Diffuse scattering and chemical short range order in binary metallic glasses

X-ray and neutron scattering from binary metallic glasses is discussed in the context of the Bhatia-Thornton equations for the structure factor. For neutrons a generalised form of the Bhatia-Thornton equation must be used when there are different isotopes present. By making a distinction between correlated and uncorrelated scattering centres an expression can be derived which shows clearly the different contributions to the total scattered intensity. Information about the relative visibility of the alloy components can be obtained from this expression and a figure of merit or degree of contrast between the species defined, which is helpful in understanding results of experiments performed to date.     

Inelastic neutron scattering studies of amorphous network solids

The inelastic neutron scattering technique provides information on the vibrational spectra of amorphous network glasses which extends that available from optical and resonance spectroscopy. A range of instrumentation is available to cover energies corresponding to relaxation phenomena (< 1 μeV) up to hydrogen stretching frequencies (500 meV). The resolution attainable is now sufficient to give data, the line width of which is dominated by the natural broadening caused by the structural variations in the networks. Additional information on atomic motions within a vibrational mode is given by the dependence of the scattered intensity on the magnitude of the scattering vector, Q, as revealed by the dynamical structure factor, S(Q, E). Low energy excitations (<10 meV) characteristic of the amorphous state have been related to anomalous low temperature thermal properties and also contain information on the range of topological order within the network. Experimental investigations using a variety of neutron inelastic scattering instrumentation to study vitreous silica, vitreous opal, vitreous boron trioxide, the amorphous germanium-selenium system and amorphous silicon containing hydrogen or deuterium are described. The results are used to discuss the possibilities and limitations of the method for testing structural models of network glasses.     

Raman scattering and nonlinear refractive index measurements of optical glasses

The absolute Stokes-Raman scattering cross section is measured for optical glasses of varying composition, from which the nuclear contribution to the nonlinear polarizability is determined. The nonlinearities increase progressively from fluoroberyllate compositions to fluorophosphate to phosphate to silicate and finally to heavy-metal oxide glasses. Although values of the total nonlinear polarizability vary by nearly two orders-of-magnitude it is determined that the ratio of the nuclear to the electronic contribution is nearly constant and is independent of the glass composition. The electrostrictive contribution to the nonlinear polarizability is also calculated using previously measured elasto-optic constants. Correlations in the atomic structure were determined by measuring the position of the lowest-frequency Raman scattering peak and it is found that the correlation length for pure one-component glasses is larger than multi-component glasses. Examination of the low-frequency scattering region shows that there is an 0xcess light-scattering below 30 cm^?1 in all glasses tested. This excess scattering in LaSF-7 was fitted between 2 to 20 cm^?1 to a Lorentzian centered at zero frequency with a halfwidth of 2.5 ± 1 cm^?1, while the fit in pure silica between 5 and 30 cm^?1 yields a halfwidth of 8 ± 3 cm^?1.     

Medium range order and optical properties of As2S3 glass

Low frequency Raman scattering and optical absorption edge were measured for As₂S₃ glasses quenched at temperature in the supercooling region of the glasses. It was found that both the Raman spectrum and the optical absorption edge shift to the lower energy side with the rise of the quenching temperature. The effects were interpreted in terms of the order of the arrangements of the layer-like clusters, which become more random as the quenching temperature goes higher.     

Non-equilibrium fluctuations as a plausible reason of the light scattered intensity peak in the glass transition region

The dependence of the scattered intensity on the time after a temperature jump in the glass transition region of oxide glasses was discussed. It was shown that this dependence had a maximum. It was found that the peak height and its location on the time scale depended on the prehistory of the glass. It was supposed that the reason for the enhancement of scattered intensity was the temperature gradient, which arose across the sample after the temperature jump. As the result of experimental studies it was shown that the peak height was proportional to the square of the temperature gradient. Taking into account these features it is assumed that the appearance of the maximum is associated with the non-equilibrium fluctuations produced by coupling between the hydrodynamic modes.     

Computed optical transmission records: An effect of dense-medium phase function as an approximate description of multiple light scattering

The optical properties of glassy slab may quickly evolve during crystallization processes. Especially, the optical transmission (OT) may change as a function of size, number density and refractive index of scattering domains (crystals). In later crystallization phases, the separation length of individual domains may be lowered significantly. This usually results in enhanced multiple scattering effects. Under elevated packing density conditions, the individual crystals can no more be treated as independent scatters. In principle, the scattered signals originated from two neighboring particles may interfere either constructively or destructively, thus implying variable intensity of light beams. As a consequence, the OT may oscillate when crystal sizes increase. Since these optical features completely differ from those known for single scattering approach, we analyze them in detail in this paper.     

Surface Plasmon Enhanced Vibrational Spectra of Monolayer Assemblies on Gratings and Rough Metal Surfaces

The vibrational spectra of monolayer assemblies of cadmium arachidate on smooth and rough silver substrates were obtained by surface infrared and surface plasmon enhanced Raman spectroscopy. The assemblies were laid down by the Langmuir-Blodgett deposition technique. For Raman scattering the intensity of the incident light was enhanced by grating coupling to surface plasmon optical modes of the metal or to localized plasmon modes in the case of rough surfaces. It was found that the different vibrational frequency regions corresponding, for example, to C-C and C-H stretching modes, were enhanced by selecting different scattering angles for collecting the inelastically scattered light. The Raman spectra of monolayer assemblies in contact with silver islands showed evidence of conformational disorder, i.e., the alkyl chains of some molecules were not in the all-trans configuration. In contrast, the infrared spectra did not show evidence of similar disorder. These observations were explained by assuming that the infrared photons sensed the majority undistorted molecular species, while the Raman photons came from a distorted minority species located in regions where optical electromagnetic fields were enhanced by shape plasmon resonances of the rough silver surface.     

Density fluctuations in silicate glasses

The potential use of inorganic glasses as waveguides at optical wavelengths has precipitated the need to understand the relationship between intrinsic optical loss and glass composition. The contribution to optical loss due to scattering from density fluctuations, is analyzed and discussed for various homogeneous (non-phase-separated) silicate glasses. The results show that binary alkali silicates in certain composition ranges form homogeneous glasses with density fluctuations less intense than that of pure silica glass. As third components added to these binary compositions alkali oxides (different from the one already present in the base glass), alkaline earth oxide (CaO) and Al₂O₃ cause further reductions in the magnitude of the density fluctuations.     

Slow dynamics of liquid Se studied by Infrared Photon Correlation Spectroscopy

We report on the study of the slow dynamics of supercooled and molten Selenium by means of dynamic light scattering. To achieve this in the present case, where the opaqueness of Se prevents visible light scattering measurements, we have developed a novel experimental setup using infrared radiation as the light source. By measuring the scattered intensity autocorrelation function we have been able to extract the average size of the Se clusters in the liquid state and determine the temperature dependence of the related diffusion coefficient which was found to exhibit Arrhenius behavior.     

A reversible optical transition in Se---Ge and P---Se---Ge glasses

A reversible optical transition has been found in thin films of Se---Ge and P---Se---Ge glasses. This optical transition is similar to that found in As---Se---Ge and As---Se---S---Ge glass films; heating causes the shift of the absorption edge to shorter wavelengths, and illumination moves it to longer wavelengths without crystallization. It was found that the presence of arsenic is not always necessary. Fundamental optical properties of these glasses, i.e. absorption constant, optical energy gap, change of the optical energy gap, and the refractive index by heating and illumination are reported. Change of the optical energy gap and the refractive index is small in Se---Ge and P---Se---Ge glasses, compared with that in As---Se---Ge and As---Se---S---Ge glasses.     

F-19 NMR study of the ordering of high field strength cations at fluoride sites in silicate and aluminosilicate glasses

Several glasses were synthesized to explore cation ordering at fluorine sites in silicate and aluminosilicate glasses. Utilizing ¹⁹F NMR, we found a significant (at least ∼30% of the total intensity) amount of the fluorine signal to be due to F-Mg(n) (fluorine with an unknown number of exclusively Mg²⁺ nearest neighbors) bonding in the Mg-aluminosilicates. By combining this with previous data on Ca- and Ba-aluminosilicate glasses, we demonstrated a clear trend of an increasing amount of F-M(n) type bonding with increasing field strength of the network modifying cation. This indicates that the higher field strength cations can more effectively compete with Al³⁺ for fluorine bonds. The mixed-modifier (Na,La)-silicate glasses have primarily F-M(n) type bonding, with a pronounced preference for bonding to the higher field strength La³⁺ over Na⁺. In addition, Si-F bonding was found in the (Na,La)-silicate glasses at a level (∼2% of the total intensity) comparable to that found in other silicate glasses, suggesting that Si-F bonding is consistently present in silicate glasses. The (Na,La)-silicate glasses also had unusually short spin-spin relaxation times, suggesting short (similar to crystalline fluorides) fluorine-fluorine distances in environments associated with La³⁺.     

Effect of optical basicity on Er3+ up-conversion luminescence in GeO2–R2O glasses

The effect of optical basicity on Er³⁺ up-conversion luminescence in germanate glasses is investigated under 980 nm excitation. The intensity of green and red up-conversion luminescence decreased with the increase in radius of alkali ion or Li₂O content, implying that up-conversion luminescence strongly relates to the optical basicity of glass host. On the other hand, as increasing the optical basicity, the red emission intensity decreased significantly, while the green emission intensity decreased slightly. It has been proposed that the up-conversion luminescence intensity was dominated by the optical basicity, which theoretically estimated from glass composition. The interaction mechanism between up-conversion process and optical basicity was proposed.     

Electric Critical Point in Barium Titanate Single Crystals

The present paper considers the results of an experimental investigation of the volume jump Δ V and the light scattering by Barium Titanate single crystal as a function of the external electric field E and the temperature T in a narrow region of the tetragonal-cubic phase transition. It has first been established through X-ray and optical investigations that the same characteristic phenomena accompany the critical point for BaTi0₃, using an applied electric field in the capacity generalized force, and the critical point of other systems, i.e. a monotonous decrease in the volume jump between the two crystaline phases and an abrupt increase in the intensity of the scattered light.     

Remark on the optical gap in ZnO-Bi2O3-TeO2 glasses

Four ZnO-Bi₂O₃-TeO₂ glasses were prepared from high purity (4N5) oxides. From measurements of the optical transmission on very thin bulk samples the optical gap was determined at around 3.55 eV for the glasses studied. The temperature dependence of the optical gap was also determined from the room temperature close up to 500 K. Preliminary Raman scattering measurements indicate that with a decrease in TeO₂ content, TeO₄ trigonal bipyramid transformation proceeds into TeO₃ trigonal pyramids.     

The Rayleigh scattering loss in silicate glasses containing PbO

The Rayleigh scattering coefficients of a number of glasses in the K₂OMgOPbOSiO₂ system have been determined. The scattering by density fluctuations and by concentration fluctuations was calculated using theories which were developed for ideal multicomponent liquids. In order to investigate how these theories could be applied to multicomponent glasses, the scattering by concentration fluctuations was calculated making different assumptions. It was found that reasonable agreement, both in trends and in order of magnitude, was obtained between the calculated and observed scattering coefficients when the glass was considered to be a frozen-in mixture of silicate units with compositions corresponding to those of crystalline silicates.     

Optical properties of Nd3+ in lead phosphate glasses

Measurements of optical absorption and emission spectra of Nd³⁺ in lead phosphate glasses at 295 K are compared with results reported earlier for various metaphosphate glasses. The Judd-Ofelt intensity parameters for high-lead-content phosphate glasses are the smallest observed thus far for metaphosphate glasses with divalent network modifier cations.     

Boson peak,structural inhomogeneity,light scattering and transparency of silicate glasses

The microscopic origin of the excess of Density of Vibrational States (Boson peak) is discussed, taking into account recent analyses of the properties of glasses that were frozen-in under high pressure. Experimental data reveals a decrease of the Boson peak with increasing pressure of freezing (fictive pressure) and, simultaneously, an increase of the structural homogeneity of the glass. These results suggest new ways to improve the transmission of telecommunication fibers by decreasing the optical loss due to the scattering by the structural inhomogeneities of glasses.     

Glasses in the system of MnNbOF5–BaF2–BiF3–ErF3

The glasses in the MnNbOF₅–BaF₂–5BiF₃–ErF₃ system were obtained and their thermal and optical properties were studied. The specialties of crystallization depending on system composition are showed. The glass structure is discussed based on results of the IR and Raman spectra study. During the studies of inelastic light scattering, there revealed a strong photoluminescence, produced by erbium emission, whose intensity depends not only on the erbium trifluoride content in glass, but also on the glass network structure.     

Effect of fictive temperature on the optical absorption of cobalt (II) and nickel (II) in some phosphate glasses

The optical absorption of cobalt (II) in Na₂O, 4P₂O₅ melts and in H₂ONaCl mixtures has been studied at different temperatures; the equilibrium: octahedral ? tetrahedral shifted towards the right with increasing temperature in both solvents. The optical absorption of cobalt (II) and nickel (II) has been studied in a series of metaphosphate glasses: Na₂OCaOP₂O₅, and it has been shown that the equilibrium octahedral/tetrahedral ratio of these ions measured at room temperature can be correlated with the transformation temperature of these glasses. The colour of cobalt (II) or nickel (II) containing CaO·P₂O₅ glasses has been found to be significantly dependent on thermal history; the intensity of optical absorption changed reversibly on heat treatment at the transformation range of the glass.     

Optical constants of As2Se3–Ag4SSe–SnTe amorphous thin films

Amorphous thin films from the As₂Se₃–Ag₄SSe–SnTe system were prepared by thermal vacuum evaporation from the corresponding bulk glasses. Their transmission, reflection, scattering and ellipsometric spectra were measured in the UV, VIS and NIR regions, and the results were mathematically simulated using the Tauc–Lorentz dispersion model in order to obtain the refractive index and extinction coefficient. The compositional dependence of the derived optical properties was found and discussed.