I. O. Bashkin

Magnetic ordering in hydrofullerite C60H24

Abstract Hydrofullerites C 60 H x synthesised at hydrogen pressures of 0.6 and 3 GPa were found to possess ferromagnetic properties at room temperature. The magnitude of magnetisation varied from sample to sample and reached 0.001–0.16 Bohr magnetons per C 60 molecule at H =10 kOe. The coercivity of all the samples was about 100 Oe. The hydrofullerites had either an fcc or bcc lattice formed of C 60 H x units. The maximum values of magnetisation were observed for the fcc hydrofullerites with x ≈24.

Neutron spectroscopy of TiH0.74 after high pressure treatment

High resolution neutron scattering studies of vibrational spectra (2-800 meV) were carried out on the in -, delta and delta -phases of titanium hydride, obtained after high pressure treatment. The observed splitting of the fundamental optic peak in the delta -phase spectrum can be explained by a strong H-H interaction along the c-axis. Well pronounced features are seen on the low energy side of the two- and three-phonon optic bands. These are assigned to bound bi- and tri-phonon excitations. This is the first observation of bi- and tri-phonons in metal hydrides.

Neutron spectroscopy of fullerite hydrogenated under high pressure; evidence for interstitial molecular hydrogen

Inelastic neutron scattering spectra of a hydrofullerite quenched after synthesis at 620 K under a hydrogen pressure of 0.6 GPa, and of the same sample after annealing at 300 K for 35 h, which reduced the hydrogen content by molecules per unit, were measured at 85 K. The quenched sample is shown to consist of molecules with and of interstitial molecular hydrogen. The interstitial molecular hydrogen left the sample during annealing at room temperature, whereas the molecules were stable at this temperature. The intramolecular and intermolecular vibrations of and in the fullerite are discussed in view of the measured spectra.

Neutron scattering studies of ordered gamma -ZrD

The crystal structure and the lattice dynamics of the ordered gamma -ZrD phase were studied by means of neutron diffraction and inelastic neutron scattering (INS). It was found that the actual structure of the gamma phase is orthorhombic, space group Cccm, rather than tetragonal as previously believed. The one-phonon deuterium optical band in the INS spectrum was observed at an energy transfer of 107 meV (with the main feature at 103.4 meV), which is higher than the deuterium vibrational energies for all other phases of the Zr-D system. Distinct features were also observed in the INS spectrum below the free multiphonon bands, which were explained as the bound multiphonon states.

Thermally stable hydrogen compounds obtained under high pressure on the basis of carbon nanotubes and nanofibers

Compounds containing 6.3–6.5 wt % H and thermally stable in vacuum up to 500°C were obtained by annealing graphite nanofibers and single-walled carbon nanotubes in hydrogen atmosphere under a pressure of 9 GPa at temperatures up to 45°C. A change in the X-ray diffraction patterns indicates that the crystal lattice of graphite nanofibers swells upon hydrogenation and that the structure is recovered after the removal of hydrogen. It was established by IR spectroscopy that hydrogenation enhances light transmission by nanomaterials in the energy range studied (400–5000 cm−1) and results in the appearance of absorption bands at 2860–2920 cm−1 that are characteristic of the C–H stretching vibrations. The removal of about 40% of hydrogen absorbed under pressure fully suppresses the C–H vibrational peaks. The experimental results are evidence of two hydrogen states in the materials at room temperature; a noticeable portion of hydrogen forms C–H bonds, but the most of the hydrogen is situated between the graphene layers or inside the nanotubes.

A real-time neutron diffraction study of phase transitions in the Ti-D system after high-pressure treatment

Phase transitions in TiDapproximately 0.75 subjected to high-pressure treatment were investigated by simultaneous real-time measurements of neutron diffraction and small-angle neutron scattering. The neutron spectra were taken on heating the samples in the temperature ranges 100 to 300 K and 300 to 760 K followed by cooling to 430 K. A sequence of structural transitions was observed, which involves seven different phases and intermediate states with the hexagonal close-packed, face-centred cubic, face-centered orthorhombic or body-centred cubic metal sublattices and hydrogen atoms distributed on octahedral or ordered/disordered tetrahedral interstices.

Displacive ordering in the hydrogen sublattice of yttrium trihydride

Powder samples of YH3 and YD3 have been studied by neutron diffraction (ND) with a much higher statistical accuracy than obtained previously. The profile analysis of the obtained ND patterns confirmed the high-symmetry HoH3-type structure of YH3 and ruled out the ‘broken symmetry’ structures proposed recently to explain the insulating properties and lattice dynamics of this compound. At the same time, it was demonstrated that the HoH3type structure is only the structure of the mean lattice of YH3 .L argestatic displacements of H atoms from the symmetrical positions in this structure do occur, and ordering of these displacements on a short-range scale can settle the controversies between the crystal structure and physical properties of YH3.

Neutron spectroscopy of fullerite hydrogenated under high pressures

A new hydrofullerite was synthesized when the C 60 fullerite was treated under a hydrogen gas pressure of 30 kbar at 620 K for 24 h and quenched. The inelastic neutron scattering spectra of the as-prepared sample and that after annealing at 300 K showed that the as-prepared hydrofullerite consisted of C 60 H x molecules and interstitially dissolved molecular hydrogen. Both spectra exhibited peaks at 13 meV characteristic of polymeric fullerites. ( 1999 Elsevier Science B.V. All rights reserved.

Inelastic neutron scattering study of ordered gamma -ZrH

Lattice dynamics of the ordered gamma -ZrH phase was studied by inelastic neutron scattering (INS). It was found that the hydrogen optical peak in the INS spectrum had three maxima at energy transfers of 141.5, 148.7 and 156.3 meV. The peak was accurately described using the Born-von Karman model. Anharmonicity of hydrogen vibrations was evident in the high-energy range of the spectrum from a strong sharp peak at E=269.7 meV and broader features below the bands of free-multiphonon scattering. These anharmonic phenomena were attributed to the bound multiphonon states (biphonon, triphonon, tetraphonon and their combinations), and the values of the binding energies of biphonons and triphonons were obtained from the experimental data.

Photoluminescence of solid C60 polymerized under high pressure

Abstract Photoluminescence (PL) spectra were measured on the C 60 polymeric phase prepared from a single crystal and from a microcrystalline powder treated at pressures to 15 kbar and temperatures to 600 K. It was found that the high-pressure treatment resulted in a shift of the spectral intensity distribution to lower energies compared to the well-known spectrum of pristine C 60 . A set of new lines was observed. The PL spectrum of the high-pressure phase exhibited a distinct structure contrary to that of photopolymerized C 60 . The PL intensity of the high-pressure phase showed a non-monotomic temperature dependence with a slight minimumum around 150 K.