P.A. Georgiev

Hydrogen site occupancies in single-walled carbon nanotubes studied by inelastic neutron scattering

Neutron inelastic scattering spectra from high quality single-wall carbon nanotubes (SWNTs), progressively dosed with hydrogen, have been measured with high resolution at different temperatures in the vicinity of 20 K. The spectra consist of two parts. Firstly, a relatively sharp complex peak, due to scattering from translationally bound molecules undergoing rotational transitions, is observed at around 14.5 meV. Secondly, there is a series of broad features at higher energies originating from roto-vibrational transitions corresponding to J = 0 to 1 rotational change plus n = 0 to n = 1, 2, etc molecular centre-of-mass vibrational transitions, as well as from molecule centre-of-mass recoil. The structure of the complex sharp peak suggests that the molecular hydrogen is adsorbed on at least two different adsorption sites on the surfaces of the nanotube bundles.

An in situ neutron time-of-flight diffraction study of LaMM(NiCoAlMn)5-x battery electrode materials and their deuterides, for x=0 and x=0.2

The structural properties of two mechanically activated commercial LaNi5 type battery materials and their deuterides have been investigated by means of in situ neutron powder diffraction analysis. A discussion of the hysteresis between the absorption and desorption isotherms is given. Using standard Rietveld refinement procedures, information on the variation of the deuterium site occupancy, the lattice symmetry and the cell volume are also presented. In particular, we report on the variation of line-broadening with concentration as well as on the complex time-dependent changes in the lattice parameters and the line-broadening following a step change in the deuterium pressure. We then show that these relatively novel data provide valuable information on the rather different phase transition processes observed for the two materials and offer an explanation for the superior kinetics of the AB4.8 alloy.

Magnetic properties of the YCo3–H system

The YCO 3 -H system is an interesting system, which shows a dramatic influence of hydrogen absorption on its magnetic properties. The β-hydride phase has been divided into β 1 and β 2 phases originally due to their different magnetic properties. Our measurement of the absorption isotherm at room temperature, however, shows clearly that the β phase is actually separated into two phases. Thus a new hydride phase has been identified. Magnetisation measurements have also been made using a VSM. The results show that the β 1 phase is most likely to be paramagnetic. We also observe that the β 2 phase seems to have two Curie temperatures. Because there are three types of Co atoms in the YCo 3 structure, we would infer that the magnetic ordering of the different Co atoms takes place at different temperatures in this phase.