Photoinduced fluidity in chalcogenide glasses

Chalcogenide glasses such as As₂S₃ show prominent fluidity under intense subgap illumination. The feature is summarized, and the mechanism is discussed.     

The thermal stability of chalcogenide glasses

Crystallization processes of Ge_xS_1-x (0.322≤x≤0.44) glasses have been studied by thermal analysis and a new simple method of kinetic analysis is proposed. This method allows the definition of an appropriate model characterizing the crystallization process of glass, as well as calculation of reliable kinetic parameters. Results of kinetic analysis allow definition of a thermal stability criterion which has a general applicability for any glass-forming system. ICTA Young Scientist Award presentation     

NQR study of chalcogenide glasses Ge-As-Se

A three‐component Ge‐As‐Se system is studied by the nuclear quadrupole resonance (NQR) method on ⁷⁵As nuclei and by the nutation NQR spectroscopy. The NQR ⁷⁵As spectra of the glasses Ge_0.021As_0.375Se_0.604, Ge_0.043As_0.348Se_0.609 and Ge_0.068As_0.318Se_0.614reveal broad lines with two peaks assigned to the main structural unit of As₂Se₃. With increasing average coordination number (r?), the spectrum signals are shifted towards higher frequencies. At r? > 2.54, the spectrum becomes complex, which is a consequence of formation of more complex molecular structures in the glasses of high content of germanium. At fixed frequencies the asymmetry parameter η of the samples studied is determined. Copyright © 2011 John Wiley & Sons, Ltd.     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Temperature dependence of the thermophysical properties of polycrystallene chalcogenide glasses

The specific heat (C _p), thermal conductivity (λ), thermal diffusivity (a), and electrical conductivity (σ) were measured for polycrystalline HgS and Sb₂S₃ in the temperature range 300–600 K. The measurements were performed with an experimental apparatus based on a socalled flash method. The results showed that the mechanism of heat transfer is mainly due to phonons, whereas the contribution of electrons and bipolars is very small indeed. The energy gap of the samples was also calculated.     

Calorimetric measurement of structural relaxation in chalcogenide and metallic glasses

Some special characteristics of the structural relaxation (SR) in chalcogenide and metallic glasses are presented and the current theories dealing with the physical nature of the SR are recalled. The type of experiments used to measure SR by differential scanning calorimetry are reviewed and some rules to be taken into account when measuring calorimetrically the SR are stressed.

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Zusammenfassung Es werden einige spezielle Charakteristiken der Strukturrelaxation (SR) von Chalkogeniden und Metallgläsern vorgestellt und die gegenwärtigen Theorien über die physikalische Natur der SR zitiert. Die Art von Experimenten zur Messung von SR mittels DSC wurden kritisch besprochen und einige inbetrachtzuziehende Regeln für die kalorimetrische Bestimmung der SR hervorgehoben.

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This work was supported by the Comisión Interministerial de Ciencia y Tecnología (CICYT) project MAT88-0439.     

119Sn electric field gradients in model clusters of chalcogenide glasses

Calculations of ¹¹⁹Sn electric field gradients (EFG) have been performed using the Extended Hückel approximation on characteristic molecular clusters simulating possible types of sites in chalcogenide glasses. The motivation for these calculations derives from theoretical concepts on varying near neighbor relationships in these types of glasses, and from recent ¹¹⁹Sn Mössbauer experiments on Sn-doped Ge_x(Se or S)_1–x bulk glasses which reveal three types (A, B and C) of chemically inequivalent sites, with distinct values and composition dependences for their isomer shifts and quadrupole splittings. The model clusters chosen for the calculations were the ethane-like (Ge₂Se₃)_n quasi-one-dimensional chains of varying lengths which have been proposed as possible sources of the B site. In addition, calculations were also carried out on several additional types of clusters, in order to help in interpreting the results for the chains. We find that the magnitude of the quadrupole splitting in isolated linear ethane-like chains is very small, and almost independent of the particular site along the chain at which Sn replaces Ge. It therefore seems unlikely that such isolated linear clusters would be the source of the B sites. These sites are more likely to be related to distortions of the ethane-like clusters into non-linear configurations, as well as interactions with neighboring clusters, as forced by the constraints of the packing in the structure of the glass.     

Compositional dependence of the nonlinear refractive index of new germanium-based chalcogenide glasses

In this paper, we report results of n₂ measurements of new chalcogenide glasses in the Ge-Sb-S-Se system using a modified Z-Scan technique. Measurements were made with picosecond pulses emitted by a 10 Hz Q-switched mode-locked Nd-YAG laser at 1064 nm under conditions suitable to characterize ultrafast nonlinearities. The nonlinear index increases up to 500 times the n₂ of fused silica with an increase in the Ge/Se ratio and a decrease with an increase of the Ge/Sb ratio. We confirmed, using Raman spectroscopy, that the nonlinear refractive index depends on the number of Ge-S(Se) and Sb-S(Se) bonds in the glass network. Sulfide glasses were shown to have a nonlinear FOM near or <1, at 1064 nm.     

Thermodynamic consistency of data banks

Data sets originated from different sources are typically used simultaneously either in data banks or in data bases of flowsheeting programs. If these data sets concern different kinds of data, they ought to be in accordance with the laws of thermodynamics. This is not assured, however, and in many cases it is not even checked. Methods used for data compilation rely on approximate models, which may bias the residuals.

Two model-free methods are proposed, where the residuals of the thermodynamic differential equations are investigated.

The first method is a χ² test based on a quadratic form of the f residuals, involving variances of the elementary measurements, if they are available.

The second method is a rather sensitive trend/shift analysis of residuals, which does not require the knowledge of error variances.

The examples are the Clausius-Clapeyron equation, a binary vapor-liquid equilibrium data set and a simultaneous treatment of PVT and caloric data.     

Charged particle activation analysis of oxygen in fluoride and chalcogenide glasses used for fiber amplifiers

The proton activation analysis of oxygen was studied in fluoride and chalcogenide glasses used for fiber amplifiers. First, we studied the interfering nuclear reactions from glass matrices to determine the oxygen concentration in these glasses. By using substoichiometric separation for ¹⁸F after irradiation, we found that the oxygen concentration was 12 to 204 ppm in InF₃-based fluoride glass and 0.04% to 0.7% in chalcogenide glass containing sodium. We also discuss the relation between oxygen concentration and optical properties such as the infrared absorption spectrum and fluorescence lifetime.     

Thermodynamic data of the NZP compounds family

Summary The thermodynamic data for NZP compounds MZr₂(PO₄)₃ (M=Na, K, Rb, Cs, Zr_0.25) and Na₅D(PO₄)₃ (D=Ti, Zr) are reported. The heat capacities of the phosphates were measured between T=7 and T=640 K. The standard enthalpies entropies, and Gibbs functions of formation at T=298.15 K were derived. The obtained thermodynamic characteristics of phosphates of the NZP type structure and literature data are summarized. Thermodynamic functions of reactions of solid-state synthesis were calculated and the usability of ceramic technology for obtaining NZP compounds was proved.     

Thermodynamic properties of silicate glasses and melts: II. System SrO-SiO2

High-temperature mass spectrometry was used to determine the Gibbs energies, activities, and chemical potentials of SrO and SiO₂ in glasses and melts of the SrO-SiO₂ system in the temperature range 1840–1970 K. Negative deviations from the ideal behavior were revealed in the system. The standard enthalpies of formation and atomization of gaseous SrSiO₂ and SrSiO₃ were determined.     

Thermodynamic modeling of redox equilibria in sodium silicate glasses with low iron content

The available literature data on the content of oxidized and reduced iron forms in molten sodium silicates at temperatures the 1573?C1873 K and partial oxygen pressures 10^?8?0.21 bar have been scrutinized. On the basis of this information, the temperature dependence of the Fe₂O₃ activity coefficient in glass melts containing up to 4 mol % Fe (??Henrian?? solution) has been suggested in the framework of the quasi-chemical model. The results are compared with previous data.     

Thermodynamic properties of silicate glasses and melts: I. System BaO-SiO2

Gibbs energies, activities, and chemical potentials of BaO and SiO₂ in melts of the BaO-SiO₂ system within the temperature range 1840–1970 K were determined. A significant negative deviation from the ideal behavior was found in the system studied.     

The structure of ionically conductive chalcogenide glasses: a combined NMR,XPS and ab initio calculation study

This paper reports on the structural investigation of lithium and sodium thiosilicate crystals and glasses by means of X-ray photoelectron spectroscopy and ab initio calculation. The results are analysed in conjunction with previously reported ²⁹Si NMR data. While NMR proved to be an effective tool for the quantitative discrimination of edge- and corner-sharing tetrahedra existing in these materials, X-ray photoelectron spectroscopy (XPS) gives information on the nature of SiS bonds, i.e. bridging and non-bridging bonds. The main result is the noticeable difference existing between the structures of lithium and sodium thiosilicate glasses, which, according to XPS data, is due to different electronic redistributions over the network when one or the other alkali is added, the sodium addition resulting in a change in the electronic distribution over the entire network.     

Study of the EFG tensor at 75As nuclei in Ge‐As‐Se chalcogenide glasses

Asymmetry parameters of the electric field gradient tensor at ⁷⁵As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge‐As‐Se system by comparing the experimental and simulated ⁷⁵As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at = 2.425. Electron paramagnetic resonance spectra of the Ge‐As‐Se system were obtained for the first time. A comparison was made between the results of analysis of the Ge‐As‐Se system by nuclear quadrupole resonance and electron paramagnetic resonance methods, and this allowed us to make the supposition that a structural phase transition occurs at = 2.4 from two‐dimensional to three‐dimensional CGS structure. Copyright © 2013 John Wiley & Sons, Ltd.