Marie Vennström

Structure of Ti2P solved by three-dimensional electron diffraction data collected with the precession technique and high-resolution electron microscopy

The crystal structure of Ti(2)P has been analysed using electron diffraction and high-resolution electron-microscopy techniques. A new unit cell was found, the compound is hexagonal with a = 19.969 (1) and c = 3.4589 (1) A. The structure was first solved in space group P-62m in projection using direct methods on electron diffraction data from the [001] zone axis. A three-dimensional solution was obtained using again direct methods but on a three-dimensional set of electron diffraction data recorded with the precession technique. Ti(2)P is a distorted Fe(2)P structure and, based on high-resolution images, it is possible to explain that the tripling of the unit cell is due to the ordering of P vacancies that reduces the symmetry to P-6.

Crystal structural properties of Ti3SnD

Abstract Ti 3 Sn crystallises in hexagonal Ni 3 Sn type structures. Upon deuteration a primary interstitial solid solution of deuterium in Ti 3 Sn has been identified. At higher deuterium concentrations a cubic hydride phase is formed with the limiting composition Ti 3 SnD. The structural properties of these phases have been refined from neutron powder diffraction intensities using the Rietveld method. The crystal structure of Ti 3 SnD has been confirmed to crystallize in the CaTiO 3 type structure, space group Pm 3 m , with the unit cell parameter a =4.1769(4) A. The deuterium atoms occupy Ti 6 octahedral voids in the cubic structure to 95.7(6)% and 72(6)% in the hexagonal.

Hydrogen absorption in Nb4CoSi and Nb4NiSi

Abstract Nb 4 CoSi and Nb 4 NiSi, crystallising with the Al 2 Cu-type structure, space group I 4/ mcm , absorb considerable amounts of deuterium at room temperature and 90-kPa deuterium pressure. The deuterium contents were determined to be Nb 4 CoSiD 2.5 and Nb 4 NiSiD 2.7 from refinements of neutron powder diffraction profiles using the Rietveld method. Two crystallographic sites, 4 b and 16 l , are occupied by deuterium to 78.2(6)% and 12.2(3)% in Nb 4 CoSiD 2.5 and 63.6(8)% and 18.6(5)% in Nb 4 NiSiD 2.7 . Each deuterium atom coordinates four niobium atoms in a tetrahedral arrangement. The crystal structures of Nb 4 CoSiD 2.5 and Nb 4 NiSiD 2.7 are compared to some hydrogen absorbing binary compounds with the Al 2 Cu-type structure.

Neutron Powder Diffraction Investigation of Pd2.7Ni0.3P0.94

Pd3P, which crystallises in the cementite, Fe3C-type structure, forms a solid solution with nickel. The crystal structure contains two crystallographically different palladium sites (8d and 4c). Refinements of neutron powder diffraction intensities using the Rietveld method show that all nickel atoms occupy the eight-fold position. The unit cell parameters were refined to a=5.7812(4) Å, b=7.4756(6) Å and c=5.1376(4) Å, for Pd2.7Ni0.3P0.94.

Comparison of the dynamics of hydrogen and deuterium dissolved in crystalline Pd9Si2 and Pd3P0.8

Abstract The bonding potentials of hydrogen and deuterium dissolved in the crystalline alloys Pd 9 Si 2 and Pd 3 P 0.8 have been studied by neutron scattering techniques. Neutron powder diffraction verifies that, in both alloys, the principal type of interstitial absorption site is the quadrilateral base of a Pd-defined pyramid situated on the face of an empty triangular prism. The neutron vibrational spectroscopy results indicate that, although the H and D vibrational energies parallel to the Pd pyramidal base appear to be similar for both alloys, the H and D vibrational energies perpendicular to the Pd pyramidal base for Pd 9 Si 2 are ≈15% softer than the corresponding energies for Pd 3 P 0.8 . Both neutron vibrational spectroscopy and quasielastic neutron scattering show that hydrogen hopping between the two pyramidal absorption sites associated with different faces of the same prism is much more rapid in Pd 9 Si 2 than in Pd 3 P 0.8 . This may be directly attributable to the observed softer potential along the hopping trajectory (i.e. perpendicular to the Pd pyramidal base) for the interstitial site in Pd 9 Si 2 compared to that in Pd 3 P 0.8 .