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We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Ca(BD4)2 shows a variety of structures depending on the synthesis and temperature of the samples. An unknown tetragonal crystal of Ca(BD4)2, the beta phase has been solved from diffraction data measured at 480 K on a sample synthesized by solid-gas mechanochemical reaction by using MgB2 as starting material. Above 400 K, this sample has the particularity to be almost completely into the beta phase of Ca(BD4)2. Seven tetragonal structure candidates gave similar fit of the experimental data. However, combined experimental and ab initio calculations have shown that the best description of the structure is with the space group P4(2)/m based on appropriate size/geometry of the (BD4)tetrahedra, the lowest calculated formation energy, and real positive vibrational energy, indicating a stable structure. At room temperature, this sample consists mainly of the previously reported alpha phase with space group Fddd. In the diffraction data, we have identified weak peaks of a hitherto unsolved structure of an orthorombic gamma phase of Ca(BD4)2. To properly fit the diffraction data used to solve and refine the structure of the beta phase, a preliminary structural model of the gamma phase was used. A second set of diffraction data on a sample synthesized by wet chemical method, where the gamma phase is present in significant amount, allowed us to index this phase and determine the preliminary model with space group Pbca. Ab initio calculations provide formation energies of the alpha phase and beta phase of the same order of magnitude (delta H < or = 0.15 eV). This indicates the possibility of coexistence of these phases at the same thermodynamical conditions.

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) Å, αsuper = 79.8337 (8), βsuper = 90.0987 (9), γsuper = 90.3634 (9)°, 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 Å. The feasibility of the crystal structure was supported by density functional theory calculations. [ABSTRACT FROM AUTHOR]

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) Å, αsuper = 79.8337 (8), βsuper = 90.0987 (9), γsuper = 90.3634 (9)°, 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 Å. The feasibility of the crystal structure was supported by density functional theory calculations. [ABSTRACT FROM AUTHOR]

Abstract: The crystal structure of LiZn2(BH4)5 is studied in detail using a combination of powder neutron diffraction (PND), Raman spectroscopy, and 11B MAS NMR spectroscopy on LiZn2(BH4)5 and LiZn2(11BD4)5. The aim is to obtain detailed structural knowledge of the first interpenetrated framework hydride compound, LiZn2(BD4)5 which consists of doubly interpenetrated 3D frameworks built from dinuclear complex ions [Zn2(BD4)5]− and lithium ions. The positions of the deuterium atoms are determined using Rietveld refinement of the PND data and the orientation of one of the four independent BD4 − groups is revised. The current data reveal that the structure of [Zn2(BD4)5]− is more regular than previously reported, as are also the coordinations around the Zn and Li atoms. Both Zn and Li atoms are found to coordinate to the BD4 − units via the tetrahedral edges. Some distortion of the angles within the BD4 units is observed, relative to the expected angles of 109.4 for the ideal tetrahedral coordination. Raman spectroscopy confirms bending and stretching modes from the expected terminal and bridging bidentate BH4ˉ and BD4ˉ units. The 11B MAS NMR spectrum of the satellite transitions resolves two distinct manifolds of spinning sidebands, which allows estimation of the 11B quadrupole coupling parameters and isotropic chemical shifts for the four distinct 11B sites of [Zn2(BD4)5]−. These parameters agree favorably well with the isotropic triple-quantum shifts, observed in an 11B MQMAS NMR experiment. The present results may aid in the development and understanding of new borohydride materials for applications as fast ion conductors or as materials for hydrogen storage. [Copyright &y& Elsevier]