Thiosilicate and selenosilicate glasses are the sulfide and selenide counterparts of the well-known silicate glasses. This paper reviews the main investigations carried out to shed light on the structural, thermal and electrical characteristics of these glasses, showing their particularities compared to their oxide counterparts, such as a more complex structure with the presence of both, corner- and edge-sharing tetrahedra and much higher ion conductivity due to the larger polarizability of the chalcogen and the more covalent nature of the bonds, but also, their similarities with the presence of both, bridging and non-bridging S or Se or the existence of a mixed alkali effect when two mobile Li + and Na + cations coexist in the glassy network. Structural consequences of competition between SiS 2 and another former, GeS 2 , PS 5 / 2 or BS 3 / 2 are also discussed.

The atomic scale structure of amorphous AsTe₃ is investigated through X-ray diffraction, first-principles molecular dynamics (FPMD), and machine learning interatomic potentials (ML-GAP) obtained by exploiting the ab initio data. We obtain good agreement between the measured and modelled diffraction patterns. Our FPMD results show that As and Te obey the 8-N rule with average coordination numbers of 3 and 2, respectively. We find that small fractions of under and over coordinated As and Te atoms are present in the amorphous phase with about 6% (FPMD), and 13% (ML-GAP) of 3-fold Te. As is found at the center of pyramidal structures predominantly linked through Te_n chains rather than rings. Despite the low As concentration in AsTe₃, its local environment features a very high chemical disorder that manifests through the occurrence of homopolar bonds including at least 57% of As atoms.

The transition from a semiconductor to a fast-ion conductor with increasing silver content along the Ag _x (Ge _0.25 Se _0.75 ) _{(100− x )} tie line (0≤ x ≤25) was investigated on multiple length scales by employing a combination of electric force microscopy, X-ray diffraction, and neutron diffraction. The microscopy results show separation into silver-rich and silver-poor phases, where the Ag-rich phase percolates at the onset of fast-ion conductivity. The method of neutron diffraction with Ag isotope substitution was applied to the x =5 and x =25 compositions, and the results indicate an evolution in structure of the Ag-rich phase with change of composition. The Ag–Se nearest-neighbours are distributed about a distance of 2.64(1) Å, and the Ag–Se coordination number increases from 2.6(3) at x =5 to 3.3(2) at x =25. For x =25, the measured Ag–Ag partial pair-distribution function gives 1.9(2) Ag–Ag nearest-neighbours at a distance of 3.02(2) Å. The results show breakage of Se–Se homopolar bonds as silver is added to the Ge _0.25 Se _0.75 base glass, and the limit of glass-formation at x ≃28 coincides with an elimination of these bonds. A model is proposed for tracking the breakage of Se–Se homopolar bonds as silver is added to the base glass.

We report on pressure-induced phase transitions in the ${\mathrm{Sb}}_2\mathrm{Te}$ and ${\mathrm{Ag}}_{11}{\mathrm{In}}_6{\mathrm{Sb}}_{55}{\mathrm{Te}}_{28}$ (AIST) phase change alloys used in optical recording media over a pressure range from ambient pressure to 40 GPa. The results clearly demonstrate the crucial role of dopants in sequences of high-pressure structural transformations and in the degree of reversion. We also demonstrate that prolonged exposure of AIST to high pressures leads to an additional phase transition that may have fatal consequences for process reversibility in repeated compression/decompression cycles. DOI: http://dx.doi.org/10.1103/PhysRevB.83.024105 © 2011 American Physical Society

The structural, vibrational and electronic properties of several compositions of amorphous Ge-Se-Te are studied from a combination of x-ray diffraction and density functional-based molecular dynamics. Different structural properties are considered such as structure factors, pair distribution functions, angular distributions, coordination numbers, and neighbor distributions. We compare results with experimental findings and a satisfying agreement is found for the structure functions in real and reciprocal spaces. The short range order is found to be more complex than in related binaries that result in mixed geometries ($\simeq 65\%–75\%$ tetrahedral, and remaining defect octahedral) for a dominant fourfold Ge (80%). The chalcogen atoms are dominantly twofold, the former having furthermore an important fraction of threefold coordinated atoms (30%–40%). The obtained model structures indicate that Ge-Ge, Ge-Se, and Ge-Te bonds dominate with small fractions of Te-Te bonds remaining from the base system GeTe. The investigation of electronic properties indicates that the addition of Se atoms will lead to Te-related bands that are much more localized so that Ge-Te-Se can be regarded as having an increased covalent character with respect to GeTe.