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Low-Energy Ion-Scattering ( LEIS) spectroscopy is a technique with a unique sensitivity to the elemental composition of the top atomic layer of a solid surface. LEIS measurements of ternary silicate glasses modified with Na2O, Cs2O, CaO, and BaO show that the compositions of the as-cast (melt) surface and the in-vacuum fracture surface often differ. While the as-cast surface is usually depleted of alkali ions (Na+ or Cs+) compared to the nominal (batch) glass composition, there is often strong accumulation of the same mobile cations on the fresh fracture surface. Depth profiles obtained by sputter etching reveal elemental concentration gradients normal to the glass surface. The final concentrations often fail to reach the nominal glass composition, suggesting the likely presence of preferential sputtering effects and thereby the distortion of the measured concentration gradient. At present, the lack of reliable standards and preferential sputtering effects in the LEIS of multicomponent glasses limit somewhat the absolute chemical composition and structural information that can be obtained with this otherwise unique and powerful method of surface analysis. [ABSTRACT FROM AUTHOR]

We have investigated devitrification of glasses within infrared transmitting x SbSI-(100 − x) Sb2 S3 pseudo-binary series, which forms SbSI and Sb2 S3 ferroelectric crystal phases. Differential scanning calorimetry ( DSC) and X-ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one-dimensional crystallization at low temperature which starts from the sample surface, and three-dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high-temperature exothermal peak to the low-temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb2 S3 phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms. [ABSTRACT FROM AUTHOR]

The structure of electrically conductive CMAS-TiO2-Pd glass and ceramics was investigated by transmission electron microscopy ( TEM), scanning transmission electron microscopy ( STEM), X-ray photoelectron spectroscopy ( XPS), X-ray absorption near-edge spectroscopy ( XANES), and extended X-ray absorption fine structure spectroscopy ( EXAFS). The XANES spectra of Ti do not show any significant difference between the glasses ceramized in air or in a reducing 'forming' gas, as well as between Pd-containing versus Pd-free samples, nor between surface versus bulk of the glass-ceramic samples. However, EXAFS and XANES data recorded at the Pd K-edge show significant dependences on whether the glass-ceramic was ceramized in air or in 'forming' gas. The XPS spectra of Ti 2 p core-level electrons for glasses ceramized in air or 'forming' gas also show a strong difference depending on whether the samples did or did not contain Pd. STEM mapping confirms the existence of grains in the form of main crystalline phases identified with XRD, and also reveals the existence of Pd nanoparticles in glasses ceramized in both air and in 'forming' gas. [ABSTRACT FROM AUTHOR]

The short-range atomic order around all three constituent atoms in a prototypical bulk metallic glass (BMG) system was probed in a complementary way, using extended X-ray absorption fine structure for neighborhood of the higher atomic number elements, and extended energy loss fine structure (EXELFS) for the lower atomic number ones. The PdxNi(80−x)P(20) system is a prototype for a whole class of BMG formers which are 80% transition metal and 20% metalloid. We find that the structure of these BMGs could be explained in terms of those of glasses at the end of the BMG range, namely, Pd60Ni20P20 and Pd30Ni50P20. The binary phosphide crystals near x=0 and 80 are found to be simulate very well the local atomic structure of Pd30Ni50P20 and Pd60Ni20P20 glasses, respectively. The best glass former in this series, Pd40Ni40P20, is best described by a weighted average of Pd30Ni50P20 and Pd60Ni20P20 structures. [Copyright &y& Elsevier]

Abstract: A previews study of germanium selenide glass films by scanning electron microscopy and atomic force microscopy revealed a heterogeneous surface morphology consisting of granular regions ∼15–50nm in size, which cause high optical losses. The present work was performed in order to further characterize such materials using spectroscopic ellipsometry, infrared (IR) and Raman spectroscopies. Chalcogenide glass films with GeSe2, Ge28Sb12Se60 and GeSe compositions have been deposited on single crystal silicon and silica glass substrates by vacuum thermal evaporation. The film thickness and the optical constants were obtained from spectroscopic ellipsometry using the Tauc-Lorenz dispersion formula. A model was derived for the film structure, which included a roughness layer at the surface. This top layer was found to have a thickness of ∼5–15nm, of the order of the size of the granular regions previously reported. The optical bandgap of the samples increased with increasing selenium content, while the refractive index decreased. Despite a previous report of large scale phase separation in bulk Ge26Sb14Se60 glass, the fundamental IR and Raman spectra obtained in the present work did not provide any clear evidence for such phase separation which could be associated with the heterogeneous nanostructure observed at the surface of the films. [Copyright &y& Elsevier]

Abstract We have investigated the occurrence of the sometimes observed grain boundaries, as initial seed is extended to form line in laser-fabricated single-crystal architecture in glass (SCAG). In particular, for Sb 2 S 3 SCAG in Sb-S-I glass as a model system, grain boundaries are formed during the transition from laser-written initial seed dot to crystal line. Such grain boundaries during the growth of Sb 2 S 3 crystals occur in 16SbI 3 –84Sb 2 S 3 glass, whereas they are absent in Sb 2 S 3 glass. We correlate this difference in tendency to form multiple grains with the relative glass forming ability i.e. the dynamics of nucleation and crystal growth as determined by differential scanning calorimetry (DSC). On the basis of this understanding, methods to minimize the appearance of grain boundaries in the transition region are suggested. Highlights • Grain boundaries can be introduced during transition from laser-written initial dot to line. • The propensity to form grain boundaries in the transition region depends on composition. • It depends on the relative glass forming ability of given composition. • A method to minimize appearance of grain boundaries in transition region is suggested. [ABSTRACT FROM AUTHOR]

A chemical compositional heterogeneity develops on glass surfaces which have experienced rapid expansion/stretching – as during the press or press/blow process used in forming. A differential etching technique using HF and HBF4 is developed to demonstrate that such heterogeneities occur on the surface of commercial articles such as soda-lime silicate tumblers. Comparison with articles exposed to aggressive conditions in a well-characterized dishwasher reveals that similar corrosion patterns appear in both cases – as alternatively corroded/non-corroded regions arranged as striations running vertically along the tumbler. Analysis of these striae by imaging ellipsometry and interferometry indicates that they consist of ridges 50–150 nm high in relief with a width and repeat distance of 0.05–0.15 mm. This pattern is in qualitative agreement with a recent physical modeling study and suggests that the ridges arise from durable low alkali glass which is at the surface of the gob/parison before the press/blow and which has been striated by less durable, high alkali glass from the interior of the gob. Under corrosive conditions, the alkali-rich glass dissolves away to leave behind the durable ridge. [Copyright &y& Elsevier]