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Abstract: LaPtIn was attempted hydrogenated at a hydrogen pressure of 182bar and temperatures from room temperature to 673K. The crystal structure of the resulting LaPtInH0.53 hydride was determined from powder neutron diffraction data. The structure was indexed on an expanded LaPtIn intermetallic unit cell with space group and dimensions a =7.8229(2)Å and c =4.1647(2)Å. Hydrogen occupies tetrahedral 4h sites in such a way that tetrahedral voids sharing a common face are not simultaneously populated. The result could not support previous density-functional theory calculations regarding the hydrogen absorption capacity of LaPtIn [P. Ravindran, P. Vajeeston, R. Vidya, A. Kjekshus, H. Fjellvåg, Phys. Rev. Lett. 89 (2002) 106403]. [Copyright &y& Elsevier]

Abstract: The twice hydrogen (H) cycled planetary milled (PM) NaAlH4 + xTMCl n (transition metal (TM)=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Pd, Pt; 2< n <4) and cryo milled (CM) NaAlH4 + xTMCl n (TM=Ti, V, Cr, Fe, Ni; 2< n <3) systems (x <0.1) have been studied by high resolution synchrotron X-ray diffraction. Face centred cubic (fcc) A1 crystalline (c-) Al1−x TM x (x <0.25) solid solutions are evident in PM samples for Sc, Ti, V, Cr, Mn, Zr and Pd while PM samples of Cu, Ni, Pd and Pt display mostly ordered and numerous crystalline Al1−x TM x phases. Very broad reflections in the 2Å d-spacing region for Cr, Mn, Co, and Pd are identified as partially ordered body centred cubic (bcc) A2 and B2 Al1−x TM x type structures. The amorphous (a-) Al1−x V x phase observed in the H cycled PM NaAlH4 + xVCl3 system ranges in composition from a-Al90V10 (x =0.02) up to a-Al72V28 (x =0.1). Across the TM series, the Al1−x TM x particle size ranges as Sc-V 4-25nm, Cr, Mn, Co <5nm, Fe 5–15nm, Ni, Cu <50nm. A highly ‘compressed’ NaAlH4 phase is observed in the H cycled PM NaAlH4 +0.1ScCl3 system, with unit cell dimensions of a =4.9995(2)Å and c =11.2893(1)Å, compared to the average dimensions of ‘normal’ NaAlH4 across the TM and rare earth (RE) series with a =5.0228(1)Å and c =11.3516(1)Å. [Copyright &y& Elsevier]

Abstract: By means of in situ synchrotron radiation powder X-ray diffraction, powder neutron diffraction, attenuated total reflectance infrared spectroscopy, differential scanning calorimetry and the Sieverts techniques we have investigated how anion substitution in the LiBH4–LiBr system leads to changes in the structural, physical, chemical and hydrogen storage properties of this material. Mechano-chemical treatment facilitates formation of a hexagonal solid solution h-Li(BH4)1−xBrx whereas heating at elevated temperatures, i.e. T > 112 °C appears to allow full solubility in the system LiBH4−LiBr. The first step in the anion substitution process may be dissolution of small amounts of LiBH4 in α-LiBr deduced from observation of a hexagonal solid solution with unit cell volume similar to β-LiBr for a hand-mixed sample. The solid solution, Li(BH4)1−xBrx, is isostructural to the hexagonal high temperature polymorph of LiBH4. This solid solution melts at a significantly higher temperature depending on the composition as compared to h-LiBH4. Furthermore, a new hexalithium borate tribromide, Li6(BO3)Br3 was discovered and structurally characterized. [Copyright &y& Elsevier]

Abstract: The NaH + Al + 0.02CeCl3 system has been studied by high-resolution X-ray synchrotron diffraction and transmission electron microscopy (TEM), after planetary milling under hydrogen and hydrogen (H) cycling. Isothermal absorption kinetics were determined at 150 °C, and compared with the NaH + Al + 0.02TiCl3 system, indicating that CeCl3 and TiCl3 are equally effective additives, with CeCl3 preferred on the basis of hydrogen storage capacity. After milling, AlCe contains 100% of the Ce. After the first H absorption, we observe two Al1−xCex phases. The first, AlCe, contains ca. 60% of the originally added Ce atoms. The AlCe phase observed after milling and H cycling is chemically disordered, with complete exchange between the Al and Ce sublattices occurring, yielding zero intensity in ordering reflections such as (100). In the absorbed state after H cycling, the remaining 40% of Ce atoms are contained in a cubic Al1−xCex phase not previously observed in the Al-Ce phase diagram. Indexing yields a primitive cubic unit cell of dimension 7.7111 Å, in space group P23. Lineshape analysis indicates the AlCe and unknown cubic Al1−xCex phases are ca. 35 nm and 30 nm in dimension respectively. High resolution TEM imaging confirms that both Al1−xCex phases are embedded on the NaAlH4 surface, and localised energy dispersive X-ray spectroscopy (EDS) indicates a ca. 2:1 Al:Ce ratio for the unknown cubic Al1−xCex phase. [Copyright &y& Elsevier]

Abstract: The twice-hydrogen-cycled NaAlH4 + xTiCl3 (x <0.15) system has been studied by high-resolution X-ray synchrotron diffraction and transmission electron microscopy. Intense low d-spacing shoulders are formed on Al reflections, indicating the formation of a face-centred cubic Al85Ti15 solid solution of unit cell dimension 4.0356Å. The Al85Ti15 solid solution is found as isolated 4–25nm nanocrystallites on the NaAlH4 surface. The Al85Ti15 phase is highly 〈110〉{111} edge dislocated to ∼6×1016 m−2. Local energy-dispersive spectroscopy shows an Al:Ti ratio consistent with an Al85Ti15 composition, confirming an extended solubility of Ti in Al. Structural analysis indicates a quenched L12 superlattice obtained by Al and Ti sublattice swapping, yielding an equivalent A1 model to describe the Al85Ti15 crystal structure. [Copyright &y& Elsevier]

Abstract: The mixed alanate K2NaAlH6 has been synthesised by ball-milling a mixture of KH and NaAlH4 and subsequent annealing at 150°C under a stabilizing hydrogen pressure. It takes a cubic ordered perovskite-type structure (space group , a =8.118(1)Å) where the ideal octahedral AlH6 3− units form a cubic close-packed structure with K+ in all tetrahedral sites and Na+ in all octahedral sites. K2NaAlH6 with 1mol% TiF3 decompose quickly and reversibly with a flat plateau. Pressure-composition isotherms have been measured at five temperatures in the range 280–325°C. The decomposition enthalpy and entropy were determined to 98(2)kJ/mol H2 and 150(4)J/(KmolH2) from the van’t Hoff equation. [Copyright &y& Elsevier]

The intrinsic ageing of the CaNi5Dx system has been studied at 80 °C and 9 bar over a period of 13 days. The system displays a distinct two-phase mixture of the intermediate α′ and β phases, whose phase proportions approach 40 and 50 wt.%, respectively at the end of the ageing period. The change in proportion of each intermediate phase and free fcc Ni suggests two periods of Ni depletion. The amount of free Ni in the system is doubled through the ageing period. The orthorhombic symmetry of the α′ and β phase is preserved, albeit with a strong depletion of three of the four Ni positions from the β phase during the second half of the ageing period. That one half of the hexagonally equivalent 2c Ni position does not release Ni indicates that low symmetry geometrical ordering in orthorhombic symmetry is responsible for the rapid loss of recoverable hydrogen capacity in this system. [Copyright &y& Elsevier]

The recent powder neutron diffraction study of the crystal structure of LaNiInD1.22 [J. Alloys Comp. 330–322 (2002) 132] concluded on the formation of a D…D pair with an unusually short interatomic distance of 1.63 A˚. Hydrogen atoms in LaNiInD1.22 occupy a single crystallographic site and are coordinated by face-sharing La3Ni tetrahedra (92% occupancy). PCT measurements show that hydrogen storage capacity of LaNiIn, 1.63 at.H/formula unit, exceeds the limit of 1.33 at.H/LaNiIn when the La3Ni sites are completely occupied. In the present work, in situ powder neutron diffraction data were collected under D2 pressure of 4.6 bar in order to study the deuteride with a maximum D content in the metal matrix. In the hexagonal structure of LaNiInD1.63 (space group P6¯2m; a=7.3874(4); c=4.6816(2) A˚) Rietveld refinements showed that deuterium atoms occupy 36% of the available distorted La3NiIn2 octahedra, in addition to the 96% filled La3Ni sites. The structure of LaNiInD1.63 represents the first example of a deuteride containing direct In–D bonds (2.346(2) A˚). H bonding to the La3NiIn2 sites is rather weak and a desorption from these sites takes place at room temperature and hydrogen pressures below 1 bar. [Copyright &y& Elsevier]

Abstract: The hydrogen absorption ability of the non-absorbing Al-rich ZrAl2 compound was examined after reducing its particles-size to the nanometer regime. The hydrogen abstinence of bulk ZrAl2 has been previously related to its excessive elastic shear stiffening. The particle size of ZrAl2 was reduced by attrition milling and cryomilling. The minimal average particle size was estimated from powder X-ray diffraction analysis to be in the range of 10–20nm. The hydrogen absorption of the milled compounds was measured in different hydrogenation systems at hydrogen pressures between ∼6MPa and ∼2GPa. In all the cases the hydrogen absorption was negligible. In addition, there was a reduction of the hydrogen absorption capacity of nanosized Zr(Al0.5Co0.5)2 as compared to the corresponding bulk compound at the same conditions. We suggest, in view of our and other results, that no significant improvement of the thermodynamics (unlike the kinetics) of the hydrogen absorption can be achieved via the nanoparticle avenue. [Copyright &y& Elsevier]