Accurate comparative measurements have been made of the X-ray diffraction pattern of a bulk arsenic sulphide glass prepared from the melt and a 250 μm film prepared by vapour deposition of the evaporated bulk. By using Ag Kα radiation, measurements have been made up to Q = 21 Å−1 (Q = 4π sin θ/λ) so as to give good spatial resolution. Significant differences are found between bulk and film specimens, and in particular a shoulder is found on the high r side of the first peak in the distribution function for the film. Also, the film is richer in arsenic than the parent bulk. The results are compared in detail with a number of models, all of which involve covalent bonding requirements being fully satisfied, and it is concluded that there are more AsAs bonds in the film than the minimum required by stoichiometry and that a significant fraction (≈23) of these are unusually long (≈2.6 Å compared to the more usual 2.5 Å). The most probable explanation is that the vapour contains a significant fraction of As4S4 species (in which the AsAs distances are ≈2.6 Å) and that the film contains a mixture of molecular species which have undergone considerable polymerization. The extent to which this results in a sheet-like structure similar to that proposed for the bulk glass remains unclear.

The structures of vapour-deposited amorphous films of composition AsxSe1−x′, with x between 0 and 1, have been investigated by X-ray diffraction. In all cases the structure of the freshly deposited film differs very considerably from that of the corresponding bulk glass. For the elemental amorphous films the structure is highly disordered and contains voids which for Se cannot be annealed out below the crystallization temperature of 70°C or, for As, below the temperature (⪆130°C) where the As film re-evaporated. Annealing of the arsenic selenide films at temperatures below Tg causes the structures to relax towards those of the bulk, with a distribution of activation energies around 25 kJ mol−1. The composition of the vapour has been examined by mass spectroscopy and it is concluded that even if some molecular identity is retained on condensation there must be considerable cross-linking to give the observed structural behaviour.

Abstract The structure of the orthorhombic crystal modification of arsenic has been determined from an analysis of X-ray powder diffraction data. The structure is confirmed as being similar to that of black phosphorus, with space group Bmab and eight atoms per unit cell. Each atom is covalently bonded to three neighbours, with two bonds in an ab plane, of length 2·49 A, making an angle of 94·1° and the third bond, of length 2·48 A, at an angle of 98·5° with each of the other two. The structure differs significantly from that deduced from the black phosphorus structure by a simple scaling with bond lengths. The relationship of the glass structure with the structures of both orthorhombic and rhombohedral (metallic) arsenic has been considered. The structure of the vitreous phase is much closer to that of the orthorhombic crystal. A good description of the glass structure may be obtained using a quasi-crystalline model based on this structure with some expansion of the interlayer spacing and some additional ...

Influence of oxygen presence on the crystallization behavior of (GeS2)y(Sb2S3)1-y glasses (for y up to 0.3) was studied by differential scanning calorimetry, X-ray diffraction analysis and infrared microscopy - the study was performed in dependence on particle size. The oxygen was found to significantly accelerate crystallization from mechanically induced defects for the (GeS2)0.1(Sb2S3)0.9 composition and to sustain the intensity of crystal formation in case of the (GeS2)0.2(Sb2S3)0.8 and (GeS2)0.3(Sb2S3)0.7 compositions. On the other hand, presence of oxygen influenced neither the morphology of the crystallites, nor the actual crystallization model-free and model-based kinetics. Direct microscopic observation confirmed strict surface crystallization for all studied composition. Compositional evolutions of the viscosity data and microscopically determined crystal growth rate curves have shown that it is the exceptionally high crystal growth rate and crystallization tendency (compared to the minor-to-moderate contribution of viscosity itself) that are responsible for the significant influenceability of the (GeS2)0.1(Sb2S3)0.9 crystallization by the presence of oxygen.

X-ray and neutron diffraction experiments have been performed on vitreous arsenic sulphide close to the composition As2S3 and on a series of vitreous arsenic selenides including compositions both arsenic- and selenium-rich with respect to As2Se3. The data have been analysed by direct examination of the diffraction patterns, by Fourier analysis and by comparison both with quasi-crystalline calculations based on the orpiment structure and with models of the first neighbour correlations using the experimental peak functions. Sheet structures occur in all the glasses, the sheet separations being larger than in the corresponding orpiment structures, and the intersheet correlation perpendicular to the sheets extends for 15 Å in arsenic sulphide and 20 Å in arsenic selenide. For the selenide glasses the sheet structure becomes more pronounced with increasing arsenic concentration. For all the glasses the data are consistent with full satisfaction of the respective two- and threefold covalency requirements of chalcogenide and arsenic atoms, excess atoms being incorporated into the structure by the formation of covalent bonds between like atoms. The distribution of arsenic-chalcogen bond lengths is shown to be symmetrical about the average values of 2.24 Å and 2.44 Å for sulphide and selenide respectively. In the selenide glasses close to the As2Se3 composition, the average first SeSe distance is 3.65 Å. The advantages and limitations of the experimental and analytical techniques employed are discussed and a simple model based on steric considerations is advanced to account for the influence of arsenic concentration on the inter-sheet correlation.