Mixed conductivity in tungstenite–phosphate glasses containing alkali metal ions

The conductivity of glasses in the 50WO₃–(50 ? x)P₂O₅–xA₂O (A = Na, K, Cs) system has been investigated as a function of composition. It is shown that in tungstenite–phosphate glasses containing different alkali metal ions the conductivity decreases with an increase in the alkali metal ion content. A decrease in conductivity is larger for heavier ions and reaches more than seven orders of magnitude in the case of glass containing Cs₂O. This behavior remains in contrast to the literature data on conductivity in transition metal oxide glasses containing alkali metal ions where usually strong conductivity anomalies of several orders of magnitude at certain amount of ions are observed. No necessity of ion–polaron interaction has been pointed out.     

Structural modifications induced by addition of copper oxide to lead–phosphate glasses

xCuO(1-x)[P₂O₅·PbO] glass system with 0 ≤ x ≤ 50 mol% was prepared and investigated by means of EPR and IR spectroscopy in order to evidence the structural changes induced by different amounts of copper ions. EPR spectra analysis together with EPR parameters has indicated a distorted tetragonal symmetry – named tetrahedral local symmetry – for Cu^2 + ions in the studied glasses. A change in the shape of EPR spectra was also observed as for small CuO concentration (x < 20 mol%) these glasses present an asymmetrical line typical for isolated ions and for high CuO content this line is replaced by a symmetrical one characteristic of clustered ions through dipole–dipole interactions. IR spectra of the studied glasses put in evidence a strong depolymerization effect with a gradual increase of CuO. The shift of PO asymmetric stretching vibration band to lower wave number can be explained by the increase of PO₄ tetrahedra charge density leading a more ionic and less covalent bonding.     

Broadband near-infrared emission from Bi–Er–Tm Co-doped germanate glasses

Bi–Er–Tm co-doped germanate glasses and Bi, Er, Tm singly doped glasses were prepared and characterized through absorption spectra, NIR emission spectra and decay lifetime. A super broadband near-infrared emission from 1000 nm to 1600 nm, covering the whole O, E, S, C, and L bands, was observed in the Bi–Er–Tm co-doped samples due to the result of the overlapping of the Bi related emission band (centered at 1300 nm), the emission from Er^{3+ 4}I_13/2 → ⁴I_15/2 transition (centered at 1534 nm) as well as the emission from Tm^{3+ 3}H₄ → ³F₄ transition (centered at 1440 nm), which is essential for broadly tunable laser sources and broadband optical amplifiers. The energy transfer process was also discussed at the end of the paper.     

Silver metal enhanced photoluminescence of Tm3+ doped GeS2–Ga2S3–CsCl glasses

We report silver metal enhanced near-IR and infrared-to-visible upconversion luminescence in Tm³⁺ doped 70GeS₂–10Ga₂S₃–20CsCl (in mol. %) glasses. The metal embedded glasses are prepared under controlled crystallization. Upon 808 nm excitation three fold enhancement of emissions is observed in the visible (446 nm, 496 nm, and 532 nm) and near infrared (1230 nm, 1450 nm and 1480 nm) regions. The possible mechanism responsible for the enhanced luminescence is discussed.     

New chalcohalide glasses from the GeS2–In2S3–CsCl system

New chalcohalide glasses from GeS₂–In₂S₃–CsCl pseudo-ternary system were prepared using the conventional melt-quenching method and its glass-forming region has been determined. The differences ΔT (T_P ? T_g) of partial glasses are large enough (>100 K) to permit the preparation of performs of considerable size. With the increased content of CsCl, the visible absorption edge (λ_vis) of these glasses indicates a distinct blue shift while a clear drop of their glass transition temperatures can be seen. The ultrafast non-linearity of partial glasses was measured using the Kerr shutter technique. The non-linear refractive index, n₂, was estimated to be in the magnitude of 10^?14 cm²/W. Widely transparent range, good glass-forming ability, higher χ⁽³⁾ and large electronic ultrafast OKE response make these glasses the potential applications in current photonic fields.     

UV–visible and infrared absorption spectra of transition metals-doped lead phosphate glasses and the effect of gamma irradiation

Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb²⁺). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb²⁺ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.     

Composition–structure–property relationships in boroaluminosilicate glasses

The complicated structural speciation in boroaluminosilicate glasses leads to a mixed network former effect yielding nonlinear variation in many macroscopic properties as a function of chemical composition. Here we study the composition–structure–property relationships in a series of sodium boroaluminosilicate glasses from peralkaline to peraluminous compositions by substituting Al₂O₃ for SiO₂. Our results reveal a pronounced change in all the measured physical properties (density, elastic moduli, hardness, glass transition temperature, and liquid fragility) around [Al₂O₃]–[Na₂O] = 0. The structural origin of this change is elucidated through nuclear magnetic resonance analyses and topological considerations. Furthermore, we find that addition of 1 mol% Fe₂O₃ exerts a complicated impact on the measured properties.     

Hardness and refractive index of Ca–Si–O–N glasses

Vickers hardness and refractive index was determined for Ca–Si–O–N glasses with 14.6–58 e/o N and 19–42 e/o Ca. By applying slow cooling rates, transparent glasses were obtained for compositions near Ca_9.94Si₁₀O_17.73N_8.14, while the majority of the glasses were opaque due to small inclusions of elemental Si and/or Ca-silicide. Determined glass densities varied between 2.80 and 3.25 g/cm³. Hardness was found to vary from 7.3 to 10.1 GPa at a load of 500 g and, respectively increase and decrease linearly with N and Ca content. The refractive index was found to increase linearly with N content from 1.62 to 1.95 and showed no significant dependence on Ca content.     

On the structure of tungstate–tellurite glasses

A continuous network model of xWO₃–(1 − x)TeO₂ glasses is developed, based on quantum-chemical calculation and Raman spectra analysis, in order to relate the structural and vibrational properties with glass composition. The tungstate–tellurite glass network is shown to be formed mainly by structural units of three types, TeO₄ trigonal bipyramids, OTeO₂ trigonal pyramids, and WO₆ octahedra with OW double bonds. Most of the W atoms are found to be incorporated into single OWO₅ octahedra, with no more than several percents of these atoms occurring in 2[OWO₅] paired tungstate centers. The structural and vibrational properties of tungstate–tellurite glasses of several compositions are analyzed by application of the model and a novel interpretation of the Raman spectra is suggested.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.     

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production,characterisation and thermal behaviour

The production of amorphous calcium silicate, CaSiO₃, by vacuum drying a sol–gel is described. The material exhibits a highly porous, irregular extended aggregate morphology. Its amorphous nature is confirmed by X-ray powder diffractometry and its silicate nature by vibrational spectroscopy. The latter is used to characterise the bridging/non-bridging oxygen distribution and hydration state, which comprises SiO₃ bonded hydroxyl and interstitial water. No indicators of silicon hydride defects were observed. From Raman/FTIR spectroscopy, the Si-O tetrahedral species are predominantly peaked around SiO₃^2?, as predicted by the stoichiometry of the starting materials. Variable temperature X-ray diffraction was used to measure the silicate's thermal expansion behaviour up to the point of crystallisation, where the mineral phase wollastonite was observed. Refined lattice parameters were in good agreement with standard values for wollastonite. The procedure as implemented does result in the formation of a small amount of poorly ordered carbonate, which can be removed by post-drying annealing. The carbonation in the presence of CO₂ of the dried amorphous silicate was also investigated, showing the conversion to CaCO₃ calcite and SiO₂.     

γ-ray irradiation induced multiple effects on Ge–As–Se chalcogenide glasses

In this work, multiple effects of γ-ray irradiation on properties of bulk Ge–As–Se chalcogenide glasses were studied. Increased density (ρ), thermal expansion coefficient (α) and decreased optical band gap (E_opt) were observed after irradiation, depending on glass compositions. Glasses with stoichiometric (GeSe₂)_100?x(As₂Se₃)_x compositions showed linear correlations between As₂Se₃ proportion x and irradiation sensitivity, which is expressed by Δρ/ρ, Δα/α and ΔE_opt/E_opt. Nonstoichiometric glasses (Ge₂Se₃)_100?x(As₂Se₃)_x exhibited irregular variations. The phenomena are discussed in terms of chemical bonds transition and structural evolution under γ-ray irradiation.     

Structural dependence of ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses

Ultrafast third-order optical nonlinearity of Ge–Ga–Ag–S chalcogenide glasses at the wavelength of 820 nm has been measured using femtosecond time-resolved optical Kerr (OKE) technique. The results show that Ge–Ga–Ag–S glasses have large third-order optical nonlinear susceptibility, χ⁽³⁾ and the response time is also subpicosecond, which are predominantly due to the ultrafast distortion of electron cloud surrounding the balanced positions of Ge, Ga, Ag and S atoms. What’s more, a strong dependence of χ⁽³⁾ on the composition and microstructure of these glasses was found which shows that [GeS₄] and [GaS₄] tetrahedra play an important role on the third-order optical nonlinearity. These Ge–Ga–Ag–S chalcogenide glasses would be expected as promising materials applied on all-optical switching devices.     

Kinetics of crystallization process of Mg–Cu–Gd based bulk metallic glasses

The crystallization behavior of Mg₆₁Cu₂₈Gd₁₁ and (Mg₆₁Cu₂₈Gd₁₁)₉₈Cd₂ bulk metallic glasses was studied using DSC in the mode of continuous and isothermal heating, and its crystallization process and microstructure were confirmed by XRD and TEM. In continuous heating, the activation energies of glass transition, onset and peak crystallization were determined by the Kissinger method, which yields 110 ± 12, 77 ± 9 and 79 ± 10 kJ/mol, respectively, for Mg₆₁Cu₂₈Gd₁₁ glassy alloy, and 144 ± 10, 126 ± 6 and 131 ± 5 kJ/mol, respectively, for (Mg₆₁Cu₂₈Gd₁₁)₉₈Cd₂ glassy alloy. The isothermal kinetics was modeled by the Johnson-Mehl-Avrami equation. The Avrami exponent of the base alloy was in the range from 1.98 to 2.56 (± 0.01), which indicated a decreasing nucleation rate and a diffusion-controlled growth. For Cd-added glassy alloy, the Avrami exponent was in the range from 3.26 to 4.08, which indicated an increasing nucleation rate. The activation energies in isothermal process were calculated to be 88 ± 2 and 132 ± 2 kJ/mol, respectively, for the base and Cd-added glassy alloys. It was found that Mg₂Cu phase was the primary phase in the initial crystallization and the strong affinity between Cd and Mg/Gd tended to impose resistance to the formation of Mg₂Cu phase and thus improves the thermal stability.