M. S. Blanter

Neutron studies of structural changes in amorphous C60 fullerite under temperature, pressure, and thermobaric effects

The structural behavior of amorphous fullerites obtained as a result of mechanical activation and thermal, baric, and thermobaric effects is studied via neutron diffraction. It is shown that the phase transition between the molecular crystal (fullerite) and atomic crystal (graphite) phases in the nanoscale state occurs through intermediate amorphous phases.

Neutron diffraction study of interaction between amorphous and crystalline C60 fullerenes and aluminum

The interaction between amorphous and crystalline C60 fullerene (20–40 wt %) after thermobaric treatment at temperatures of up to 630°C at a pressure of 70 MPa is studied by means of neutron diffraction. Amorphous fullerene is prepared via mechanical grinding. It is shown that a dense composite is formed with a density to within 10% of the theoretical value and hardness several times greater than that of aluminum.

Neutron diffraction study of the interaction of iron with amorphous fullerite

The amorphous fullerite C60 has been prepared by mechanical activation (grinding in a ball mill), and its interaction with iron during sintering of powders with 0–95 at % Fe has been studied. After sintering in the range 800–1200°C under a pressure of 70 MPa, the samples have nonequilibrium structures different from the structures of both annealed and quenched steels. In this case, the carbon phase, i.e., amorphous fullerite, undergoes a polyamorphous transition to amorphous graphite. It has also been shown that the interaction of amorphous fullerite with iron is weaker compared to crystalline fullerite or crystalline graphite.

Ab Initio Based O-O Investigation and the Snoek Relaxation in Nb-O

t is common knowledge that interstitial-interstitial interaction influence on the Snoek relaxation. We used a computer simulation of this effect in the Nb-O alloy to test the adequacy of various models of the O-O interaction and clarify the mechanism of this effect The energy calculations in the first twelve coordination shells have been performed by the projector augmented-wave (PAW) method as implemented in the Vienna ab initio simulation package (VASP). The energies have been calculated in different ways which vary in the method of determination the energy of non-interacting O-O pairs. The energies calculated on the various variants are similar but in one case there is O-O repulsion in all first twelve coordination shells, whereas in another one can see attraction in four of twelve shells. Internal friction Q-1was calculated as a sum of the contributions from individual interstitial atoms in different environments, each of which being assumed to be the Debye function. It is assumed that long-range interaction of oxygen atoms affects the distribution of these atoms and the energy of each interstitial atom in the octahedral interstices before a jump and after a jump. The Monte Carlo method is used for simulating short-range order of interstitial atoms and for calculating values of energy changes. Comparison of the calculated temperature and concentration dependence of the Snoek peak with the published data showed that the PAW supercell calculation of the O-O interactions in Nb describes the behavior of the interstitial solid solution adequately. It proves also that the impact of interstitial atom concentration on the Snoek relaxation is connected to the mutual attraction of these atoms.

Interaction of Interstitial Nitrogen Atoms in Nb: Ab Initio Calculations

Ab initio calculations of pair nitrogen interstitials interaction in the first 12 coordination shells of a Nb crystal lattice are performed using the Vienna ab initio simulation package (VASP), and chemical and strain-induced contributions are analyzed. It is shown that rapidly decreasing chemical repulsion prevails in the nearest coordination shells, whereas strain-induced (elastic) interaction makes the main contribution in more distant shells.

Effect of deuterium on phase transformations in fullerenes at high temperatures and high pressures

The effect deuterium has on phase transformations is studied for amorphous and crystalline fullerenes C60 and C70 at high temperatures of up to 1300°C and high pressures (2–8 GPa). Amorphous fullerene phases are obtained via long grinding in a planetary mill. Structure is studied by means of neutron diffraction. In all cases, amorphous graphite (nanographite) forms in the temperature range of 800–1100°C. This material has different diffraction spectra distinguished by the heights of the halos observed on the graphite diffraction maxima and their relative intensities. These spectra (the structure of nanographite) are affected by preliminary amorphization, the number of carbon atoms in the fullerenes (C60 or C70), and the introduction of deuterium atoms. The different spectra of amorphous (disordered) graphite testify to its varying structure.

Neutron diffraction study of metal-matrix composite with fullerite

Interaction of amorphous fullerite C60 with austenitic Fe-33.2 wt. % Ni alloy at pressures 0-8 GPa and temperatures 600-1100 °C was studied by neutron diffraction. The amorphous fullerite was obtained by ball milling and mixed with the powder of the crystalline alloy. The interaction at sintering led to the dissolution of carbon in fcc Fe-Ni solid solution and the formation of carbide (Fe, Ni)3C, but the Fe-Ni-C alloy did not undergo phase transformations and preserved the original fcc structure. As a result, the alloy hardened, we could also witness a clear barometric effect: at the pressure of 2 GPa the amount of the dissolved carbon and the microhardness turned out to be significantly higher than those at 8 GPa. During sintering amorphous fullerite is undergoing phase transitions and its microhardness is higher than the microhardness of the metal component. At high temperatures of interaction graphite appears. The presence of Fe-Ni alloy in the composite reduces the temperature of graphite formation in comparison with transformations in the pure amorphous fullerene.

Ordering in V-O and V-N Solid Solutions: Computer Simulation

The atomic structures of interstitial solid solutions O and N in V at relatively low concentrations O(N)/V = 1/16 or 1/8 are calculated using the Monte Carlo method. A combined model of long-range interaction between interstitial atoms is employed. The first 12 shells contain ab initio energies and the energies in shells 13–18 are calculated on the basis of a phenomenological model of deformation interaction. The ordered solid solutions are long-period structures with body-centered tetragonal crystal lattices and tetragonality c/a < 1.