Bonding trends within ternary Isocoordinate chalcogenide glasses GeAsSe

A structural study is presented of ab-initio molecular dynamics simulations of Ge-As-Se calcogenide glasses performed at the same mean coordination number but differing stoichiometry ranging between Se rich and Se poor glasses. Starting configurations are generated via Reverse Monte Carlo (RMC) simulations of Extended X-ray Absorption Fine Structure (EXAFS) measurements of experimental samples. Structural analysis is presented illustrating the bonding trends found with changing stoichiometry.Comment: 26 pages, 9 figures. Submitted to Physical Review

L-edge XANES analysis of photoexcited metal complexes in solution

Ultrafast X-ray absorption spectroscopy is a powerful tool to observe electronic and geometric structures of short-lived reaction intermediates. The ab initio FEFF9 code is applied to simulate the Pt L-3-edge XANES spectrum of the photocatalytic diplatinum molecule [Pt-2(P2O5H2)(4)](4-) and the photo-induced changes that occur therein. The spectra are interpreted within a XAFS-like scattering theoretical framework (bound-continuum transitions) or in terms of a final-state local l-projected density of states (LDOS) (bound-bound transitions). By using a novel Bayesian fitting procedure, we show that the ground-state structures obtained independently from the XANES and EXAFS regions of the spectrum are in good agreement with each other. The semi-quantitative result obtained for the Pt-Pt contraction in the excited state is in line with recently published values. The improved theoretical treatment of inelastic losses has shown to result in more accurate peak positions in the above-continuum region of the spectrum which is an important prerequisite for obtaining quantitative structural information from (time-resolved) XANES spectra

Thermal and structural modification in transparent and magnetic germanoborate glasses induced by Gd2O3

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO2–25B2O3–10Na2O–4Al2O3–1PbO] – (x) Gd2O3, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd2O3. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd2O3 showed a high thermal stability, which progressively decreases for samples with higher content of Gd2O3. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd2O3, a progressive depolymerization of 6-membered Ge[IV] rings is promoted, concomitant with an increase of Ge[IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd3+ does not change with the addition of Gd2O3 and the presence of germanium four-fold coordination [GeIV] and Gd3+ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge–O and Gd–O bonds and the Debye-Waller factor was also carried out. The microstructure, after crystallization, of the sample with 15 mol% of Gd2O3 was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd3+ ions were obtained based on magnetic susceptibility measurements