Changes in the structure and atomic dynamics of diamond irradiated by fast neutrons have been studied. It has been shown that a sample irradiated to a fluence of 1021 cm−2 holds the diamond crystal structure and change in the cubic cell parameter corresponds to a 5% increase in the atomic volume, which can be treated as the application of a “negative” pressure P < −25 GPa to the sample. It has been found experimentally that a peak in the phonon spectrum corresponding to optical modes of a crystal lattice is noticeably shifted toward low energies. The Grüneisen parameter for optical modes of diamond at negative pressure has been estimated. It has been established that the Grüneisen parameter of diamond in the pressure range of −25 GPa < P < 35 GPa does not change and is close to unity.

Diamond preliminary damaged with neutrons was irradiated with swift heavy ions (SHI, 1030 MeV Bi-209) decelerated in the electronic stopping regime as well as with fs-laser pulses. The initial excess electronic energy densities appearing in the nanometric vicinity of the SHI trajectories and within the absorbing layers in laser spots were comparable (similar to 10(24) eV cm(-3)). Graphitization of diamond in the central parts of the lased spots was observed above the threshold fluence of 15-30 J/cm(-2). It was also found that the lower threshold fluence is required for initiating graphitization as well as destruction of the pre-damaged crystal by laser pulses in comparison to that for undamaged diamond. This indicates a noticeable effect of an existing defect ensemble on the kinetics of diamond transformations in laser spots. However, X-ray diffraction, atomic-force microscopy, and electron microscopy detected no graphitic domains within the SHI-irradiated pre-damaged crystal. The research demonstrated that the density of the initial excess electronic energy cannot be treated as the sole parameter governing subsequent structure transformations in diamond. Large differences between the spatial as well as temporal scales finally results in different pathways of the relaxation kinetics of this excess energy in laser spots and SHI tracks in diamond.

The average kinetic energy 〈E(T)〉 of the atomic nucleus for each element of the amorphous alloy Zr40Be60 in the temperature range 10–300 K has been measured for the first time using VESUVIO spectrometer (ISIS). The experimental values of 〈E(T)〉 have been compared to the partial ZrBe spectra refined by a recursion method based on the data obtained with thermal neutron scattering. The satisfactory agreement has been reached with the calculations using partial spectra based on thermal neutron spectra obtained with recursion method. In addition, the experimental data have been compared to the Debye model. The measurements at different temperatures (10, 200, and 300 K) will provide an opportunity to evaluate the significance of anharmonicity in the dynamics of metallic glasses.

Positions of local and quasi-local impurity frequencies in metallic alloys have been considered. It has been shown that the differences between the frequencies calculated in the isotopic approximation and the experimental values can be explained not only by a change in the force constants (force shifts), as it is usually done, but also by a change in the effective mass of the oscillations (mass shifts). Comparison of the calculations with the experimental data demonstrates that the main role in the difference between the frequencies calculated in the isotopic approximation and the experimental values is played by the mass shifts rather than the force shifts, at least for local modes.

The thermal stability and structure of binary amorphous Zr 100 − x Be x alloys have been studied using differential scanning calorimetry and neutron diffraction over a wide concentration range (30 ≤ x ≤ 65). The amorphous alloys have been prepared by rapid quenching from melt. The studied amorphous system involves the composition range around the eutectic composition with boundary phases α-Zr and ZrBe 2 . It has been found that the crystallization of alloys with low beryllium contents (“hypoeutectic” alloys with x ≤ 40) proceeds in two stages. Neutron diffraction has demonstrated that, at the first stage, α-Zr crystallizes and the remaining amorphous phase is enriched to the eutectic composition; at the second stage, the alloy crystallizes in the α-Zr and ZrBe 2 phases. At higher beryllium contents (“hypereutectic” alloys), one phase transition of the amorphous phase to a mixture of the α-Zr and ZrBe 2 phases has been observed. The concentration dependences of the crystallization temperature and activation energy have been revealed.

A high-resolution (1.5 meV) inelastic neutron scattering experiment is carried out to investigate in detail the low momentum (0.6–1.5 Å−1) dynamic response in Zr50Be50 metallic glass. The results are obtained on the hot neutron three-axis spectrometer IN1 in the Laue-Langevin Institute (Grenoble, France). A comparison with recent neutron scattering results for the momentum transfer region above 1.4 Å−1 shows a minimum in the dispersion relation of low energy excitations near the prepeak of the static structure factor. These excitations appear to be due to the short-range order in this amorphous system.

Hydrogen induced structure transformations in amorphous alloys ZrPd, ZrRh and ZrRhBe were studied by neutron and X-ray-diffraction technique under gas pressure up to 2 kbar. It was shown that the amorphous alloy Zr(0.7)Pd(0.3) which was hydrogenated at temperature below the temperature of crystallization decomposes into metastable hyper-stoichiometric Pd-hydride with bcc lattice and amorphous hypo-stoichiometric Zr-hydride. The polyamorphous transition (transition between the amorphous phases) was reversible while the formation of metastable phase was not. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

The atomic structure and the dynamics of Cu1 − x Fe x samples (x = 0.15, 0.5, and 0.85) obtained by melt spinning from the elements that are immiscible under standard conditions has been investigated. The change in the physical properties of the system obtained in this way is due to the formation of nanocrystallites.

The dynamic structure factors, S(Q, E), for the Zr70Be30, Zr60Be40 and Zr50Be50 metallic glasses have been measured using neutron inelastic scattering on the IN4 spectrometer (ILL, Grenoble, France), over the range of momentum transfers 0.7 < h Q (angstrom(-1)) < 7 and energy transfers 2 < E (meV) < 60. The constant- Q cuts through the dynamic structure factor and longitudinal current correlation function, J(l) ( Q, E), were obtained. The dispersion relations for two representations, S( Q, E) and J(l) (Q, E), were derived by fitting a Gaussian to the peaks. The specific low-energy modes (similar to 5 meV) as well as 'acoustic-phonon like' (similar to 16 meV) and 'optic-phonon like' excitations (similar to 47 meV) were observed in these metallic glasses with disparate mass and ionic radius components.

The dynamic structure factors, S(Q, E), for Ni42Nb58 metallic glass have been measured using neutron inelastic scattering on the IN4 spectrometer (ILL, Grenoble, France), over a range of momentum transfer, 0.7 < hQ/angstrom(-1) < 8, and energy transfer, 2 < E/meV < 50. Three samples with the same chemical composition and different Ni isotope content were investigated. The constant-E and constant-Q cuts through the S(Q, E) functions have been obtained. They reveal the E-and Q-dependencies due to the existence of the collective vibrational excitations in Ni42Nb58 glass. At the same time the difference of Ni and Nb atoms dynamics was observed by isotope contrast in the scattered spectra. (c) 2007 Elsevier B.V. All rights reserved.

The dynamic structure factor S ( Q, E ) of Ni 2 B metallic glass was studied by inelastic neutron scattering in the ranges of momentum transfers 0.7 < ħQ /Å −1 < 7, and energy, 2 < E /meV < 70, transfers. The measurements were performed with the IN4 spectrometer (Institut Laue-Langevin (ILL), Grenoble, France) on three samples of the same chemical composition but with different contents of Ni and B isotopes, as a result of which partial contributions were determined. The cuts through S ( Q, E ) for different values of E and Q demonstrated a characteristic behavior indicating that vibrational excitations, similar to acoustic and optical phonon excitations in crystals, propagate in an amorphous medium in a certain energy and momentum range.

Composites of Cu and Pb (immiscible in solid state) were prepared by melt spinning onto a copper disc. X-ray diffraction measurements showed the Cu-Pb composites thus obtained to consist of Pb nanoparticles of a certain size embedded in a copper matrix. The average size of the nanocrystalline Pb blocks was determined along the normals to the (111) and (200) reflecting planes, and their size distribution was measured. The vibrational, electronic, and superconducting properties of the Cu 85 Pb 15 and Cu 50 Pb 50 composites were derived from low-temperature heat-capacity, magnetic-susceptibility, and resistance measurements, and the contribution of Pb nanoparticles to the heat capacity was separated. The low-frequency excitation density in Pb nanocrystals was found to increase as compared to that in crystalline Pb. The observed decrease of T c correlates with the variation of Pb nanoparticles in size, which is a consequence of the size effect in the properties of Pb nanocrystals.

Molecular dynamics is used to investigate the coagulation of the precipitates in a supersaturated binary solution and its dependence on the thermodynamic properties of the system, concentration and temperature. Lennard–Jones potentials with different parameters for different pairs of atoms are employed. Coagulation proceeds by gradual growth of clusters and is not a thermally activated process. The rate of coagulation depends weakly on temperature. Solute clusters are initially amorphous and crystallize in the stable face-centered cubic structure only after reaching a specific size.

The vibrational, electronic, and superconducting properties of a Cu 90 Nb 10 nanocrystalline composite undergoing a transition from a coarse-grained state to a nanocrystalline state are investigated using neutron scattering and low-temperature heat capacity measurements. It is found that, compared to a coarse-grained sample, the nanocomposite is characterized by a higher density of low-frequency excitations and a decrease both in the density of states and in the superconducting transition temperature due to the size effect.

Diffraction data are used to develop 300-K models of the amorphous Ni62Nb38 and Ni44Nb56 alloys using a “hybridization” algorithm, in which the force functions for each atomic pair are linear combinations of those generating the structure of the alloy at 0 and 300 K. These force functions are found using the Schommers algorithm at 300 K and the “coordination number comparison algorithm” (proposed in this work) at 0 K. The pair correlation functions thus found agree well with the diffraction data. The calculated vibrational densities of states for the Ni and Nb atoms in the amorphous alloys studied are in reasonable agreement with inelastic neutron scattering data. The calculated heat capacity of Ni62Nb38 agrees well with experiment, while that of Ni44Nb56 is lower than the reported values.

The inelastic neutron scattering intensity, I(E,Ω), for Ni62Nb38 metal glass has been measured over a wide range of scattering angles, Ω=13°–120° , and energy transfer, E=−10–+50 meV. Three samples with the same chemical composition and different Ni isotope content have been investigated. This allowed us to reconstruct three partial inelastic scattering functions INiNi(E,Ω), INbNb(E,Ω), and INiNb(E,Ω), according to the Ashcroft–Langreth formalism. The propagating excitations in a two-component amorphous alloy are the result of the superposition of three partial excitations. Each of these excitations is given by the corresponding partial atomic distribution. The “acoustic-phonon-like” dispersion relation is observed up to Q=6.5 A−1, which is the limit accessible in the present experiment.

The specific heats of the amorphous systems Ni 44 Nb 56 , Ni 62 Nb 38 , and Cu 33 Zr 67 were studied in the temperature range 3–273 K. The data obtained allow one to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, to determine the density of electronic states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ over a broad temperature range, and to calculate a few frequency moments that characterize the vibrational spectrum. The information derived on the average characteristics of vibrational spectra is in good agreement with earlier data on inelastic neutron scattering. In transferring from Ni 44 Nb 56 to Ni 62 Nb 38 , the density of electronic states at the Fermi level decreases and the characteristic vibrational frequencies increase. The density of electronic states at the Fermi level for Cu 33 Zr 67 is close to that for Ni 62 Nb 38 . The characteristic frequencies of the vibrational spectrum of the Cu 33 Zr 67 system are substantially lower (by 30%) than those of the Ni 44 Nb 56 and Ni 62 Nb 38 systems.

The specific heats of the amorphous systems Ni44Nb56, Ni62Nb38, and Cu33Zr67 were studied in the temperature range 3–273 K. The data obtained allow one to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, to determine the density of electronic states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ over a broad temperature range, and to calculate a few frequency moments that characterize the vibrational spectrum. The information derived on the average characteristics of vibrational spectra is in good agreement with earlier data on inelastic neutron scattering. In transferring from Ni44Nb56 to Ni62Nb38, the density of electronic states at the Fermi level decreases and the characteristic vibrational frequencies increase. The density of electronic states at the Fermi level for Cu33Zr67 is close to that for Ni62Nb38. The characteristic frequencies of the vibrational spectrum of the Cu33Zr67 system are substantially lower (by 30%) than those of the Ni44Nb56 and Ni62Nb38 systems.