Hendrik W. Brinks

Neutron diffraction structure determination of NaAlD4

Abstract The structure of NaAlD4 has been determined from Rietveld-type refinements of powder neutron diffraction data at 8 and 295 K. The space group is I41/a with a=501.19(1) and c=1131.47(5) pm at 295 K. The Na atoms are surrounded by eight D atoms from eight different [AlD4]− tetrahedra in the geometry of a distorted square antiprism. The two different Na–D distances are nearly equal: 240.3(2) and 240.5(2) pm at 8 K and 243.1(2) and 243.9(2) pm at 295 K. The Al–D distance is 162.7(2) and 162.6(2) pm at 8 and 295 K, respectively.

The crystal structure of Zr2NiD4.5.

The crystal structure of Zr2NiD4.5 has been determined by a combination of synchrotron radiation powder X-ray diffraction, electron diffraction and powder neutron diffraction data. Deuterium ordering results in a triclinic supercell given by asuper=6.81560 (7), bsuper=8.85137 (9), csuper=8.88007 (10) A, alphasuper=79.8337 (8), betasuper=90.0987 (9), gammasuper=90.3634 (9) degrees, which relates to the non-super unit cell as asuper=-a, bsuper=-b-c, csuper=-b+c. The centrosymmetric and fully ordered deuterium sublattice was determined by simulated annealing and Rietveld refinement. Deuterium was found to occupy three types of tetrahedral sites: two that are coordinated by four Zr atoms and one that is coordinated by three Zr atoms and one Ni atom. All D-D distances are longer than 2 A. The feasibility of the crystal structure was supported by density functional theory calculations.

Determination of deuterium site occupation in Zr4Pd2OD4.5

Abstract Powder neutron diffraction analysis has been used to determine hydrogen site occupation at room temperature in the lattice of the oxygen-stabilized Zr 4 Pd 2 O phase. For the composition Zr 4 Pd 2 OD 4.5 it was established that only two types of interstices, designated as D7 and D2, were occupied. Hydrogen in the D7 site is octahedrally surrounded by 6Zr. This site is nearly filled. In the D2 site hydrogen is tetrahedrally co-ordinated to 3Zr and Pd and is 1/3 filled. The distribution of hydrogen on the D2 sites is random.

Electron microscopy studies of a TbNiAl compound processed by the HDDR route

Abstract A TbNiAl compound processed by the hydrogenation disproportionation desorption recombination route has been studied using a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM backscattered electron (BSE) images showed fine scale composition variations associated with the disproportionation stage while in the recombination stage no structure was visible. TEM examination showed nanocrystalline regions in the disproportionation stage. Selected area diffraction (SAD) showed the existence of two phases TbD 2.2 and NiAl in the disproportionation stage and single phase TbNiAl in the recombination stage and the measured d -spacings correlate well with the literature. The distribution of the phases in the disproportionation stage was studied by high-resolution TEM.