Optical absorption and elastic properties of Li2O---(LiCl)2---B2O3---Al2O3 glasses

Ultraviolet transmission, densities, and supersonic velocities of the Li₂O---(LiCl)₂---B₂O₃---Al₂O₃ glasses were measured. Adiabatic compressibilities of all these glasses were calculated. The results were interpreted from the viewpoint of the glass structure.     

Study on phase diagram of Bi2O3---SiO2 system for Bridgman growth of Bi4Si3O12 single crystal

Phase relation of Bi₂O₃---SiO₂ system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi₂SiO₅ in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi₂SiO₅ crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm³ was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO.     

Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO₃–Fe₂O₃–P₂O₅ and one series of SrO–Fe₂O₃–P₂O₅ glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO₃ is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe₂O₃ content and Fe(II)/Fe_tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe₂O₃ content in MoO₃–Fe₂O₃–P₂O₅ glasses with O/P at 3.5 the dc conductivity, σ_dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe₂O₃ and is independent of the MoO₃ content. Also, the dielectric properties such as ^′(ω), ^″(ω) and σ_ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO₃. On the other hand, the dc conductivity for MoO₃–Fe₂O₃–P₂O₅ glasses with O/P > 3.5 increases with the substitution of MoO₃ which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ^′(ω) with increasing MoO₃ content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe₂O₃–P₂O₅ glasses the conductivity and dielectric permittivity remained constant with increasing SrO.     

The short-range order in ternary ZrF4---BaF2---ErF3 glasses

The short-range order structures in ternary ZrF₄---BaF₂---ErF₃ glasses have been studied by X-ray absorption fine structure (XAFS). The near-neighbor structures around Zr, Ba and Er have been determined and compared with that in binary ZrF₄---BaF₂ glasses. The near-neighbor structures around Zr and Ba are scarcely affected by doping with ErF₃. The structural parameters of near neighbors around Er in the glasses are near to that in ErF₃, but the corresponding distance and coordination number of near neighbors in the glasses decrease slightly. It is also observed that the intensities of the white lines at the Er L and L absorption edges in these glasses are different from that in c-ErF₃. Meanwhile, compared with that of the corresponding fluoride, the changes of the ‘white line’ at the Er L_,-edges in the glasses differ from the case of Nd. The causes leading to these differences are discussed.     

Chemical strengthening of Na2O---Al2O3---SiO2 system glasses by surface controlled crystallization

Appropriate glass compositions of the Na₂O---Al₂O₃---SiO₂ system and glass melting technology were investigated. The dependence of some factors, such as composition of molten salts, time and temperature of ion exchange treatment on the modulus of rupture was studied. As expected, the coefficient of interdiffusion is a function of concentration and has the mixed-alkali effect. The order of the interdiffusion coefficient is 10⁻⁶ cm²/s. The effect of binary and ternary salt baths on the surface controlled crystallization was reported. The experimental data showed that there is a series of technological advantages from applying molten salts of the ternary system Li₂SO₄---Na₂SO₄---K₂SO₄ in comparison with the binary system Li₂SO₄---Na₂SO₄.     

Viscosity and IR investigations in the Li2O---B2O3 system

The high viscosity in melts of the Li₂O---B₂O₃ system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li₂O---B₂O₃ system are reported in this paper. When the temperature increases the viscosity of li₂O---B₂O₃ system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li₂O---B₂O₃ melts, the viscosity rises gradually to a maximum with a composition Li₂O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na₂O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li₂O---B₂O₃ samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li₂O---B₂O₃ system. For Li₂O: 4.513203, an ideal additive agent is 20wt% Li₂O:: 2MoO₃. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li₂O---B₂O₃ system revealed that the BO₄⁻/NO₃⁻ ratio is reduced in the melt using Li₂O: 2MoO₃ as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO₄⁻. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears.     

Study of crystallisation of the Li2O---ZnO---Al2O3---SiO2 system glasses

This paper deals with the relationship between phase separation and crystal morphology in the Li₂O---ZnO---Al₂O₃---SiO₂ system glasses, and investigates the effect of the nucleating agent on the microstructure of glass-ceramics, and the effects of heat treatment temperature on the properties of the microstructure.     

Silicate groupings in glassy and crystalline 2PbO·SiO2

The type and the amount of silicate groupings existing in glassy and crystalline 2PbO·SiO₂ have been determined by direct chemical methods: paper chromatography, trimethylsilylation combined with gas-liquid partition chromatography and by the molybdate method. The results obtained by these three different methods are in good agreement and demonstrate, that glassy 2PbO·SiO₂ and each of the three main crystalline polymorphs are characterized by its own specific silicate anion distribution: the distribution in vitreous 2PbO·SiO₂ is of a polyanionic nature; in T---Pb₂SiO₄ dimetic groups [Si₂O₇]⁶⁻ prevail; M₁---Pb₂SiO₄ contains predominantly [Si₄O₁₂]⁸⁻ rings and H---Pb₂SiO₄ is a typical polysilicate with chain anions [SiO₃²⁻]_n. The results fit a structural model according to which glass is a random array of discrete polyatomic groupings; the gradual transition from the glassy state to the stablest crystalline structure is connected with degradation and polymerization of silicate anions.     

Some characteristics of glass in the Al2O3---B2O3---SiO2 system from the gel

The colorless and transparent glasses in the Al₂O₃---B₂O₃---SiO₃ system with high B₂O₃ and SiO₂ content were prepared from gels at low temperature. Their IR spectra not only revealed the evolution of the gel to glass conversion, but also showed that the formation of mixed bonds in the glasses obtained did not show any effect due to the B₂O₃ content. The accuracy of the glass composition is dependent upon the SiO₂/B₂O₃ molar ratio. The higher the ratio, the less the deviation of the analyzed compositions of the resulting glasses from their original calculated values. It is obvious that the higher the ratio, the lower the thermal expansion coefficient and the higher the transformation temperature of the glass, and the temperature at which the thermal contraction reaches an equilibrium is higher.     

Flux growth of BPO4 crystals

Single crystals of BPO₄ with sizes up to 15×10×12 mm³ were grown by top-seeded solution growth method using Li₂O–Li₄P₂O₇ as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO₄ was about 130 nm. Its density was 2.82 g/cm³ determined using drainage method.     

Fast and slow dynamics in single and mixed alkali silicate glasses

A molecular dynamics (MD) simulation for single and mixed alkali metasilicates has been performed. The mixed alkali effect (MAE) in the diffusion coefficients is reproduced. The motion of lithium ions in Li₂SiO₃ can be divided into slow (type A) and fast (type B) categories clearly in the glassy state. It turns out that the slow dynamics are caused by localized jump motions with a long tail of the waiting time distribution. On the other hand, fast dynamics of the lithium ions are caused by successive cooperative jump motions and are identified as Lévy flights. The MAE in LiKSiO₃ occurs due to mutual interception of jump paths of both kinds of mobile ions. In such paths, the fast component is considerably suppressed. Namely, the cooperative forward-correlated jump process is sensitive to the blockage of the jump paths. Propagation of the immobilization in the MAE is discussed in relation with the mechanism of the cooperative jump motion. The ratio of the fast and slow dynamics plays an important role to determine the transport properties in the glassy state.     

Effect of Si3N4 on chemical durability of chalcogenide glass

Chemical durability of the Si₃N₄ doped (up to 0.5 wt%) chalconitride glasses was evaluated by weight losses of glass samples after immersion in deionized water, H₂SO₄, HCl and NaOH solutions. IR spectra and SEM were used as an aid to examine the surface structure of corroded glass samples. Weight loss measurements showed a poorer stability of non-oxide glasses in basic solution than in acid solution, and the Si₃N₄ doping was found to improve chemical durability. Comparison of IR spectra of samples exposed to the basic solution with their original ones suggested the higher content of OH⁻ in its reaction layers, indicating that the corrosion of the present non-oxide glasses in the basic solution may result from the breakdown of the bridging Se due to an attack launched by OH⁻. The SEM evidence confirmed that Si₃N₄ doping did hinder the OH⁻ attacks on Ge and/or As, which is most likely related to incorporation of the three-coordinated N into the glass network, as supported by a comparison of the IR transmitting spectrum between uncorroded chalconitride glass and undoped chalcogenide glass.     

Preparation and physical properties of amorphous V2O5 containing TiO2, Na2O or Li2O

V₂O₅ gels containing up to 18 mol% of TiO₂ were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V₂O₅ gels containing Na₂O or Li₂O were obtained through the ion exchange method. The crystallization temperature, T_cr, of the gels increased and the H₂O content of the gels decreased by the addition of TiO₂ or Na₂O. These additives seem to stabilize the amorphous state of the gels. On the other hand, T_cr and the H₂O-content slightly varied with the addition of Li₂O. No ionic polarization was observed in coating films of the gels dried at temperatures below T_cr. The dc conductivity of the films was anisotropic, and increased with the addition of Li₂O or Na₂O. However, it decreased with increasing TiO₂ content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method.     

Ab initio study of NMR spectra of Li2S–SiS2 glass system

We obtained the chemical shielding constants of ²⁹Si in Li₂S–SiS₂ glass system on the basis of molecular orbital calculations. The relative chemical shieldings calculated at the HF/6-31G* level is −16.1 and −23.8 ppm for E(1) and E(0), respectively. These calculations are in good agreement with the previous NMR study: σ(E(2))>σ(E(1))>σ(E(0)). It is found theoretically that incorporation of Li₂S into SiS₂ does not influence the ²⁹Si chemical shift, while incorporation of Li₂O into SiO₂ does to a significant extent. It is also found that the existence of oxygen in Li₂S–SiS₂ glasses increases the chemical shielding of ²⁹Si by about 25 ppm, which is in good agreement with the experimental result.     

Short-range order in RE4Al3 metallic glasses (RE = Pr, Gd, Tb, Dy)

A suitable model structure of RE₄Al₃ metallic glasses (RE = Pr, Gd, Tb, Dy) has been selected by comparing experimental pair correlation functions with model pair correlation functions for disordered crystal structures. A non-linear least-squares profile analysis of the experimental pair correlation functions has been performed with the use of the characteristic structural parameters of the model structure as variable parameters. The partial atomic distances and the partial coordination numbers have been estimated on the basis of the best fitting parameters. It is established that the local atomic arrangement in RE₄Al₃ metallic glasses resembles that in tetrahedrally close-packed Zr₄Al₃-type crystalline compounds.     

A glass-forming system with compound-forming tendency: As4S6---P4S10

Glasses in the quasi-binary system (As₄S₆)_x(P₄S₁₀)_1−x x = 0.1, …, 1.0, are produced and studied by thermal analysis, X-ray, and Raman spectroscopy. The phase diagram of the system and the critical cooling rate for glass formation both have their maximum at x = 0.5, corresponding to the compound As₂P₂S₈; the X-ray structure of recrystallized samples can be described as a sum of the As₂P₂S₈ (x = 0.5)- and the P₄S₁₀-structure (As₄S₆ not visible); Raman spectra of the glasses are again sums of As₂P₂S₈- and As₄S₆/P₄S₁₀-spectra. All these observations support the assumption that a stable building block corresponding to the 1:1 compound As₂P₂S₈ and surplus As₄S₆ (or P₄₁₀) are the essential elements of the structure in the glasses.     

Diffraction study of Li2O·SiO2 glass with computer simulation

The structure of Li₂O·SiO₂ glass has been determined by the pair-function analysis of the radial distribution function (RDF) obtained by X-ray and neutron diffraction measurements. The structure models were constructed by the molecular dynamics method (MD). The calculated RDFs, the summation of the pair-functions of the model, were compared with the observed RDFs while varying the MD parameters. Taking advantage of the negative scattering length of Li for neutron diffraction, the glass structure was investigated in detail, and it was found that the chains of SiO₄ tetrahedra bend at 20 °, which is a little less than for the crystal (23.48 °). It is known that the larger the size of the alkali ions (Na⁺ → K⁺ → Cs⁺), the smaller the bending angle of the chains. It was found that this rule also applies to Li⁺.     

Static B NMR studies of the short range order in alkali metal modified B2S3 glasses

The ¹¹B NMR spectra of xRb₂S+(1−x)B₂S₃ glasses in the range 0x0.75 and of xCs₂S+(1−x)B₂S₃ glasses in the range 0x0.60 are reported. The addition of Rb₂S to B₂S₃ creates on average approximately two and one-half tetrahedral borons for each added sulfur ion, whereas it is found that the addition of Cs₂S creates approximately 2 tetrahedral borons for each added sulfur ion. This behavior while more similar to that seen in the alkali borate glasses, contrasts that seen in the Na and K thioborate glasses, where six to eight and three, respectively, tetrahedral borons are formed for every sulfide anion added to the glass. These findings are supported by the IR and ¹¹B NMR spectra of the di-thioborate polycrystals (c-Rb₂S:2B₂S₃ and c-Cs₂S:2B₂S₃) whose structures appear to be comprised of two BS₄ tetrahedrals and two BS₃ trigonals (N₄0.5) like that in the alkali di-borate phases for both Rb and Cs. Unlike the ¹¹B NMR resonances of the sodium thioborate glasses where a single sharp line is observed for the tetrahedral boron site and a single quadrupolar broadened line is observed for all the trigonal sites, a third resonance line is observed at high alkali fractions for the rubidium and cesium thioborate glasses. This new structural feature may arise from asymmetric MBS₂ (meta-thioborate groups) or tetrahedral boron groups possessing a non-bridging sulfur.     

Structure and properties of the pure and Pr-doped Ge25Ga5Se70 and Ge30Ga5Se65 glasses

The Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ pure and Pr³⁺-doped glasses were prepared by direct synthesis from elements and PrCl₃. It was found that up to 1 mol% PrCl₃ can be introduced in the Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ glasses. Both types of glasses with overstoichiometric and substoichiometric content of Se were homogeneous and of black color. The optical energy gap is E^opt_g=2.10 eV, and the glass transition temperature is T_g=543 K for Ge₂₅Ga₅Se₇₀ and T_g=633 K for Ge₃₀Ga₅Se₆₅. The long-wavelength absorption edge is near 14 μm and it corresponds to multiphonon processes. Doping by Pr³⁺ ions creates absorption bands in transmission spectra, which can be assigned to the electron transitions from the ground ³H₄ level to the higher energy levels of Pr³⁺ ions ³H₅, ³H₆, ³F₂, ³F₃ and ³F₄, respectively. By excitation with YAG:Nd laser line (1064 nm), two intense luminescence bands (1343 and 1601 nm) were excited. The first band can be ascribed to electron transitions between ¹G₄ and ³H₅ energy levels of Pr³⁺ ions. Full width at half of maximum (FWHM) of the intensity of luminescence was found to be 70 nm for (Ge₂₅Ga₅Se₇₀)_1 − x(PrCl₃)_x and (Ge₃₀Ga₅Se₆₅)_1 − x(PrCl₃)_x glasses. The FWHM in selenide glasses is lower than in halide and sulphide glasses. The second luminescence band (1601 nm) can be probably ascribed to the transitions between ³F₃ and ³H₄ energy levels of Pr³⁺ ions. The absorption and luminescence spectra of Pr³⁺ ions in studied glasses are slightly influenced by stoichiometry of glassy matrix. The Raman spectra of studied glasses were deconvoluted and assignment of Raman bands to individual vibration modes of basic structural units was suggested. The structure of studied glasses is mainly formed by corner-sharing and edge-sharing GeSe₄ tetrahedra. The vibration modes of Ga-containing structural units were not found, they are apparently overlapping with Ge-containing structural units due to small difference between atomic weights of Ge and Ga. In the glasses with substoichiometry of Se, the Ge–Ge bonds of Ge₂Se₆ structural units were found. In Se-rich glasses the Se–Se vibration modes were found. In all studied glasses also ‘wrong' bonds between like atoms were found in small amounts. Maximum phonon energy of studied glasses is 320 cm⁻¹.     

Raman spectrum studies of the glasses in the system Na2O---Al2O3---P2O5

Raman spectra of ternary sodium aluminosphosphate glasses indicate that for glasses with Al₂O₃/P₂O₅<0.63, the glass network is mainly built up of (PO₃)_n^n- chains and rings or different kinds of phosphate groups and AlO₄ tetrahedra; for glasses with Al₂O₃/P₂O₅>0.63, the glass network is mainly built up of AlPO₄ groups.