Scattering losses in binary borate glasses

The purpose of this paper is to examine the potential of three binary borate glasses; namely PbOB₂O₃, K₂OB₂O₃ and Li₂OB₂O₃ as candidates for fabrication of low optical loss and low cost fiber-glass wave-guides.The importance of ultrasonic measurements as the first step in a systematic search for a glass with low optical loss, is discussed. Results of ultrasonic measurements of PbOB₂O₃ system are then presented. Using these results and the published results for the K₂OB₂O₃ and Li₂OB₂O₃ systems, estimates of the magnitude of density fluctuations as a function of composition have been made for each system. Comparison with the previously published results on the K₂OSiO₂ system suggests that out of the three systems chosen, only 50 mole % Li₂O50 mole % B₂O₃ glass is a likely candidate for the production of low optical loss glass fibers.     

Fluoride glasses in the ZrF4BaF2YF3AlF3 quaternary system

The quaternary system ZrF₄BaF₂YF₃AlF₃ has been investigated in order to determine the nature of the vitreous domain. Addition of aluminium fluoride to the basic ZrF₄BaF₂YF₃ ternary system results in an increase in the size of the vitreous area and a lowering of the crystallization rate.The change of density, refractive index and T_G with respect to composition has been studied. It has been shown that the substitution of Zr⁴⁺/Al³⁺ involves a change in the cationic distribution rather than in the anionic packing.     

Pressure effects on electrical conduction in glasses

Electrical conduction in various inorganic glasses was studied as a function of hydrostatic pressure up to 2000 atm and phenomenologically classified into electronic, ionic and mixed types. In electronically conducting glasses such as AsSe chalcogenide glasses and Fe₂O₃P₂O₅ glass, the conduction is enhanced by application of pressure. On the other hand in ionically conducting glass such as Na₂OB₂O₃ glass, the conduction is suppressed through the concept of an activation volume. The compatibility of electronic and ionic conduction processes in glasses such as Ag-doped AsSe glasses and Bi₂O₃B₂O₃ glass, which have more complex conduction processes, was discussed from these aspects.     

Defect species in vitreous silica - a molecular dynamics simulation

The properties of overcoordinated defect species in vitreous silica were analyzed using the molecular dynamics computer simulation technique. The defect species are 3-fold- oxygen and 5-fold silicon. Frequency spectra, SiOSi bond angle distribution, and SiO bond lengths are presented for normally coordinated species and for defect species. Results indicate the presence of the C₃⁺ defect in vitreous silica. Also, a compression of the SiOSi bond angle and an expansion in the SiO bond length occur for the C₃⁺ oxygen defect.     

On the compositional dependence of the optical gap in amorphous semiconducting alloys

It is found that the optical gap E_AB for amorphous A-B alloys can be determined by the energy gap E_A for element A and E_AB for the element B in the equation E_AB(Y) = YE_A + (1?Y) E_B where Y is the volume fraction of element A. Calculations based on a random bond network agree with experiments for SiGe, SbSe, and AsTe films (class A). Calculations based on a chemically ordered bond network which tends to form microscopic molecular species gree with experimental results for the AsSe, AsS, GeTe and Sb₂Se₃As₂Se₃ systems (class B). In contrast to the above systems, agreement with experiment is not obtained for the TeSe, As₂Te₃As₂Se₃ and GeTe₂GeSe₂ systems which contain atoms of both Te and Se (class C). The classification into three types (classes A, B and C) is consistent with the calculation based on effective medium percolation theory which interprets the compositional dependence of the conductivity of chalcogenide glasses.     

Fracture toughness-composition relationship in some binary and ternary glass systems

Measurements of the critical stress intensity factor K_Ic are reported for glasses in the Na₂OSiO₂, PbOSiO₂, ZnOB₂O₃, PbOB₂O₃, Na₂OGeO₂ and 20Na₂O?(80 ? x) B₂O₃ ? xSiO₂ systems. The variations of K_Ic with composition are not directly related to the simultaneous variations of Young's modulus. A tentative interpretation is given.     

Study on local structure in amorphous SbS films by Raman scattering

A stoichiometric Sb₄₀S₆₀ film contains SbSb and SS bonds in addition to SbS bonds in an SbS₃ unit. The amount of the SbSb bond rapidly decreases with an increase in the S content beyond the stoichiometric value. On the other hand, as the S content decrease beyond the stoichiometric value, the SbS bond decreases and the SbSb bond increases. Annealing at temperatures near the glass transition decreases the fraction of the SbSb bond in the Sb₄₀S₆₀ film.     

Observations of the behaviour of some thin film cathodes in the scanning electron microscope

The tope electrodes of silver or copper from which electron emission occurs, are studied for M-I-M structures of AgSiO/B[₂]O₃Cu and AgSiO/B₂O₃Ag while the specimens are contained in the chamber of a scanning electron microscope and subjected to bias voltages. Electroforming of the samples and their subsequent operation as negative resistance and electron-emitting devices lead to characteristic disturbances of the top electrodes which are consistent with the idea of filamentary conduction processes.     

NMR studies on rapidly solidified SiO2Al2O3 and SiO2Al2O3Na2O-glasses

²⁷Al and ²⁹Si MAS NMR studies were performed on roller-quenched SiO₂Al₂O₃-glasses with Al₂O₃ contents ranging from 10 to 60 mol% and on SiO₂Al₂O₃Na₂O glasses containing 10 mol% Al₂O₃ and 2.5 to 10 mol% Na₂O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO₂Al₂O₃Na₂O the 30 ppm peak decreases to zero as the Na₂O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al₂O₃ over Na₂O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na₂O.     

Thermoelectric power of AsSeTe glasses

The result of the measurement of the thermoelectric power of glasses in the As₂Se₃As₂Te₃ system are reported. The results indicate that towards the As₂Te₃ end of the composition, there is an anomalous increase in thermoelectric power, the origin of which is not clear. Polaron hopping seems to contribute to conductivity in tellurium rich glasses. Structural restrictions on polaron hopping, such as the availability of AsTeAsTe chains seems to be important in discussing transport behaviour.     

Raman study of the structure of glasses along the join SiO2GeO2

In order to better understand the distribution of tetrahedra in multicomponent tetrahedral network structures of melts and glasses, we have investigated the Raman spectra of binary SiO₂GeO₂ glasses. We compare the Raman spectral features of the end-member glasses and discuss their vibrational origins. The mixing of GeO₂ and SiO₂ melts results in a continuous random network structure of TO₄ tetrahedra (T  Si, Ge) in the glass. Raman bands corresponding to the asymmetric stretch (v_as) of oxygen in GeOGe, SiOSi and SiOGe bonds are observed in the glasses having intermediate compositions along the SiO₂GeO₂ join. The presence of three distinct v_as (TOT) bands in the spectrum of a glass having Si/Ge one reveals that a considerable degree of SiGe disorder exists in the glass. The presence of a single symmetric oxygen stretching band in the spectra of binary SiO₂GeO₂ glasses indicates that the symmetric stretch modes (v_s) of oxygen in SiOSi, SiOGe and GeOGe bonds are strongly coupled. An observed decrease in the halfwidth of the v_s (TOT) band in the spectra of SiO₂GeO₂ glasses with increasing concentration of GeO₂ may be attributed to a decrease in the average TOT bond angle and a predominance of six-membered ring structures. Results of the present study support the assignment of the bands in the 900–1200 cm^?1 region of the alumino-silicate glasses, spectra to the v_as(AlOSi) and v_as(SiOSi) modes. In contrast to the alumino-silicate glasses, however, the SiO₂GeO₂ glasses have a much higher degree of disorder of the network-forming cations.     

An application of MNDO calculation to borate polyhedra

MNDO, a semiempirical SCF-MO method, was applied to study the structure of the borate glass. The clusters, B(OH)₃, H₃B₃O₆, B₃O₆^3?, (HO)₂BOB (OH)₂, (HO)₂B₃O₃OB₃O₃ (OH)₂, BO₃[B(OH)₂]₃ and BO₃[B₃O₃(OH)₂]₃ were treated and their geometries, the heats of reactions, the π electron systems and electronic structures were discussed. The geometry and the electronic structures show a good correspondence with the experimental data. The resonance stabilization effect of the π electron system is not so large as to control the geometries and reactions.     

Stabilization of heavy metals fluoride glasses

A new class of fluoride glasses has been isolated in the ternary system containing one transition metal fluoride ZnF₂, one rare earth fluoride YbF₃ and one actinide fluoride ThF₄. The controlled addition of BaF₂ playing the role of modifier allows the stabilization of glasses with low rate of crystallization in the quaternary system BaF₂ThF₄ZnF₂YbF₃. The infrared transmission can be extended to the 7–8 μ region, a significant improvement over the fluorozirconate glasses.     

Vibrational spectra of vapor-deposited binary phosphosilicate glasses

Room temperature infrared transmission spectra in the range 4000-250 cm^?1 of binary phosphosilicate glass (PSG) films deposited by reacting argon- or nitrogen-diluted PH₃SiH₄O₂ mixtures on heated silicon substrates at 300–400° C have been obtained across the whole composition range. In all the as-deposited binary films, an absorption at ≈1300 cm^?1 characteristics of the P=O vibration was found to persist, together with a couple of broad absorptions in the regions 1200-900 cm^?1 and 500 cm^?1. Using a differential infrared technique the broad feature in the higher frequency region has been resolved into two well-defined bands at ≈1100 and 970 cm^?1. A detailed analysis shows that the intensity variation of the differential band at ≈1100 cm^?1 conforms well, at least to 50 mol% P₂O₅, to a simple structural model that yields an analytic distribution of POSi linkages as a function of composition by assuming chemical mixing in the vapor-deposited P₂O₅SiO₂ system. Furthermore, the system may be written as (P=O)₂ O₃SiO₂ in order to emphasize the similarity of its coordination scheme with that of the B₂O₃SiO₂ system studied earlier. The nature of these CVD films has also been elucidated by thermal and water treatments.     

Brillouin scattering measurements of attenuation and velocity of hypersounds in SiO2B2O3 glasses

Measurements of hypersound wave velocity and attenuation (20–30 GHz) were made at room temperature by Brillouin scattering in SiO₂O₂O₃ glasses. The attenuation shows a maximum with composition. An explanation of this maximum is given in relation to the glass structure. It is thought that this maximum may be due to a coupling effect of hypersounds with structural relaxational process involving SiSi and SiOB bonds.     

Raman spectroscopic investigation of the structure of silicate glasses (II). Soda-alkaline earth-alumina ternary and quaternary glasses

Raman spectra of some ternary and quaternary glasses in the system Na₂OCaOMgOAl₂O₃SiO₂ are presented. The spectra are interpreted in terms of the structural alteration of the glass as the composition is altered from the binary end members to more complicated glasses. Addition of CaO and MgO to soda-silica glasses act only to increase the disorder of the network slightly. Addition of Al₂O₃ greatly modifies the network. In some soda-lime-aluminosiliscate compositions an estimate can be made of the amount of aluminum in four- and six-fold coordination. It is shown that the amounts of four- and sixfold coordinated aluminum depend on the glass composition.     

Rare earths in fluoride glasses: The LnF3AlF3ThF4BaF2 systems and related glasses

Glass compositions have been investigated in the BaF₂AlF₃ThF₄LnF₃ systems (Ln = rare earths or Y). Glasses have been obtained for the compositions 0.2 BaF₂, 0.3 AlF₃, 0.2 ThF₄, 0.3 LnF₃ and 0.3 BaF₂, 0.3 AlF₃, 0.2 ThF₄, 0.2 LnF₃ for the rare earths heavier than samarium. The glassy transition occurs near 450°C and fusion near 750°C; the density is between 5 and 6 and refractive index between 1.48 and 1.50. Large amounts of alkali fluorides (LiF, NaF, KF) may be included in the glass composition. The glassy area has been drawn in the pseudo-ternary system NaF(Al_0.5Y_0.5)F₃(Ba_0.5Th_0.5)F₃. Alkali incorporation leads to a decrease of the characteristic temperatures. Numerous new glassy compositions are given deriving from the basic ternary or quaternary systems with the addition of alkali fluoride, MgF₂ and CaF₂.     

Structure and properties of silver phosphate glasses — Infrared and visible spectra

The infrared and visible spectra of glasses in the Ag₂OP₂O₅ glass-forming system were obtained. The infrared data were interpreted as indicating the presence of polymeric chains in these glasses. The partial covalent nature of the AgOP bond was discussed. A mixed NaPO₃AgPO₃ glass showed no unexpected bands in the infrared spectrum, again showing that silver is behaving in a manner similar to alkali metal ions in phosphate glasses. The shift in the absorption edge in the visible spectra of glasses of different Ag/P ratio was shown to arise from either an increase in the concentration of nonbridging oxygens with increasing silver content, or the presence of colloidal silver metal particles.     

Polynary silicon arsenic chalcogenide glasses with high softening temperatures

The introduction of Ag in SiAsTe glasses permits the incorporation of Se, otherwise volatile and/or degradable as a constituent in Si-containing chalcogenide glasses. SiAsAgTeSe glasses exhibit much higher softening ranges and glass transition temperatures than encountered in known chalgogenide systems. A glass Si₃₅As₁₅Ag₁₀Te₂₀Se₂₀ had the viscosity log ν = 13 at about 500°C, as compared to 370°C for the base glass Si₃₅As₂₅Te₄₀, the viscosity of log ν = 9.8 at about 560°C, as compared to 442°C for the base glass. Phase separation occurs in the system SiAsAgTeSe and becomes manifest in two glass transitions indicated by changes in the slopes of the expansion curves and breaks in the softening point-composition relations. The existence and behavior SiAsAgTeSe glasses suggests the possible development of higher T_g i.r. transparencies and higher T_g semiconductor glasses than described so far.     

X-ray diffraction studies of glasses in the systems Na2OMeOSiO2 (MeMg,Zn, Ca,Ba)

X-ray diffraction studies of glasses in the following ternary systems have been made: Na₂OMgOSiO₂, Na₂OZnOSiO₂, Na₂OCaOSiO₂ and Na₂OBaOSiO₂. The following heavy atom substitutions have been used: Ag for Na and Ge for Si. The changes in the electron radial distribution curves resulting from AgNa replacement can be explained as amplifications of relatively well-defined NaSi distances, which are nearly the same in all the glasses investigated. The GeSi substitution causes changes which can be explained on the basis of isostructural GeSi substitutions.