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.     

Structure–property correlations in lead borate and borosilicate glasses doped with aluminum oxide

Glass samples from four systems: xPbO–(100?x)B₂O₃ (x = 30, 40, 50 and 60 mol%), 50PbO–yAl₂O₃–(50?y)B₂O₃ (y = 2, 4, 6, 8 mol%), 50PbO–ySiO₂–(50?y)B₂O₃ (y = 5, 10, 20, 30 mol%) and 50PbO–5SiO₂–yAl₂O₃–(45?y)B₂O₃ (y = 2, 4, 6, 8 mol%) were prepared by a melt-quench technique. Characterization of these systems was carried out using density measurements, UV–visible spectroscopy, differential scanning calorimetry (DSC), and ¹¹B and ²⁷Al magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). Our studies reveal an increase in glass density with increasing lead(II) oxide concentration in pure lead borates and also with addition of silica into 50PbO–50B₂O₃ glass. ¹¹B MAS NMR measurements determine that the fraction of tetrahedral borons (N₄) reaches a maximum for the glass containing 50 mol% of PbO in the PbO–B₂O₃ glass series and that N₄ is sharply reduced upon adding small amounts of Al₂O₃ into lead borate and lead borosilicate systems. ²⁷Al MAS NMR experiments performed on glasses doped with aluminum oxide show that the Al³⁺ are tetra-, penta- and hexa-coordinated with oxygen, even without any excess concentration of Al³⁺ over charge-balancing Pb²⁺ cations. ^[5]Al and ^[6]Al concentrations are found to have unusually high values of up to 30%. The results of UV–visible absorption spectroscopy, DSC and density measurements support the conclusions drawn from the NMR studies, providing a consistent picture of structure–property relations in these glass systems.     

Composition analysis of glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

Composition change during the melting process of some glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system melted at 450–470°C for 15 min was studied. Results show that there was a remarkable difference between the batch composition and the analyzed composition. Large amount of P, Br, Pb, and Cl were lost mainly in the form of PbBr₂, PbCl₂ and P₂O₅. The content of O is influenced by two factors. The incomplete decomposition of NH₄H₂PO₄ or the reaction between P₂O₅ and H₂O in the atmosphere increases the content of O, while the volatilization of P₂O₅ decreases the content of O.     

Atomic structure and chemical order in binary Ge–Te and As–Te glasses: A Te K-edge X-ray absorption fine structure spectroscopic study

The nearest-neighbor coordination environments of Te atoms in Ge_xTe_100?x glasses with x = 15 and 20 and in As_xTe_100?x glasses with 40 ? x ? 65 have been studied with Te K-edge EXAFS spectroscopy. The average coordination number of Te atoms in all glasses is found to be ～2.0 and no violation of the 8-N rule is observed. The compositional makeup of the first coordination shell of Te atoms indicates that chemical order is largely preserved in both glass-forming binary systems. Sudden changes in the Te coordination environment and violation of chemical order are observed at the stoichiometric As₄₀Te₆₀ glass implying formation of a constrained network. The compositional dependence of the physical properties in both systems can be correlated to short-range chemical order.     

X-ray absorption near edge structure investigation of iron–sodium silicate glasses

X-ray absorption near edge structure spectroscopy has been used at the O K and Fe L_2,3 edges to investigate the electronic and atomic structure of (Fe₂O₃)_x(Na₂O)_0.30(SiO₂)_0.70 ? x (x < 0.2) obtained by melt-quench technique. The Fe L_2,3 edge spectra show that the Fe atoms are in octahedral coordination. The O K edge spectra reveal no change in coordination of Fe and increased degree of hybridization between O 2p and Fe 3d orbitals with iron doping. It is estimated that about 10% Fe²⁺ and 90% Fe³⁺ are in these glasses by peak fitting analysis of Fe L₃ edge. The ligand-field splitting of Fe 3d orbital is about 1.6 eV.     

FTIR and UV–VIS spectroscopy investigations on the structure of the europium–lead–tellurate glasses

Glasses in the xEu₂O₃·(100-x)[4TeO₂·PbO₂] system where 0 ≤ x ≤ 50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO₃] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu^+ 3 content causes the intercalation of [EuO_n] entities in the [TeO₄] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbO_n] and [EuO_n] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu²⁺ and Eu³⁺ valence states, the last being predominant in the studied glasses. The Pb^+ 2 ions produce strong absorption in the ultraviolet domain.     

Optical spectroscopy and local structure of Er3+ luminescence centres in СaO–Ga2O3–GeO2 glasses

Optical absorption, luminescence excitation and emission spectra of Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass with Er content of 1.46 wt% are presented and analysed. Luminescence kinetics for the main Er³⁺ transitions was satisfactorily described by single exponential decays with characteristic lifetimes. Oscillator strengths, phenomenological Judd–Ofelt intensity parameters, radiative decay rates (emission probabilities of transitions), branching ratios and radiative lifetimes for Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂:Er glass are calculated and compared with the corresponding parameters of the Ca₃Sc₂Ge₃O₁₂:Er³⁺ garnet and other crystals and glasses. Quantum efficiency, η, of the ⁴I_13/2 → ⁴I_15/2 Er³⁺ transition is determined. Incorporation peculiarities and local structure of Er³⁺ luminescence centres in Ca₃Ga₂Ge₃O₁₂:Er³⁺ glass are discussed in comparison with garnet crystals and oxide glasses. On the basis of the presented results and referenced EXAFS data for Er, Eu and Ho impurities (L₃-edge) it has been shown that Er³⁺ centres in Ca₃Ga₂Ge₃O₁₂ glass occupy network sites with the coordination number to oxygen of N = 6.     

Synthesis,structure and fluorescent property of a novel inorganic–organic zinc compound

Single crystals of a symmetrically substituted molecule, [Zn(C₃N₆H₆)(H₂O)_0.5Cl₂] (C₃N₆H₆)(H₂O)(1), have been obtained. The crystal structure of 1 shows the existence of novel layered type supramolecular structure constructed by dumbbell-shape coordinated Zn moleculeand one 2,4,6-triamine-s-triazine ligand. Crystallographic data for 1: monoclinic system, space group: C2/c, a = 12.2532(9), b = 13.8606(10), c = 18.3603(13) Å, = 99.7860(10), V = 3072.9(4) ų and Z = 8, D_c = 1.758 Mg/m³, R₁ = 0.0518. The fluorescent property of 1 has also been studied. The luminescent property of 1 attributable to both ligand ^* transitions and electronic transfer of Zn^II O transitions.     

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.     

Spectroscopic studies of tungsten ions in PbO–PbF2–SiO2 glasses

40PbO–(10 ? x)PbF₂–50 SiO₂:xWO₃ (where x = 1 to 7 mol%) glasses are prepared in the glass forming region. Spectroscopic studies (UV–Vis absorption, ESR, IR) are carried out for these glasses. Interesting changes are observed in the spectroscopic parameters of these glasses when the concentration of WO₃ is changing in the glass matrix. Two absorption bands are observed around at 830 and 620 nm. ESR signal are measured at room temperature for these glasses, the strength of the signal is increased and hyperfine splitting is resolved with increasing the concentration of WO₃ in the glass matrix. IR transmission gives valuable information about the nature of bonds in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

Ion conductive chalcohalide glasses in LiI–Ga2S3–GeS2 system

The electric properties of LiI containing chalcohalide glasses in the system Ga₂S₃–GeS₂ were studied by means of impedance spectroscopy and potentiostatic chronoamperometry. Two sets of the samples were prepared by direct synthesis from elements and compounds in evacuated quartz ampoules. The prepared glasses were as follows: xLiI–xGa₂S₃–(100?2x)GeS₂, x = 15, 20, 25 and 20LiI–xGa₂S₃–(80?x)GeS₂, x = 0, 5, 10, 15 and 20. In the first set the concentration of LiI increased and the second set was prepared to study the influence of Ga₂S₃ on the properties of the glasses. Additional aim of this work was to compare the electric properties of LiI containing Ga₂S₃–GeS₂ glasses with analogous AgI containing Ga₂S₃–GeS₂ glasses recently studied by us. The conductivity of the LiI containing glasses in the Ga₂S₃–GeS₂ system was higher and the activation energy was lower than in the analogous AgI containing system. The residual electronic (hole) conductivity remained similar in both systems being almost negligibly low. Raman spectroscopy proved the influence of LiI as well as Ga₂S₃ on glass structure, however interpretation of Raman spectra of these glasses is complicated due to small mass difference between gallium and germanium.     

Bi precipitates in Na2O–B2O3 glasses

Bi particles of different sizes were produced in Na₂O–B₂O₃ glasses by melt quenching and heat treatment technique. Melting temperature of Bi particles was measured by differential scanning calorimetry and X-ray diffraction. Measured melting temperatures of Bi particles are lower than bulk Bi melting temperature. Results of transmission electron microscopy were analyzed for the dependence of melting temperature on particle radius. The pressure and surface energy effect on melting temperature is estimated. The melting behavior of Bi particles in Na₂O–B₂O₃ glasses depends on the difference in the interfacial energies between the solid particle/glass and liquid particle/glass, and liquid particle/glass, σ_sm−σ_lm, which is estimated to be 255×10⁻³ J m⁻².     

Further Meyer–Neldel rule in thermally activated crystallization of chalcogenide glasses

This paper reports the observation of the Further Meyer–Neldel rule in thermally activated crystallization in Se_80?xTe₂₀M_x (M = Ag, Cd, In and Sb); 0 ? x ? 15 chalcogenide glasses. We have investigated Further Meyer–Neldel rule by two different approaches. In the first case, the different sets of Meyer–Neldel pre-factor K₀₀ and Meyer–Neldel energy E_MN are obtained by changing the composition (i.e., value of x) of a particular glassy system keeping the third element (i.e., value of M) constant. In the second case, the different sets of Meyer–Neldel pre-factor K₀₀ and Meyer–Neldel rule energy E_MN are obtained by changing the third element in a particular glassy system keeping the composition constant. The results are explained using the conception of thermal phonons in thermally activated crystallization analogous to optical phonons in thermally activated electric conduction.     

Spectroscopic properties and ab initio calculations on the structure of erbium–zinc-borate glasses and glass ceramics

Glasses in the (Er₂O₃)_x·(B₂O₃)_(60 ? x)·(ZnO)₄₀ system (0 ≤ x ≤ 15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er₂O₃ content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp² planar [BO₃] units to the more stable sp³ [BO₄] tetrahedral structural units. The linkages of the [BO₄] structural units can polymerize in [B₃O₉]^? 9 cyclic trimeric ions which will produce the ErBO₃ crystalline phase. An increase of the efficiency corresponding to the ⁴I_15/2 state to ⁴I_11/2 state (4f–4f) transitions of Er^+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO₄], [ZnO₄] and [Zn₄O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.     

X-ray diffraction analysis on the structure of the glasses in the system PbOSiO2

The structures of PbO·SiO₂ and 2PbO·SiO₂ glasses have been analyzed by use of X-ray diffraction data and pair function method. For PbO·SiO₂ glass, a model consisting of chains of PbO₃ pyramids and silicate chains showed good agreement with the observed RDF. For 2PbO·SiO₂ glass, the present authors reported previously a model in which chains of PbO₃ pyramids are connected with SiO₄ tetrahedra, while the chromatographic analyses of silicate anions by Götz et al. and Smart et al. showed that silicate anions are distributed from monomer to polymer in the glass. We reexamined the structure of this glass referring to these results. Three representative models containing isolated SiO₄, Si₄O₁₂ rings and (SiO₃)_n chains respectively as well as PbO₃ chains were constructed and the RDFs were calculated with changing structure parameters. These three models showed satisfactory agreement with the observed data, showing that silicate anions are distributed from monomer to polymer in 2PbO·SiO₂ glass and an increase of SiO₂ content leads to polymerization of silicate anions to longer chains up to PbO·SiO₂ composition, while the chains of PbO₃ pyramids remain unchanged.     

On the origin of the high Kerr coefficient measured in thallium–zinc–tellurite glasses

Measurements of Kerr electrooptical sensitivity of several zinc–thallium–tellurite glasses are presented, and composition dependence of Kerr sensitivity is compared with the dependence of the second harmonic generation efficiency collected for optically poled TeO₂–TlO_0.5–ZnO glasses. These data being analyzed jointly with Raman measurements data allowed us to conclude that the high electrooptical Kerr coefficient and nonlinearity of Tl₂O–ZnO–TeO₂ glasses, and their sharp increase with augmenting concentration of thallium oxide TlO_0.5 above 15% should be attributed to the presence of Tl⁺ cations having very high non-linear polarizability most likely related to their electronic lone pairs.     

Evaluating Mohr–Coulomb yield criterion for plastic flow in model metallic glasses

The yielding of metallic glasses (MGs) is generally considered to be dependent on pressure or normal stress, which is usually described by the Mohr–Coulomb yield criterion. Experimentally, the orientation of the shear band angle or fracture angles in MG is roughly 40° to 42° in uniaxial compression and 50° to 59° in uniaxial tension, both with respect to the loading direction. However, the amounts of deviation from the maximum shear stress direction (45°) under uniaxial tension and compression are quite different, which seems to be inconsistent with the Mohr–Coulomb yield criterion. Here we carried out molecular dynamics simulations to study the incipient plasticity of model Dzugutov glasses subjected to various uniaxial and biaxial stress states. The yield points are defined as the sharp rise of the population of atoms participating in non-affine deformations, in addition to the traditional offset method. The yield surfaces thus created agree well with the Mohr–Coulomb yield criterion. Furthermore, the orientations of the embryonic shear bands (instead of the fully-grown shear bands, or fracture planes) are measured, which also follow predictions based on the Mohr–Coulomb criterion. Our simulation results call for orientational measurement of incipient shear bands in experiments to critically examine the Mohr–Coulomb yield criterion in MG systems.     

Thermal properties of chalcogenide glasses in the GeSe2–As2Se3–CdSe system

In the present work, thermal properties of GeSe₂–As₂Se₃–CdSe glasses were investigated via DSC measurements. The dependences of glass transition temperature and thermal stability on glass composition were discussed. XRD measurement was also performed to validate the effect of cadmium on the thermal properties of glasses. The calculated Avrami exponent was used to demonstrate the three-dimensional growth of crystals in the glass matrices. The crystallization kinetics for the glasses was studied by using the modified Kissinger and Ozawa equations.     

Ultrasonic wave velocities and attenuation in IVb-Vb-VIb chalcogenide glasses: 2–300 K

The velocities and attenuation of longitudinal and shear ultrasonic (12 MHz) waves have been measured for several chalcogenide glasses (Ge₁₀Si₁₂As₃₀Te₄₈, Ge₂₀As₃₀Se₅₀, Si₂₀As₃₂Te₄₈, Ge₁₀Si₁₂As₂₉Te₄₉, Ge₁₂S₁₄As₃₅Te₄₉). The bulk, shear and Young's moduli and the Poisson ratio are found to be insensitive to the glass composition. The temperature dependences of the longitudinal and shear-wave velocities are negative at higher temperatures and approach 0 K with a zero slope. The ultrasonic attenuation does not exhibit either the broad loss peak or the smaller low-temperature peak found in many other glasses: the elastic and anelastic behaviour is quite different from that of oxide glasses — no evidence for the existence of two-level systems has been obtained from the ultrasonic measurements.