Fe₂O₃ to the sodium-disilicate glass does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium-disilicate glass; nevertheless, a general shift of the existing absorption bands toward lower wavenumbers is observed. The amount of shift is, in fact, proportional to the content of Fe₂O₃ in the glass. This observation is consistent with the recently proposed structural model for the bonding of Fe³⁺ ions in the iron-sodium-silicate glass system.

Annealing of 20 mol% iron oxide glasses at 550 and 580°C produced an extra sharp infrared absorption peak at about 610 cm⁻¹ wavenumber. This new peak is believed to be related to the crystallized particles of the glass as concluded from both a scanning electron micrograph and an electron diffraction pattern.     

A new model for the structure of chalcogenide glasses: The closed cluster model

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As₂S₃.     

The interdependence of physical parameters for infrared transmitting glasses

Glasses based on sulfur and selenium were carefully characterized to establish the interdependence between chemical composition and the magnitudes of physical parameters related to their use as infrared optical materials. Parameters considered in this paper are density, volume-expansion coefficient, glass-transition temperature, thermal conductivity, elastic moduli, and Poisson's ratio.     

Terahertz spectroscopy of polar solute molecules in non-polar solvents

Low frequency spectra of liquid solutions of non-polar solvents were measured in the frequency range of 15–80 cm⁻¹ at room temperature by terahertz time-domain spectroscopy to investigate the solute–solvent interaction. The extinction coefficient of the solutions with polar solutes decreases as a function of frequency, whereas that of a non-polar solute increases. It is concluded that the observed spectral change of the polar solute is caused by fast reorientational dynamics due to librational motion of solutes.     

A new theoretical description for anomalous birefringence of phase-separated glasses

Theoretical relationships between anomalous birefringence and microstructure of phase-separated glasses are proposed based on light scattering by particles and self-consistent effective-medium theory. A phase-separated and stretched glass generally has positive anomalous birefringence because the positive birefringence produced by form anisotropy of the secondary phase particles is larger than the negative birefringence produced by the distribution anisotropy of the particles. A postpulling heat-treated glass has negative birefringence because the form anisotropy decays and the distribution anisotropy remains. The magnitude of the anomalous birefringence increasesin particle size, particle size distribution variance, volume fraction of secondary phase, and uniaxial load. Results obtained by the theoretical model are consistent with available experimental results.     

The structure of GeO2-SiO2 glasses and melts: A Raman spectroscopy study

We have investigated a series of glasses and melts along the GeO₂-SiO₂ join using insitu Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO₂-like, GeO₂-like and mixed GeO₂-SiO₂-like. Incorporation of GeO₂ into the SiO₂ network is initially accommodated via the 3- and 4-membered SiO₄ rings which are lost as they convert to larger mixed Ge/Si rings. The LO-TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO₄ rings and large SiO₄ rings; the small 3- and 4-membered SiO₄ rings are not reformed.     

An X-ray absorption spectroscopy study of the local environment of iron in degradable iron–phosphate glasses

Degradable iron–phosphate glasses with the composition of (CaO)_0.30–(Na₂O)_0.20?x–(Fe₂O₃)_x–(P₂O₅)_0.50, x = 0.01–0.05, were studied by Fe K-edge X-ray absorption spectroscopy (both near-edge, XANES, and extended, EXAFS). The addition of up to 5 mol% iron oxide is known to enhance the durability of the phosphate glass while maintaining biocompatibility. The results from the two techniques used here both show that iron is in the Fe(III) oxidation state and has octahedral coordination. This suggests that Fe is cross-linking the phosphate chains and therefore strengthening the network structure, resulting improved chemical durability of the glasses.     

Defect-mediated self-diffusion in calcium aluminosilicate glasses: A molecular modeling study

The mechanism of self-diffusion in calcium aluminosilicate glasses is investigated at the atomistic level using molecular dynamics (MD) simulations. We study nine glass compositions having the fixed ratio R = [CaO]/[Al₂O₃] = 1 and the concentration of SiO₂ varied from 11.8 to 76.5 mol%. The diffusion coefficient is calculated for each composition at different temperatures from 300 to 6000 K in steps of 300 K. The self-diffusivities of the various elements are found to be close to each other in magnitude, signifying the cooperative nature of the atomic movement. Network “defects” such as miscoordinated cations, non-bridging oxygen, and oxygen triclusters are also studied as a function of temperature and composition. We find that the behavior of self-diffusion correlates well with the concentration of network defects. A model of self-diffusion in calcium aluminosilicate glasses is proposed where diffusion is considered as a defect-mediated process resulting from bond-switching reactions at high temperature.     

Comment on “infrared spectroscopy of surfaces of glasses containing alkali ions” by R.H. Doremus

Absorption and fluorescene spectra and fluorescence lifetimes of Nd³⁺ ions were measured for the following polymeric metaphosphate glasses: [M(PO₃)₂]_n, where M = Mg, Ca, Sr, Ba, Zn, Cd, and Al(PO₃)₃. Judd-Ofelt intensity parameters for f-f transitions were derived from the integrated absorption spectra and used to calculate the spontaneous emission probabilities from the ${}^4\text{F}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ state. Metaphosphate glasses exhibit systematic variations of refractive indices, optical intensity parameters, fluorescence lifetimes and linewidths, and stimulated emission cross sections with alkaline earth. The origin of these variations and their implications for tailoring spectroscopic properties by compositional changes are discussed. Neodymium laser action in metaphosphate glasses is also considered.     

A multinuclear NMR study of sodium-borovanadophosphate glasses

xNaVO₃ · yNaPO₃ · (1 − y)NaBO₂ glasses were prepared where x = 0.0, 0.05, 0.5 and 0 ? y ? 1. These glasses have been investigated with multinuclear MAS NMR. ⁵¹V NMR spectra show that two vanadate configurations are possible, assigned as four and five coordinated vanadium. The concentration of the latter group decreases upon addition of sodium-borate. The presence of four and three coordinated boron sites can be deduced from the ¹¹B NMR spectra. The latter boron sites appear only when borate groups are connected to each other. ³¹P NMR spectra of borophosphates and borovanadophosphates show that the ratio of pyro- and metaphosphates is greater in the glasses containing vanadate than in simple borophosphates. These results indicate phosphate to be the most acidic agent and therefore the best chain-terminating group in these glasses.     

A Pb MAS-NMR study of Pb-containing glasses

²⁰⁷Pb magic angle spinning (MAS)-NMR spectra have been obtained for various Pb-containing crystalline compounds and high lead glasses. The isotropic chemical shifts were determined for the crystalline samples. The more ionic lead atoms with a coordination number larger than six had relatively small chemical shifts between 0 and 2382 ppm with respect to crystalline Pb(NO₃)₂. On the other hand, the covalent lead atoms with PbO₃ trigonal and PbO₄ square pyramidal configurations gave a multiplet line profile with shifts ranging from about 3000 to 6000 ppm. The lead atoms with different local environments in PbSiO₃ (alamosite) and H-Pb₂SiO₄, for instance, could be clearly distinguished from each other on the basis of the isotropic chemical shift. The NMR spectra for the high lead glasses of composition 67PbO·33SiO₂, 80PbO·20B₂O₃ and 70PbO· 30GaO_1.5 were found to exhibit an extremely broad peak with a shift ranging from about 3000 to 6000 ppm. This shift indicates that, in these glasses, neither such highly ionic lead atoms as found in symmetrical PbO₆ octahedra nor such highly covalent ones as found in PbO₄ square pyramids in the PbO crystal are predominant, but instead PbO₃ trigonal or PbO₄ square pyramids, with two or three other neighboring oxygens at larger distances as found in H-Pb₂SiO₄ or PbSiO₃, are the major lead-oxygen configuration.     

Structural study of thiosaccharin by single crystal X-ray diffraction and infrared spectroscopy

The structure of thiosaccharin (1,2-benzisothiazol-3(2H)-thione 1,1-dioxide) has been investigated by X-ray diffraction and infrared spectroscopic methods. The compound crystallizes in the orthorhombic space groupFdd2 witha=26.591(3),b=25.058(3),c=4.934(5) Å,Z=16. The structure consists of thiosaccharin molecules bonded to each other through N–H...O intermolecular hydrogen bonds. The infrared spectra of the thiosaccharin at room and liquid-nitrogen temperature were recorded. The spectral features in the N–H stretching region were correlated with the crystallographic data on the geometry of the N–H...O hydrogen bonding. In an attempt to assign the bands due to the SO₂ stretching modes, the spectrum of thiosaccharin was compared with that of saccharin (1,2-benzoisothiazole-3(2H)-one, 1,1-dioxide).     

A study of crystallization in some Li---Al---Si---O---N system glasses

The crystallization behavior of some Li---Al---Si---O---N system glasses under different conditions was studied. Experimental results show that the addition of nitrogen could decrease the crystallization tendency of glasses. In addition, the atmosphere, chemical composition and different sources of nitride could influence the crystallization of oxynitride glasses.