Binary glasses in the sodium fluoride beryllium fluoride and soda silica systems have been studied previously using neutron diffraction and, in the present paper, the features in the real space correlation function, corresponding to the first A–X (A=Be, Si; X=F, O) and Na–X interactions are compared for the two systems. The first A–X peak shifts to significantly higher r for Na 2 O–SiO 2 but not for NaF–BeF 2 and it is concluded that this is an effect of charge balance. In both cases the Na–X peak is skewed to high r due to the presence of two types of Na–X distance.

Previous experiments have demonstrated unambiguously that a small fraction of the hydrogen in hydrogenated amorphous silicon is present as H-2 molecules trapped in the cages of the amorphous network. In the present paper, small angle neutron scattering (SANS) is employed to investigate the size of the cages containing the H-2 molecules and yields a mean radius of similar to 6.5 Angstrom. The use of H-D contrast techniques indicates that each cage contains, on average, about 60 H-2 (D-2) molecules. Data are also reported for a partially fluorinated sample and are consistent with a previously suggested model of network cages predominantly containing molecular SiF4.

High-resolution neutron-diffraction data have been collected on PbO-GeO2 glasses and on GeO2 for comparison. These neutron data have revealed the existence of 6-fold coordinated Ge (GeO6 octahedra) by virtue of the shift in the first peak in the total correlation function T(r) and increase in coordination. The neutron results also indicate that PbO exits as PbO4 pyramids, as found in the orthorhombic form of PbO crystal, in PbO-GeO2 glasses.

A series of model steels and commercial alloys from the IAEA Phase 3 irradiation programme was irradiated to a dose of 14 mdpa (∼ 9 × 1022 n m−2 (E > 1 MeV)) at 290°C. The steels were examined using small angle neutron scattering and a range of transmission electron microscope techniques. Measured yield stress and hardness changes were interpreted in terms of the irradiation-induced microstructural developments. The irradiation of Cu-containing steels produced Cu-rich precipitates of ∼ 2 nm diameter which were alloyed with Mn and Ni. The Ni content of the precipitates increased markedly for bulk Ni contents > 0.7 wt%. The volume fractions of precipitate increased with increasing bulk Cu content and, also, with increasing bulk Ni content > 0.7 wt%. The precipitate-induced strengthening and hardening varied according to the square root of the volume fraction of precipitate. Yield stress changes in low-Cu steels were consistent with data from the IAEA Phase 2 irrradiation programme.

Inelastic neutron scattering, Raman scattering and model calculations play complementary roles in the understanding of the vibrational modes of amorphous solids. These roles are illustrated by new and recent results for vitreous B2O3 from both inelastic neutron scattering and modelling. The well known boroxol ring breathing mode is clearly observed in the neutron data which show the mode to be enhanced in the Raman HV and HH spectra by factors estimated at 6.3 and 40, respectively. The observed width of the mode (FWHM 1.7 meV) is comparable with the resolution of the measurement (1.6 meV). This width could not be fully reconciled with Raman results. Full details are given of modelling studies of the vibrational density of states of ball-and-stick models which take into account non-central forces. In these studies, indirect methods have been developed for probing the nature of the calculated modes by considering the study of the effects of force constant variation and of isotopic substitution.

Although the nuclear magnetic resonance (NMR) and neutron diffraction evidence for the majority of the boron atoms in vitreous boron oxide being involved in boroxol groups would seem to be irrefutable, nevertheless several recent papers have challenged this conclusion. The present paper, therefore, examines these claims in the light of neutron diffraction data, with much greater accuracy than those reported previously, and of neutron inelastic scattering results, optimised to give the highest possible energy transfer resolution in the region of the boroxol ring breathing mode. A fit to the interference function, Qi(Q), indicates that the fraction, f, of boron atoms in boroxol groups is 0.80 ± 0.05, while the neutron weighted density of states exhibits a well resolved boroxol ring breathing mode of similar magnitude to the theoretical prediction for a structural model with f = 0.75. Both results confirm the conclusion of the earlier NMR and neutron studies.

A short summary is presented of inelastic neutron scattering studies of hydrogenated and deuterated amorphous silicon with particular emphasis on the structural role played by the hydrogen (deuterium) atoms. It is concluded that the data are consistent with the existence of molecular H-2 (D2) trapped within the cages of the amorphous covalent network.

High energy resolution S(Q, E) measurements on g-SiO2 clarified the details of the VDOS, showing additionally a broad hump at 69 meV and weak sharp peaks at 63 meV and 77 meV. The paper discusses the Q dependence of the VDOS using a model and presents a dynamical pair correlation function.

Neutron diffraction and magic angle spinning (MAS)-NMR measurements have been performed on vitreous silica before and after irradiation to a dose of 2.8×1020 fast neutrons cm−2. On fast neutron irradiation the first peak in the diffraction pattern is reduced in height, broadened and shifted to a slightly higher scattering vector, reflecting the increase in density of 2.4%. This may be interpreted as an enhancement of smaller scale structures, consistent with irradiation generating a higher proportion of three-membered rings as indicated by Raman data. In real space, there is a corresponding small increase in the SiO bond length which is consistent with a reduction in the mean SiOSi bond angle of ≈9.5° as indicated by the MAS-NMR data. Fast neutron irradiation also leads to a peak in the difference correlation function at ≈3.2Å which has previously been ascribed to oxygen atom interstitials, but may be identified as the Si(2)O distance within a three-membered ring.

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.

A report is given of a new inelastic neutron scattering measurement for vitreous SiO2 made with a high energy resolution and a wide and continuous range of momentum transfer. The use of a real-space correlation function in the interpretation of the Q-dependence of the scattering function is investigated.

The magnetic small angle neutron scattering for amorphous Dy7Ni3 at low temperatures has been measured. There is evidence of transitions at 35 and 150 K. The behaviour above 35 K is consistent with previous studies of random anisotropy magnetism but it deviates from this at temperatures below 35 K.

Hydrogen is well known to play an important role in the electronic properties of hydrogenated amorphous silicon, a-Si:H. However, its precise location and thus the a-Si:H local order still remain uncertain. The aim of the present study, using the complementarity of steady state and pulsed neutron sources, is to provide accurate data concerning the short range order.

Medium range order in three Gex Se1−x glasses has been studied by the inelastic scattering of low energy neutrons. The main GeSeGe bond angle stretching mode of GeSe2 is observed as a major feature in the generalised density of states but the Raman ‘companion line’, which has been associated with either edge-sharing tetrahedra or a vibrational mode of the SeSe bonds on the edges of “outriggers rafts”, is not resolved as a separate peak. Limits are set for the relative strength of this vibration. Low frequency modes are observed for all three alloys as a shoulder in the density of states which increases in magnitude and energy as x is decreased. The Q dependence of these modes in GeSe2 indicates that they arise from the rotational motion of coupled tetrahedra.

We report neutron diffraction measurements of liquid bromine at T = 298 K and T = 473 K and orthobaric densities. The structure factor, S(Q), in the range 0·8–15Å-1 and the non-bonded bromine atom-atom correlation function, g(r), are discussed and compared with previous results on Br2 and Cl2. Monte Carlo (MC) computer simulations using the two-centre Lennard-Jones interaction model with idealized point quadrupole were performed at the higher temperature. This effective pair potential turns out to be unable to reproduce the Br2 structure.

Etude par diffraction de neutrons a partir d'une methode de double substitution isotopique qui s'est averee extremement puissante

It is proposed that the structure of GeSe2 glass is characterized by a chemically ordered continuous random network. Within this context it is suggested that 4-atom planar rings exist and can explain an unusual feature in the Raman spectrum. Neutron scattering data are presented which supportthis model.

High resolution X-ray and neutron correlation functions have been obtained for arsenic sulphide bulk glass and vapour-deposited films by making measurements to high momentum transfers. These data are compared with a vatiety of models and it is concluded that the structure of the films is dominated by the presence of As4S4 molecules in the vapour phase, which results in more As-As bonds than the minimum required by stoichoimetry. The extent to which these As4S4 molecules polymerise in the as-deposited film is unclear, but depends strongly on preparation conditions.

Thermal neutrons from steady-state (reactor) and pulsed (linac) neutron facilities have been used to study the structure factor for liquid bromine at 20°C, covering a wide range of values (0·6-35 Å-1) of the momentum transfer (ħQ). The diffraction pattern at high Q-values (>10 Å-1) gives information on the structural properties of the individual molecules but detailed interpretation is complicated by the vibrational motion which causes a systematic variation in the periodic oscillations of the molecular form-factor. An internuclear distance (bond length) of 2·28 ± 0·01 Å is found to be suitable for data at lower Q-values and has been used in the analysis of the liquid structure. The results show that some form of orientational correlation between molecules must be present and the nuclear (atom) pair correlation function is split into two peaks for the coordination shell corresponding to nearest-neighbour molecules. The results are compared with other studies of liquid bromine and similar neutron experiments for liquid nitrogen and liquid oxygen.