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La 2 MgNi 9 -related alloys are superior metal hydride battery anodes as compared to the commercial AB 5 alloys. Nd-substituted La 2- y Nd y MgNi 9 intermetallics are of particular interest because of increased diffusion rate of hydrogen and thus improved performance at high discharge currents. The present work presents in operando characterization of the LaNdMgNi 9 intermetallic as anode for the nickel metal hydride (Ni- M H) battery. We have studied the structural evolution of LaNdMgNi 9 during its charge and discharge using in situ neutron powder diffraction. The work included experiments using deuterium gas and electrochemical charge-discharge measurements. The alloy exhibited a high electrochemical discharge capacity (373 mAh/g) which is 20% higher than the AB 5 type alloys. A saturated β -deuteride synthesized by solid-gas reaction at P D2 = 1.6 MPa contained 12.9 deuterium atoms per formula unit (D/f.u.) which resulted in a volume expansion of 26.1%. During the electrochemical charging, the volume expansion (23.4%) and D-contents were found to be slightly reduced. The reversible electrochemical cycling is performed through the formation of a two-phase mixture of the α -solid solution and β -hydride phases. Nd substitution contributes to the high-rate dischargeability, while maintaining a good cyclic stability. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the anode electrode on cycling. A mathematical model for the impedance response of a porous electrode was utilized. The EIS showed a decreased hydrogen transport rate during the long-term cycling, which indicated a corresponding slowing down of the electrochemical processes at the surface of the metal hydride anode. [ABSTRACT FROM AUTHOR]

Abstract: Two new ternary intermetallic compounds, CeMgCo4 (C15b pseudo-Laves phase, MgCu4Sn type) and Ce2MgCo9 (substitution derivative of PuNi3 type) were synthesized by mechanical alloying method. The structural and hydrogenation properties of these compounds were studied by X-ray diffraction and Pressure–Composition–Temperature measurements. Both compounds absorb hydrogen at room temperature and pressures below 10MPa forming hydrides with maximum compositions CeMgCo4H6 and Ce2MgCo9H12. Single plateau behavior was observed in P–C isotherm during hydrogen absorption/desorption by Ce2MgCo9 alloy. The CeMgCo4–H2 system is characterized by the presence of two absorption/desorption plateaus corresponding to formation of β-CeMgCo4H4 and γ-CeMgCo4H6 hydride phases. The structure of β-hydride CeMgCo4H(D)4 was determined from X-ray and neutron powder diffraction data. In this structure initial cubic symmetry of CeMgCo4 is preserved and hydrogen atoms fill only one type of interstitial sites, triangular MgCo2 faces. These positions are occupied by 70% and form octahedron around Mg atom with Mg–D bond distances 1.84Å. [Copyright &y& Elsevier]

Abstract: A novel low-temperature hydride, Mg3MnNi2D3−x with filled Ti2Ni-type structure has been synthesised and its crystal structure has been studied in detail by powder neutron diffraction. Refinement of the structures of β-Mg3MnNi2D1.83 and α-Mg3MnNi2D0.23 deuteride phases showed that D atoms partially fill 16d Mg6 octahedral and 32e Mg3Ni tetrahedral interstices in the cubic metal matrix (sp.gr. ). The β-hydride was found to be rather unstable, during storage in air it transforms into α-hydride. [Copyright &y& Elsevier]

Abstract: New ternary Mg–Mn–Ni alloys synthesised by high energy ball milling have been studied as hydrogen storage materials. A new Mg3MnNi2 ternary intermetallic compound of the Ti2Ni type has been identified, its structure was studied by neutron diffraction. It has been shown that in the Mg–Mn–Ni system this intermetallic coexists with Mg, forming two-phase Mg–Mg3MnNi2 alloys. The Mg3MnNi2 compound reversibly absorbs about 1 wt.% of hydrogen already at room temperature and forms interstitial type Mg3MnNi2H∼3 hydride. Substantially higher hydrogenation capacity has been observed in Mg–Mg3MnNi2 alloys with high Mg content, e.g. 5.4 wt.% for the Mg88Mn4Ni8 alloy at 250–350 °C. Hydrogen absorption–desorption kinetics of these alloys are drastically improved compared to undoped magnesium due to catalytic effect of the Mg3MnNi2 phase. [Copyright &y& Elsevier]

Abstract: The present work is focused on studies of the influence of magnesium on the hydrogenation behaviour of the (La,Mg)2Ni7 alloys. Substitution of La in La2Ni7 by Mg to form La1.5Mg0.5Ni7 preserves the initial Ce2Ni7 type of the hexagonal P63/mmc structure and leads to contraction of the unit cell. The system La1.5Mg0.5Ni7–H2 (D2) was studied using in situ synchrotron X-ray and neutron powder diffraction in H2/D2 gas and pressure–composition–temperature measurements. La replacement by Mg was found to proceed in an ordered way, only within the Laves-type parts of the hybrid crystal structure, yielding formation of LaMgNi4 slabs with statistic and equal occupation of one site by La and Mg atoms. Mg alters structural features of the hydrogenation process. Instead of a strong unilateral anisotropic expansion which takes place on hydrogenation of La2Ni7, the unit cell of La1.5Mg0.5Ni7D9.1 is formed by nearly equal hydrogen-induced expansions proceeding in the basal plane (Δa/a=7.37%) and along [001] (Δc/c=9.67%). In contrast with La2Ni7D6.5 where only LaNi2 layers absorb hydrogen atoms, in La1.5Mg0.5Ni7D9.1 both LaNi5 and LaMgNi4 layers become occupied. Nine types of sites were found to be filled by D in total, including tetrahedral (La,Mg)2Ni2, (La,Mg)Ni3, Ni4, tetragonal pyramidal La2Ni3 and trigonal bipyramidal (La,Mg)3Ni2 interstices. The hydrogen sublattice around the La/Mg site shows formation of two co-ordination spheres of D atoms: an octahedron MgD6 and a 16-vertex polyhedron LaD16 around La. The interatomic distances are in the following ranges: La–D (2.28–2.71), Mg–D (2.02–2.08), Ni–D (1.48–1.86Å). All D–D distances exceed 1.9Å. Thermodynamic PCT studies yielded the following values for the ΔH and ΔS of hydrogenation/decomposition; ΔH H=−15.7±0.9kJ(molH)−1 and ΔS H=−46.0±3.7J(KmolH)−1 for H2 absorption, and ΔH H=16.8±0.4kJ(molH)−1 and ΔS H=48.1±1.5J(KmolH)−1 for H2 desorption. [Copyright &y& Elsevier]

Abstract: ‘Hybrid’ RNi3 (R=rare earth metal) crystal structures are built of the slabs of simpler types, CaCu5 and MgZn2. Different affinities of these slabs to hydrogen result in unusual “anisotropic” expansion of the RNi3 and R2Ni7 (R=La, Ce) structures upon hydrogenation. This work focuses on studies of the hydrogenation behaviour of LaNi3 and on the properties of the hydrides of the modified by Mg and Mn La–Ni alloys. The crystal structure of LaNi3D2.8 and the crystal structure and hydrogen storage behaviours of the La1.5Mg0.5Ni7 and La(Ni1−x Mn x )3 (x =0; 0.067; 0.133; 0.2; 0.267; 0.3; 0.333; 0.4) alloys were in focus. The deuteration of LaNi3 with PuNi3 type of structure leads to the formation of LaNi3D2.8 and is accompanied by a deformation of the metal matrix causing a change of the initial rhombohedral symmetry (space group ) to a monoclinic one (space group C2/m; a =8.6408(7)Å, b =4.9281(4)Å, c =32.774(3)Å; β =90.850(8)°; V =1395.5(2)Å3). Similar to the earlier studied CeNi3D2.8, preferential occupation by deuterium atoms of the AB2 layers takes place, leading to the “anisotropic” expansion of the unit cell along [001] (Δc/c =30.6%). 14 occupied D crystallographic sites have 4 chemically different types of metal-atom surroundings, including Ni4 (2), La2Ni2 (2), La3Ni (6), and La3Ni3 (4). Modification of the La–Ni alloys by magnesium and manganese leads to the formation of intermetallic compounds crystallising with the PuNi3, CeNi3, and Ce2Ni7-type structures. An ordered substitution of La by Mg in the MgZn2-type slabs was observed, causing a complete alteration of the hydrogenation behaviour of the original LaNi3 alloy. La1.5Mg0.5Ni7D 9 isotropically expands upon its formation and leads to a substantial increase of the stability against hydrogenation-induced amorphisation. On the other hand, replacement of Ni by Mn leads to the change in crystal-structure type from PuNi3 to CeNi3 in the LaNi3−x Mn x alloys (x >0.1). An ordered substitution of Ni by Mn proceeds inside the RNi5 slabs only. This decreases the stability of the initial alloy against amorphisation on hydrogenation. [Copyright &y& Elsevier]

Abstract: A new intermetallic deuteride Ce2Ni7D4.7 with an anomalous volume expansion has been studied. Its structure was solved on the basis of in situ neutron diffraction data. Expansion proceeds along the c-axis and within the CeNi2 slabs only. All D atoms are located inside these slabs and on the border between CeNi2 and CeNi5. Ordering of D atoms in the bulk of CeNi2 is accompanied by substantial deformation of these slabs thus lowering the hexagonal symmetry to orthorhombic [space group Pmcn (No. 62); a=4.9251(3)Å, b=8.4933(4)Å, c=29.773(1)Å]. Inside the CeNi2 layer the hydrogen sublattice is completely ordered; all D–D distances exceed 2.0Å. Local coordination of Ni by D inside the CeNi2 blocks is of “open”, saddle-like type. Hydrogen ordering is mainly determined by Ce–H and H–H interactions. The pressure–composition–temperature measurements yielded the following thermodynamic parameters of the formation of the hydride: ΔH=−22.4kJ/molH, ΔS=−59.9J/(KmolH). [Copyright &y& Elsevier]

Abstract: The crystal and magnetic structure of TbNiSnD has been studied by neutron powder diffraction. The deuteride crystallizes with the filled TiNiSi type structure (sp. gr. Pnma; a=7.0354(1); b=4.20662(9); c=8.1808(2)Å at 293K; a=7.008(1); b=4.1954(6); c=8.153(1)Å at 2K) and is canted ferromagnetic below 10K. The deuterium atoms occupy the tetrahedral Tb3Ni sites. The Tb atoms carry a magnetic moment of 6.6(1) μ B /Tb. They order antiferromagnetically along the a-axis and ferromagnetically along the c-axis. No significant magnetic moment on the Ni atoms has been observed by neutron diffraction. Insertion of deuterium in TbNiSn induces both a change of the magnetic structure and a reduction of the Tb magnitude of the magnetic moment. [Copyright &y& Elsevier]

Abstract: The crystal structure of NdNiInD1.2 contains D–D pairs with the shortest known separation of 1.56 Å. This work was aimed on studies of the factors influencing the formation and the length of such a pair. We have studied the NdNiIn-based alloys, in which Ni or In are partially substituted by the chemically related elements, Cu or Al, respectively. Three equiatomic intermetallics, NdNiIn, NdCuIn and NdNiAl, are isostructural and crystallise with the ZrNiAl type of structure. In the NdNi1−x Cu x In (; 0.02; 0.05; 0.25; 0.50; 0.75 and 1.00) quaternary system a complete solid solubility range has been found. In contrast, in the Al-containing NdNiIn1−x Al x alloys the range of a solid solution is limited to the region NdNiIn–NdNiIn0.75Al0.25. The substitutions result in regular changes in V, a, c and of the hexagonal unit cells. Small substitutions by Cu and Al () do not lead to significant changes in H content and types of the crystal structures formed (PND data). However, a decrease in the stability of the hydrides is observed. In NdNi1−x Cu x In, Cu has a strong preference for the occupation of the CuIn6 trigonal prisms. An increase of the Cu content is accompanied by a decrease of the D/Nd(Ni1−x Cu x )In ratio and a distinct growth of the distance between Ni(Cu) and D (from 1.51 to 1.84 Å). pairing is very sensitive to the content of both Al and Cu. When the level of substitution exceeds , H pairing becomes unstable and H atoms favour other types of ordering in the metal sublattice. [Copyright &y& Elsevier]

It is shown that the oxygen-stabilised compounds Zr3Fe(Co)Ox (x = 0–1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with filled Re3B type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.7 H/f.u. for Zr3Fe down to 5.35 H/f.u. for Zr3FeO1.0 and from 6.9 H/f.u. for Zr3Co down to 5.3 H/f.u. for Zr3CoO1.0. A small change of the unit cell volumes for the Zr3Fe(Co)Ox parent compounds and a substantial increase of these parameters for the corresponding saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, ΔV/at. H, increases from 2.25 Å3 for Zr3FeH6.7 up to 3.38 Å3 for Zr3FeO1.0H5.35 and from 2.08 Å3 for Zr3CoH6.9 up to 3.25 Å3 for Zr3CoO1.0H5.3. Rietveld refinement using neutron powder diffraction data for Zr3FeO0.4D6.25 showed a distribution of deuterium atoms and a redistribution of oxygen atoms from octahedral to tetrahedral sites in a similar way as in Zr3NiOxDy. Both 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements of Fe-containing hydrides indicated weak hydrogen-induced magnetic ordering at low temperatures. The ordering temperatures of Zr3FeO0.2H6.52 and Zr3FeO0.6H6.25 are 105 and 140 K, respectively. [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]

• Ti x Zr 1−x La 0.03 Ni 1.2 Mn 0.7 V 0.12 Fe 0.12 (x = 0.12, 0.15, 0.18 and 0.22) alloys were studied as metal hydride battery anodes. • Annealed Zr/Ti-based AB 2 alloys crystallize with an FCC C15 Laves phase structure. • The maximum discharge capacity of the alloys as anode electrode of the MH battery reaches 466 mAh/g. • NPD shows that D atoms occupy the 96g sites only while V atoms occupy both 8 a and 16 d sites in AB 2 D 3.2 deuteride. • Cycling stability of the alloys show a clear dependence on their chemical composition. [Display omitted] The structural composition and electrochemical capacity of four AB 2 Laves-type intermetallic alloys with various Ti/Zr ratios (Ti x Zr 1−x La 0.03 Ni 1.2 Mn 0.7 V 0.12 Fe 0.12 , x = 0.12, 0.15, 0.18, and 0.22) were investigated in this study. The alloys were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. These data revealed the coexistence of the main phase of the C15-type FCC Laves-type AB 2 compounds with a secondary La–Ni intermetallic that was present in minor amounts. Increasing the Ti substitution for Zr caused the gradual shrinkage of the unit cells of the C15 phase. The neutron powder diffraction studies demonstrated that in the trihydride (Ti , Zr, V)(Ni, Mn, Fe, V) 2 D 3.2 , D atoms filled A 2 B 2 tetrahedra, whereas V atoms occupied not only conventional 16 d sites but also partially replaced Zr/Ti at 8 a sites. All studied alloys showed similar activation behaviors, wherein four cycles were required to realize the highest electrochemical capacity of the anodes. The Ti12/Zr88 alloy demonstrated excellent full discharge capacity that reached 466 mAh/g. The Ti22/Zr78 alloy electrode exhibited good cycling stability (retention rate of ~71%) after 500 cycles and a superior high-rate discharge capability (retention rate of ~71%) at a discharge current density of 400 mA/g. The cycling of the Ti22/Zr78 alloy electrode was studied by electrochemical impedance spectroscopy (EIS) to understand the reasons for the deterioration of cycling capacity, which was related with the pulverization of the alloys and increase in irreversible capacity. [ABSTRACT FROM AUTHOR]

The parent Hf(Zr) 4 Fe 2 O x compounds and their saturated deuterides have been synthesized. The crystal structures of Hf 2 FeD 4 , Hf 4 Fe 2 O 0.3 D 6.34 , Hf 4 Fe 2 O 0.6 D 3.5 , Zr 4 Fe 2 O 0.25 D 8.5 and Zr 4 Fe 2 O 0.5 D 7.5 using both X-ray and neutron powder diffraction have been determined. Experimental data together with the analysis of the crystal structure of the deuterides indicate that oxygen content influences substantially on H(D)-storage capacity. The interesting phenomenon of local disorder of the metal matrix for the majority of the studied deuterides, which appears at certain concentrations of oxygen and hydrogen, was discovered and analysed. This disorder was in a good agreement with the 57Fe hyperfine data observed at low temperatures for Zr 4 Fe 2 O 0.25 D 9.9. [Display omitted] • The crystal structure of Hf(Zr) 4 Fe 2 O x deuterides was studied. • H-induced local disorder of the metal matrix was observed. • "Split" model was used to refine the structures correctly. • The observed disorder was in a good agreement with the 57Fe hyperfine data. [ABSTRACT FROM AUTHOR]

In the present work we have studied the bonding mechanism and magnetism in a hexagonal λ 1 −MgCo 2 Laves phase intermetallic formed at r A / r B = 1.280. Ab initio theoretical calculations for MgCo 2 using the projector-augmented wave method implemented in the VASP code showed that Mg carries a formal charge +1.7 |e| while Co atoms are also positively charged with around +0.7 |e| being donated to establish the interatomic covalent Co-Co bonding in a three-dimensional network of Co tetrahedra. MgCo 2 is a metallic conductor with ferromagnetic properties and T C =303 K. Neutron Powder Diffraction study showed a collinear ordering of the Co moments, their alignment along the c -axis of the hexagonal unit cell with an average moment of 1.51(2) μ B /atom Co. Ab initio computational studies indicate that the Co moments reach the experimentally observed value approx.1.5 μ B when the unit cell volume exceeds 160 Å3 (average Co-Co distances 2.43 Å). [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: “Hybrid” hydrogen storage, where hydrogen is stored in both the solid material and as a high pressure gas in the void volume of the tank can improve overall system efficiency by up to 50% compared to either compressed hydrogen or solid materials alone. Thermodynamically, high equilibrium hydrogen pressures in metal–hydrogen systems correspond to low enthalpies of hydrogen absorption–desorption. This decreases the calorimetric effects of the hydride formation–decomposition processes which can assist in achieving high rates of heat exchange during hydrogen loading—removing the bottleneck in achieving low charging times and improving overall hydrogen storage efficiency of large hydrogen stores. Two systems with hydrogenation enthalpies close to −20kJ/mol H2 were studied to investigate the hydrogenation mechanism and kinetics: CeNi5–D2 and ZrFe2−x Al x (x =0.02; 0.04; 0.20)–D2. The structure of the intermetallics and their hydrides were studied by in situ neutron powder diffraction at pressures up to 1000bar and complementary X-ray diffraction. The deuteration of the hexagonal CeNi5 intermetallic resulted in CeNi5D6.3 with a volume expansion of 30.1%. Deuterium absorption filled three different types of interstices, Ce2Ni2 and Ni4 tetrahedra, and Ce2Ni3 half-octahedra and was accompanied by a valence change for Ce. Significant hysteresis was observed between deuterium absorption and desorption which profoundly decreased on a second absorption cycle. For the Al-modified Laves-type C15 ZrFe2−x Al x intermetallics, deuteration showed very fast kinetics of H/D exchange and resulted in a volume increase of the FCC unit cells of 23.5% for ZrFe1.98Al0.02D2.9(1). Deuterium content, hysteresis of H/D uptake and release, unit cell expansion and stability of the hydrides systematically change with the amount of Al content. In the deuteride D atoms exclusively occupy the Zr2(Fe,Al)2 tetrahedra. Observed interatomic distances are Zr–D=1.98–2.11; (Fe, Al)–D=1.70–1.75Å. Hydrogenation slightly increases the magnetic moment of the Fe atoms in ZrFe1.98Al0.02 and ZrFe1.96Al0.04 from 1.9μB at room temperature for the alloy to 2.2μB for its deuteride. [Copyright &y& Elsevier]

Abstract: The paper focuses on structural chemistry of novel intermetallic hydrides with unusual structural properties. In such “anisotropic” hydrides, a huge expansion proceeds in a sole crystallographic direction and leads to a dramatic differentiation of the properties of the hydrides along the direction of the expansion and normal to it. The behaviour of the “anisotropic” hydrides is dominated by the metal–hydrogen and hydrogen–hydrogen interactions in contrast to the “conventional” intermetallic hydrides where the metal–metal interactions are the most important ones. In sharp contrast to the known crystal structures of intermetallic hydrides, in “anisotropic” hydrides deuterium atoms do not fill initially existing interstices but, instead, attract rare earth atoms into their surrounding and form new D-occupied sites. This paper will summarise our recent research on the “anisotropic” hydrides with a particular focus on two groups of materials: (a) RENiIn-based deuterides (RE=rare earth metal) containing the shortest known separation of hydrogen atoms in the structures of metal hydrides and (b) RENi3–(CeNi3) and RE2Ni7–(La2Ni7)-based deuterides which develop unusually large (59–63%) expansion of the constituent RENi2 layers. [Copyright &y& Elsevier]

Two hydrogenated intermetallics with the highest Al/Zr ratio among the hydrogen-absorbing Zr–Al compounds, Zr4Al3 and Zr3Al2, have been studied by synchrotron X-ray, powder neutron diffraction and thermal desorption spectroscopy. Initial intermetallic compounds are quite different with respect to Al–Al interactions and contain plain Kagome Al nets (Zr4Al3) or Al–Al pairs (Zr3Al2). In hexagonal Zr4Al3D2.68 (space group (s.g.) P6322; a=11.0017(4); c=11.1694(5) A˚) a 2a×2a×2c superstructure is formed as a result of deuterium ordering in half of the available Zr4 tetrahedra. These tetrahedra share common corners and edges and form layers separated by 6363 Al-nets. In tetragonal Zr3Al2D2.26 (s.g. P42/mnm; a=7.5970(3); c=7.2613(3) A˚) in addition to the completely filled Zr4 tetrahedra hydrogen partially occupies Zr3 triangular sites. Thermal stability of the studied deuterides and Zr–D bonding characteristics can be related to the size of the occupied Zr4 tetrahedra. Higher thermal stability of Zr3Al2D2.26 agrees well with the existence of large Zr4 sites and contrasts to the behavior of Zr4Al3D2.68 containing ‘contracted’ Zr4 tetrahedra and having weaker Zr–D bonds. [Copyright &y& Elsevier]

In situ neutron diffraction was employed to investigate the structural evolution of the electrode materials in an ICR 10440 commercial cylindrical lithium-ion battery, which has a discharge capacity of 360 mAh and a nominal voltage of 3.7 V. A three-phase mixture of Li(Ni,Mn,Co)O 2 , LiCoO 2 and LiMn 2 O 4 was identified as the active material of the cathode, with graphite acting as the anode material. The study revealed that the graphite anode underwent structural changes to form a series of insertion-type lithiated derivatives, with up to 12.7% volume expansion for the Li-saturated compound LiC 6 . The charge-discharge behavior was more complex for the cathode. Here, the charge process was associated with partial lithium depletion from the initially Li-saturated compounds, leading to volume shrinkage for Li(Ni,Mn,Co)O 2 , in contrast to (Ni,Mn)-free LiCoO 2 . Electrochemical discharge experiments performed under a fast regime (2 C) at 5, 25 and 45 °C revealed that the discharge capacity followed the trend of an increased diffusion rate of Li + ions in the electrolyte and Li atoms in both electrodes, being highest for 45 °C. At the lowest tested temperature (5 °C), a rapid drop in the discharge capacity took place using the same kinetic regime. [ABSTRACT FROM AUTHOR]

Our earlier study Yartys et al. (2015) showed that at high hydrogen pressures, hexagonal MgNi 2 undergoes a hydrogen assisted phase transition into the orthorhombic MoSi 2 -type structure. Here we report on a combined high resolution synchrotron and neutron diffraction investigation of the crystal structure of MgNi 2 D 3 , and ab initio calculation of its electronic structure that revealed the nature of the metal–hydrogen bonding. The diffraction data (293 and 1.8 K) are well described with a Cmca unit cell with H atoms filling the deformed octahedra Mg 4 Ni 2 and the positions within the buckled nets –Ni–H–Ni–H– penetrating through the structure. DFT and phonon calculations showed that the Cmca structure of MgNi 2 D 3 is the most stable, both from the electronic structure and the lattice dynamical arguments. The Bader charge analysis indicates an electronic transfer from Mg (−1.59e − ) to Ni (+0.21e − ), H1 (+0.55e − ) and H2 (+0.31e − ). The phonon dispersion curves of MgNi 2 H 3 show positive frequencies, indicating that the structure is mechanically stable. The calculated gross heat of formation for the Cmca phase of MgNi 2 H 3 is −37.3 kJ/mol-H 2 , which makes it more stable by 3 kJ/mol-H 2 than the prototype structures tested in Yartys et al. (2015). The stability of the Cmca crystal structure of MgNi 2 H 3 is enhanced by the formation of the directional Ni–H covalent bonds supplemented by the electron transfer from Mg to both Ni and H. The heat capacity as a function of temperature is obtained by phonon calculation in the quasi-harmonic approximation. [ABSTRACT FROM AUTHOR]

MgNi 2 intermetallic was synthesized by powder metallurgy and crystallizes with a Laves-type C 36 structure (space group P 6 3 / mmc (No. 194); a = 4.826; c = 15.832 Å). At 300 °C during interaction with hydrogen (deuterium) gas compressed to 2.8–7.4 GPa, a trihydride MgNi 2 H(D) 3.2 was synthesized. The trihydride remained metastable at ambient conditions allowing its structure, stability and magnetic properties to be studied. The formation of MgNi 2 H 3.2 is associated with a complete rebuilding of the initial hexagonal structure into the orthorhombic distorted MoSi 2 -type sublattice (space group Fmmm (No. 69); a = 4.55; b = 4.69; c = 8.80 Å). Neutron diffraction of the MgNi 2 D 3.2 demonstrated that D atoms fill sites having octahedral Mg 4 Ni 2 (D1/4 b ) and planar Ni2 (D2/8 f ) coordination. Within the framework of the density functional theory, density of states (DOS) calculations showed the formation of a structure around −10 to −6 eV caused by the chemical bonds of hydrogen and its 1 s states mainly via interaction with the 3 d states of Ni. Analysis of the electronic structure revealed a charge transfer from Mg to Ni, and to the H atoms. The calculated enthalpy of formation of MgNi 2 H 3 is about −30 kJ/mol-H 2 , which is consistent with the stability of the hydride at normal conditions. The initial sample contained a small amount of a secondary MgNi 3 intermetallic, which has been formed during the equilibrium interaction of magnesium and nickel at 800 °C. Thus this compound should be included in the phase diagram of the Mg–Ni system. MgNi 3 decomposes under high-temperature/high-pressure hydrogenation conditions and forms nickel monohydride. [ABSTRACT FROM AUTHOR]

Abstract: The Zr9V4SH∼23 hydride was synthesized by saturation from gaseous hydrogen at room temperature and 0.12 MPa hydrogen pressure. The measured hydrogen absorption capacity of the -Zr9V4S was 1.77 H/M. The refinement of the hydride structure with the use of X-ray powder diffraction data confirmed the preserved symmetry of the metallic matrix (sp.gr. /mmc, , , , , ,  Å3). The analysis of interstices in this compound revealed that without positioning hydrogen atoms in triangular Zr3 interstices it is impossible to model the structure of k-hydride with the experimentally observed capacity. Neutron powder diffraction study of the Zr9V4SD∼23 deuteride (sp.gr. , ,  Å) revealed deuterium atoms filling two tetrahedral and three triangular interstices. A full occupancy of only one site (D4) was observed in our sample giving the refined deuterium content of 20.8(2) D/f.u. Filling of the D4 site causes a displacement of the sulphur atoms from the three-fold axis (splitting of 2c to 6h position). [Copyright &y& Elsevier]

This work focused on studies of the phase composition and crystal structure of LaxMm1−xNi4.7Sn0.3 (x=0, 0.5 and 1.0) alloys, where Mm denotes La-rich mischmetal produced by Norsk Hydro ASA. The alloys have been studied using conventional powder and synchrotron X-ray diffraction (XRD), powder neutron diffraction and scanning electron microscopy (SEM). After annealing at 950 °C the alloys were nearly single-phase materials with small precipitations of RENiSn equiatomic intermetallics formed at grain boundaries. Hydrogen absorption–desorption studies at 298, 323 and 348 K showed (a) a ‘flat’ structure of the pressure–composition isotherms; (b) a rather broad range of working H storage capacities; (c) an increase of the plateau pressures and decrease in both enthalpy and entropy changes following an increase of the Mm content in the alloy; and (d) fast formation–decomposition rate. Desorption isotherms were approximated by a recently developed model of phase equilibria in the metal–hydrogen systems. In situ powder neutron diffraction studies of the system MmNi4.7Sn0.3–D2 show that in the region of α-solid solution deuterium insertion leads to a gradual increase of the unit cell volume reaching 1.9%. In the hexagonal β-MmNi4.7Sn0.3 D4.51 deuteride D atoms occupy two of four available types of tetrahedral interstices including 6m RE2(Ni,Sn)2 and 12n RE(Ni,Sn)3. [Copyright &y& Elsevier]