The structure and optical properties of GeO2-GeS2 glasses

Oxy-chalcogenide glasses with compositions of xGeO₂-(100 − x)GeS₂, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS₂ by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO₂-GeS₂ glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO₂. This dependence suggests that the optical gap is governed by GeS₂ clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures.     

The effect of composition on UV-vis-NIR spectra of iron doped glasses in the systems Na2O/MgO/SiO2 and Na2O/MgO/Al2O3/SiO2

Glasses with the compositions xNa₂O · 10MgO · (90 − x)SiO₂, 10Na₂O · xMgO · (90 − x)SiO₂, 5Na₂O · 15MgO · xAl₂O₃ · (80 − x)SiO₂, xNa₂O · 10MgO · 10Al₂O₃ · (80 − x)SiO₂, 10Na₂O · 10MgO · xAl₂O₃ · (80 − x)SiO₂, 10Na₂O · 5MgO · 10Al₂O₃ · (80 − x)SiO₂ were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm⁻¹. At [Al₂O₃] > [Na₂O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm⁻¹ attributed to Fe²⁺ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm⁻¹ increases. This is explained by the incorporation of iron in the respective glass structures.     

Doping-induced formation of bulk nanocrystalline alloy from metallic glass with controllable microstructure and properties

We report the formation of bulk nanocrystalline alloys from a Pr-based bulk metallic glass-forming alloy by doping iron. The microstructure of the alloys can be tuned progressively from full glassy state to composite with nanocrystalline particles in the glassy matrix, and finally into nanostructured state accompanying with the gradual magnetic and mechanical changes. The role of the addition in the control of microstructure and magnetic property, the mechanism for the nanocrystalline formation induced by addition, and the relation between the microstructure and properties are discussed.     

Distributions of copper and CuBr in CuBr nanocrystallite-dispersed glasses prepared by copper staining

CuBr nanocrystallite-dispersed glasses were prepared by incorporation of copper into bromide ion-containing borosilicate glass using the technique of copper staining. The copper ion incorporation process was mainly controlled by ionic diffusion from the surface to the interior of the glass. The depth profiles of Cu and CuBr concentration were examined by energy dispersive X-ray analysis and by reference to the change in absorption intensity assigned to the CuBr exciton band along the depth. While the Cu concentration was found to decrease monotonically, the CuBr concentration profile showed a maximum at a distance of 10-50 μm from the glass surface. Although the depth reached by the copper ions became greater with increasing heat-treatment time, the depth at which CuBr was precipitated was found to be saturated. This means that regions were found in the glasses in which no CuBr crystallites precipitated, although migration of Cu ions to these regions had taken place.     

Effect of ZnO and Bi2O3 addition on linear and non-linear optical properties of tellurite glasses

Glasses in the system TeO₂-Bi₂O₃-ZnO were studied with respect to their linear refractive indices and optical absorption in the UV-vis range. The third order non-linear refractive indices were measured using degenerated four wave mixing (DFWM). The optical Kerr susceptibilities calculated hereof were in the range from 5.49 to 6.58 × 10⁻¹³ esu and hence 34-41 times larger than that of fused SiO₂. They are roughly proportional to values theoretically calculated by the theory of Lines.     

Density-structure correlations in Na2O-CaO-P2O5-SiO2 bioactive glasses

Relations for Na₂O-CaO-SiO₂ glasses have been developed to calculate the density of Na₂O-CaO-P₂O₅-SiO₂ bioactive glasses. The calculation makes use of NMR results of O’Donnell et al. indicating that P₂O₅ forms a separate phase, containing Na₃PO₄ and Ca₃(PO₄)₂, in the investigated glasses. The volume of the silicate units is the same as that found in Na₂O-CaO-SiO₂, Na₂O-SiO₂, and CaO-SiO₂ glasses. Similarly, the volume of PO₄ units is equivalent to that in Na₃PO₄ and Ca₃(PO₄)₂. Calculated densities are consistent with the experimental data.     

Spectroscopic parameters related to non-bridging oxygen hole centers in amorphous-SiO2

The relationship between the luminescence at 1.9 eV and the absorption bands at 2.0 eV and at 4.8 eV were investigated in a wide variety of synthetic silica samples exposed to different γ- and β-ray irradiation doses. We found that the intensities of these optical bands are linearly correlated in agreement with a model in which they are assigned to a single defect. This finding allows the determination of spectroscopic parameters related to the optical transitions efficiencies. In this case the absorption oscillator strength at 4.8 eV is ∼200 times higher than that at 2.0 eV; while the 1.9 eV luminescence quantum yield under 4.8 eV excitation is lower (by a factor ∼3) than that under 2.0 eV excitation. These results are consistent with the energetic level scheme proposed in the literature for the non-bridging oxygen hole center. Moreover, they account for the excitation → luminescence pathways occurring after UV and visible absorption.     

The structure of SiO2-GeO2 glasses: A spectroscopic study

Four glasses of the SiO₂-GeO₂ binary system have been synthesized via a sol-gel route followed by a heat treatment and a quench. Glass structure has been determined by Ge K-edge X-ray absorption spectroscopy (XAS) at low temperature and Raman spectroscopy. These mixed glasses present a continuous random network of interconnected GeO₄ and SiO₄ tetrahedra, with GeO₄ tetrahedra similar to the GeO₄ units in GeO₂ glass and continuous compositional variations from GeO₂-rich regions to SiO₂-rich regions. Such a random mixture is consistent with physical properties of these binary glasses as well as with the chemical dependence of their polyamorphism at high pressure. This EXAFS-derived mean Ge-O-Si angles are close to the Ge-O-Ge mean angle in GeO₂ glass, 134° and 130°, respectively. This misfit with the Si-O-Si angles might explain the ease of formation of isolated and pair defects centers, which are suspected to be at the origin of photo-induced modifications of optical properties in Ge-bearing SiO₂ glasses.     

The study on the phosphate glass melted by microwave irradiation

In this study, NH₄H₂PO₄, Li₂CO₃, and Ca(OH)₂ raw materials were mixed with and without adding water or pressing pressure. The three types of mixture (i.e., raw mixtures, waterish mixtures, and dense mixtures) were then subjected to microwave irradiation. The samples were characterized by various methods of analysis method. With adding water, the particles changed from irregularity into aggregation. Simultaneously, the existence of H₃PO₄ and increase in hydroxyl group of waterish mixtures is due to the decomposition of NH₄H₂PO₄, which could promote microwave absorption. In addition, dense mixtures could change into glass after microwave irradiation with increasing pressing pressure. The connection between mixtures with and without adding water or pressing pressure and degree of microwave absorption, and how they are influenced on glass formation is discussed.     

Glass formation ability and mechanical properties of Ti40Cu40Zr10Ni10 alloy

Melt-spun ribbon and bulk samples in cylindrical rod form with diameter ranging from 2 mm to 4 mm of Ti₄₀Cu₄₀Zr₁₀Ni₁₀ alloy were prepared by melt-spinning technique and copper mould casting method, respectively. The microstructure, thermal stability and mechanical properties of the bulk samples were investigated. A completely glassy single phase is formed in the 2 mm rod sample. Increasing the diameter of the rod samples resulted in the formation of CuTi crystalline phase in the 3 mm and 4 mm rod samples. The 2 mm single glassy rod sample exhibited a large supercooled liquid region ΔT_x = 58 K and γ = T_x/(T_g + T_l) is 0.390, which indicated that the alloy possessed a good glass-forming ability. The bulk samples also exhibited good mechanical properties. The 2 mm rod sample showed the highest yield strength of about 2086 MPa. The 3 mm rod sample not only showed high yield strength of about 2000 MPa, but also enhanced plastic strain of about 0.71%.     

Icosahedral and dense random cluster packing in metallic glass structures

It has recently been shown that metallic glass structures can be idealized as inter-penetrating solute-centered atomic clusters that are packed with essentially periodic symmetry. The present work applies the same methodology to explore whether experimental observations can be matched by inter-connected solute-centered clusters that are organized in space via dense random cluster packing, Bergman icosahedral cluster packing or Mackay icosahedral cluster packing. Idealized partial pair distribution functions are developed where the symmetry of the solute positions in the structure is derived from the cluster-packing symmetry and the solute concentration, which establishes occupation of inter-cluster sites, especially β structural sites enclosed by an octahedron of solute-centered clusters. While each of the three models matches major features of the measured solute-solute partial pair distribution functions, the arrangement of clusters with Mackay icosahedral ordering provides the best fit. However, this model is not able to match an essential feature in solute-lean glasses and does not provide the same overall agreement as does periodic cluster packing for solute-rich glasses. Strong similarities between the structure factors in the Mackay icosahedral and periodic cluster-packing models, along with expected deviations from the idealized solute positions studied here, are likely to hinder an unambiguous distinction between these two models.     

Dense amorphous packing of binary hard sphere mixtures with chemical order: The stability of a solute ordered approximant

Recently, Miracle proposed that the intermediate structure in metallic glasses could be usefully characterized as an ordered face centered cubic packing of solute-centered coordination clusters. In this paper we examine the stability of such solute ordered arrangements in binary hard sphere mixtures subject to density maximization through local particle moves.     

Development and properties of a glass made from MSWI bottom ash

A uniform shiny black-coloured glass was obtained using bottom ash produced by a Portuguese municipal solid waste incinerator (MSWI). The bottom ash was the single batch material used in the formation of the glass, which was obtained by vitrification of the solid waste at 1400 °C for 2 h. Under these conditions, a homogeneous melt with an appropriate viscosity to be shaped was obtained, indicating the suitability of this waste material to be employed in the development of vitreous products. The characterization of the resulting glass was performed in order to assess its structural, physical, mechanical, thermal and chemical features. The glass had a density of 2.69 g cm⁻³, a hardness of 5.5 GPa, a fracture strength of 75 MPa, a thermal expansion coefficient of 9.5 × 10⁻⁶ °C⁻¹ and it exhibited a very good chemical stability. In summary, the MSWI bottom ash glass has good mechanical and chemical properties and may, therefore, be used in several applications, particularly as a construction material.     

Influence of TM and RE elements on glass formation of the ternary Al-TM-RE systems

The effects of TM and RE elements on glass formation ability (GFA) of the Al-TM-RE systems are studied systematically. The TM elements show distinct differences: critical sizes of the Al-TM-Ce systems are in the order of Ni > Co > Fe > Cu. However, the RE elements show similar effect on glass formation. These results are discussed in terms of the GFA-related factors, i.e., reduced glass transition temperature (T_rg = T_g (T_x)/T_L, where T_g, T_x and T_L are the glass transition temperature, onset crystallization temperature and liquidus temperature, respectively) and the mixing enthalpy ΔH_Al-TM. A new parameter of T_L − T_g (T_x) is potentially proposed and used to evaluate the GFA of the Al-based alloys, as well as bulk glass-formers.     

Influence of structural relaxation on atomic mobility in a Zr41.2Ti13.8Cu125Ni10.0Be22.5 (Vit1) bulk metallic glass

The effect of an annealing at a temperature above or below the glass transition temperature in a Zr_41.2Ti_13.8Cu₁₂₅Ni_10.0Be_22.5 bulk metallic glass was investigated using dynamic mechanical analysis. Structural relaxation influences both the storage modulus (elastic component) and the loss modulus (viscoelastic component). Kinetics can be captured by a stretched exponential relaxation function. Experimental results are correctly described using a physical model based on the concept of defects for the mechanical response of amorphous materials and especially for the characteristic time relative to atomic mobility.     

Packing as a probe of structure in alkaline earth glass systems

Packing is an intrinsic property of glass, defined as the ratio of ionic volume to molar volume, and is a useful parameter for analyzing structural changes with composition. Alkali based glasses show two trends in packing, one dominated by the oxygen covalent network for the small ions, Li and Na, and one ionically dominated by the metal cations for the large, K, Rb and Cs cases [S. Giri, C. Gaebler, J. Helmus, M. Affatigato, S.A. Feller, J. Non-Cryst. Solids 347 (2004) 87]. We have found that alkaline earth glasses do not display these behaviors, and in this paper we determined the packing fractions of these glasses and compared them with the alkali case. Further, we considered the structural implications of the packing trends.     

Theoretical prediction of bulk glass forming ability (BGFA) of Ti-Cu based multicomponent alloys

The bulk glass forming ability (BGFA) of Ti-Cu based multicomponent alloys has been evaluated via theoretical modeling and computer simulation studies based on a combination of electronic theory of alloys in the pseudopotential approximation and the statistical thermodynamical theory of liquid alloys. The magnitude of atomic ordering energies, calculated by means of the electronic theory of alloys in the pseudopotential approximation, was subsequently used for calculation of the key thermodynamic parameters such as enthalpy, entropy and Gibbs free energy of mixing, viscosity, and critical cooling rate of the binary Ti-Cu and ternary Ti-Cu-X alloys. The potential alloying elements (X) can be divided in two groups defined by their effect on the variation of the negative heat of mixing and their influence on the critical cooling rate. Most of the predicted candidate alloying elements from either X_I (Al, Si, Ag) or X_II (Co, Ni, Fe, Sn, Be) and/or both groups have already been used successfully for the fabrication of new Ti-Cu based bulk metallic glasses. It was also shown that the critical cooling rate appears to be a more important parameter rather than the change in the negative heat of mixing for the prediction of candidate alloying elements improving BGFA.     

Characterization of new sulfur and selenium-based glasses containing lead iodide

The aim of this work is to investigate and qualify vitreous regions in new chalcogenide systems containing highly polarizable elements like S, Se, As, Sb, Bi, Pb and I. The sulfur based system, As₂S₃-Sb₂S₃-Bi₂S₃-PbI₂, as well as the selenium containing glasses As₂Se₃-Sb₂Se₃-PbI₂ have been studied. Large vitreous regions have been defined in the both systems: sulfur and selenium. Indeed, several glass compositions can accept in the vitreous network a molar concentration near 50% of PbI₂. Physical properties such as glass transition temperature, crystallization temperature, optical transmission, band-gap wavelength have been measured versus glassy compositions.