Novel phases RE 11Co4In9 (RE = Pr, Nd, Sm, Tm, Lu) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T = 870 K for 1,500 h in evacuated and sealed silica ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The structure of the Pr11Co4In9 compound was refined from powder X-ray diffraction patterns using the FullProf program package. The compound crystallizes in Nd11Pd4In9 type structure (orthorhombic space group Cmmm, Z = 2; a = 14.801(10); b = 22.119(14); c = 3.746(2) & Aring;) and belongs to a large family of two-layer structures (with layers perpendicular to the short unit cell axis) based on the intergrowth of AlB2- and CsCl-type related slabs. Pr11Co4In9 - together with the Mo2FeB2, Mn2AlB2, o-La2Ni2In, Lu5Ni2In4 types structure, in which the ternary indides crystallize - forms a homologous series RE m+n T 2n X m, where m is the number of REX (CsCl type) slabs and n the number of RET 2 (AlB2 type) slabs (T = Co, X = In). For Pr11Co4In9 the values are m = 18, n = 4. The isostructural compounds were obtained with Nd, Sm, Tm, Lu and complete the series of RE 11Co4In9 (RE = Sc, Y, Gd, Tb, Dy, Ho, Er) compounds. The electronic structure calculations were performed by means of the TB-LMTO-ASA program indicating a covalent interaction between In1-In1 atoms and metallic bonding between other In, Pr and Co atoms.

Mg17Al12 is a binary magnesium-based intermetallic compound that demonstrates favourable hydrogenation behaviour with a potential for practical hydrogen-storage applications. Although the hydrogenation properties of Mg17Al12 have been extensively studied, the enhancement of these properties through other metals as additives remains relatively underexplored. We present structural and hydrogenation investigations of the composite materials based on the binary Mg17Al12 alloy and the yttrium substituted ternary Mg17Al12-Y composition, using gas phase hydrogenation methods, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray powder diffraction (XRPD). The Mg17Al12 alloy absorbs more than 1.8 and 3.4 wt% H2 at 350 degrees C during 15 and 65 h, respectively. Under the same conditions, the yttrium-substituted (0.7 wt%) Mg17Al12-Y absorbs 2.5 and 4.4 wt% H2.

The intermetallic phases RE3Co9In2 (RE = Pr, Nd, Sm) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T = 600 degrees C for 1,500 h in evacuated and sealed quartz ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The crystal structure of Pr3Co9In2 was refined from powder X-ray diffraction data using the Fullprof program package. The compound crystallizes in a Sm2Co9In3-related structure type (orthorhombic space group Cmmm, Z = 2; a = 23.123(4); b = 5.1003(7); c = 4.0423(5) & Aring;) and is a two-layer structure with layers perpendicular to the z direction. The crystal structure of Pr3Co9In2 is based on the intergrowth of CaCu5- and CsCl-type related slabs and is a member of the homologous series RE2m+2n+2pT2m+2nX2n+2p, where m and n are the numbers of RET5 and RET4X (CaCu5 type) slabs and p is the number of REX (CsCl type) slabs (T = Co, X = In), respectively. For Pr3Co9In2 the values are m = n = p = 2. Isostructural compounds were obtained with Nd and Sm.

Abstract Novel phases RE 11 Co 4 In 9 ( RE = Pr, Nd, Sm, Tm, Lu) were obtained by arc-melting of the elements in an argon atmosphere followed by annealing at T = 870 K for 1,500 h in evacuated and sealed silica ampoules. All samples were characterized through their powder X-ray diffraction patterns and metallographic and quantitative phase analyses. The structure of the Pr 11 Co 4 In 9 compound was refined from powder X-ray diffraction patterns using the FullProf program package. The compound crystallizes in Nd 11 Pd 4 In 9 type structure (orthorhombic space group Cmmm , Z = 2; a = 14.801(10); b = 22.119(14); c = 3.746(2) Å) and belongs to a large family of two-layer structures (with layers perpendicular to the short unit cell axis) based on the intergrowth of AlB 2 - and CsCl-type related slabs. Pr 11 Co 4 In 9 - together with the Mo 2 FeB 2 , Mn 2 AlB 2 , o-La 2 Ni 2 In, Lu 5 Ni 2 In 4 types structure, in which the ternary indides crystallize – forms a homologous series RE m+n T 2n X m , where m is the number of REX (CsCl type) slabs and n the number of RET 2 (AlB 2 type) slabs ( T = Co, X = In). For Pr 11 Co 4 In 9 the values are m = 18, n = 4. The isostructural compounds were obtained with Nd, Sm, Tm, Lu and complete the series of RE 11 Co 4 In 9 ( RE = Sc, Y, Gd, Tb, Dy, Ho, Er) compounds. The electronic structure calculations were performed by means of the TB-LMTO-ASA program indicating a covalent interaction between In1–In1 atoms and metallic bonding between other In, Pr and Co atoms.

The ternary boride MgNi 2 B 6 (magnesium dinickel hexaboride) crystallizes as a new representative of the CeCr 2 B 6 structure type. The Mg and Ni atoms occupy sites with mmm and mm 2 symmetry, respectively. The B atoms occupy two sites with m .. and m 2 m symmetry. The 14-membered polyhedron around the Mg atom is a hexagonal prism, with two adjacent lateral faces centred by Mg atoms. The Ni atoms are encapsulated in 10-vertex polyhedra. The trigonal prismatic coordination is typical for both B atoms. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation (TB–LMTO–ASA) method. The electron concentration is higher around the B atoms, which form eight-membered channels along b , which are filled with Mg and Ni atoms. The maximum hydrogen absorption is up to 2.38 wt% H 2 .

This work is devoted to a complete structural study of the single crystal of the known ternary compound Nd2LiGe6, belonging to the structural type Pr2LiGe6, the Pearson symbol oS18, the spatial group Cmmm and for it the periods of the elementary cell are established (a = 0,41674(1), b = 2,11087(7), c = 0,43713(1) nm). The experiment was conducted on the Xcalibur diffractometer from Oxford Diffraction, equipped with a CCD detector Sapphire2 and Mo Кα-radiation source ENHANCE. The structure of the compound was solved by a direct method. The program was SHELX-97 used to clarify the coordinates of atoms and their thermal parameters. The mixture of crushed components, which was weighed to an accuracy of 0.001 g and a total weight of 1,000 g, was thoroughly mixed and pressed into granules. The samples were placed in a tantalum crucible, heated in an induction furnace to 400 ºС at a rate of 5 ºС per minute and held for 48 hours. The next stage of the experiment was to heat the samples to 800 °C, anneal them for 6 hours, followed by slow cooling to room temperature. The homogenizing annealing procedure for all 12 alloys was performed at 400 °C for three weeks. Analysis of single crystal data showed that the Nd2LiGe6 phase crystallizes in orthorhombic syngony, the spatial group Cmmm, with 18 atoms in the unit cell. In the crystal structure, neodymium atoms occupy position 4i, while lithium atoms are localized in position 2a, Ge1 and Ge2 atoms occupy position 4j, while Ge3 atoms are located in position 4i. The results of the calculation of electron structures show that Nd and Li atoms are electron donors for Ge atoms. As a result, around neodymium and lithium there is a positive charge, and around Germanium atoms in the studied triple phase – negative. There is a slightly higher filling of electronic states at the Fermi level for Nd2LiGe6 compared to related tetrar phases. It was found that in the synthesized intermetallic compound, in addition to the main metal bond, there are also covalent bonds.

The ternary boride MgNi2B6 (magnesium dinickel hexaboride) crystallizes as a new representative of the CeCr2B6 structure type. The Mg and Ni atoms occupy sites with mmm and mm2 symmetry, respectively. The B atoms occupy two sites with m.. and m2m symmetry. The 14-membered polyhedron around the Mg atom is a hexagonal prism, with two adjacent lateral faces centred by Mg atoms. The Ni atoms are encapsulated in 10-vertex polyhedra. The trigonal prismatic coordination is typical for both B atoms. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation (TB-LMTO-ASA) method. The electron concentration is higher around the B atoms, which form eight-membered channels along b, which are filled with Mg and Ni atoms. The maximum hydrogen absorption is up to 2.38 wt% H2.

The crystal structure of magnesium nickel tetraboride, MgNiB4, was solved and refined based on single-crystal X-ray diffraction data. MgNiB4 crystallizes in the Pbam space group [a = 5.8791 (2), b = 11.2982 (5) and c = 3.2771 (1) Å] and is isostructural with the YCrB4 type. The MgNiB4 and YCrB4 structures both belong to the AlB2-type structural family, for which the formation of 63-nets by B atoms is typical. In MgNiB4, B atoms form five- and seven-membered ring nets, which result from a rearrangement of the 63-nets. Strong covalent B-B interactions are established according to electronic structure calculations using the tight-binding linear muffin-tin orbital atomic spheres approximation (TB-LMTO-ASA) method. The maximum hydrogen absorption by the MgNiB4 alloy reached 3.75 wt% H2.

Tb0.82Sm0.18Ni0.83Co0.17Mg, orthorhombic, Cmcm (no. 63), a = 3.6707(4) & Aring;, b = 17.723(1) & Aring;, c = 3.9863(4) & Aring;, V = 259.33 (4) & Aring;3, Z = 4, R gt (F) = 0.0334, wR ref (F2) = 0.0861, T = 293 (2) K.

An isothermal cross-section of the Zr-Cu-Bi phase diagram at 400 degrees C was constructed by phase identification and analysis of 43 annealed ternary alloys. Scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) studies were performed. Based on the above-mentioned studies, the area of existence of six phases was established: t1 - Zr5CuBi3, t2 - Zr5CuBi2, t3 - ZrCuBi, t4 - Zr2CuBi, t5 - Zr2Cu3Bi, t6 - ZrCu2Bi, and the phase equilibria between them were determined. The extent of solid solutions based on binary compounds was determined. The electronic structures of the compounds were calculated using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method using experimental crystallographic data reported here.

The ternary magnesium/lithium boride, MgxLi3 − xB48 − y (x = 1.11, y = 0.40, idealized formula MgLi2B48), crystallizes as its own structure type in P43212, which is closely related to the structural family comprising α-AlB12, Be0.7Al1.1B22 and tetragonal β-boron. The asymmetric unit of title structure contains two statistical mixtures Mg/Li in Wyckoff sites 8b with relative occupancies Mg:Li = 0.495 (9):0.505 (9) and 4a with Mg:Li = 0.097 (8):0.903 (8). The boron atoms occupy 23 8b sites and two 4a sites. One of the latter sites has a partial occupancy factor of 0.61 (2). Both unique Mg/Li atoms adopt a twelvefold coordination environment in the form of truncated tetrahedra (Laves polyhedra). These polyhedra are connected by triangular faces to four [B12] icosahedra. The boron atoms exhibit four kinds of polyhedra, namely pentagonal pyramid (coordination number CN = 6), distorted tetragonal pyramid (CN = 5), bicapped hexagon (CN = 8) and gyrobifastigium (CN = 8). At the gas hydrogenation of MgLi2B48 alloy, formation of the eutectic composite hydride LiBH4+Mg(BH4)2 and amorphous boron is observed. In the temperature range 543–623 K, the hydride eutectics decompose, forming MgH2, LiH, MgB4, B and H2.

Alloys from the regions of existence of the solid solutions RxTb2-xNi17 and Tb2Ni17-yMy were synthesized by arc-melting with further annealing at 400 ºС. Quantitative and qualitative composition of alloys and powders of electrode materials was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Tb/R/Ni and Tb/Ni/Mg ratio in the samples was confirmed also by X-ray fluorescence spectroscopy. The cell parameters of RxTb2-xNi17 (x = 0.5) ternary phases are: a = 8.2987(9) Å, c = 8.0206(8) Å, V = 478.37(9) Å3 for R = Zr, a = 8.3161(6) Å, c = 8.0482(8) Å, V = 482.03(6) Å3 for R = Y and a = 8.3690(6) Å, c = 8.0560(7) Å, V = 488.66(6) Å3 for R = La. Tb atoms were partially substituted by Y, Zr and La atoms because of closeness of atomic radii size. Under experimental condition capacity parameters were 1.81 H/f.u. for the Zr-containing electrode, 2.29 H/f.u. for the Y-containing electrode and 2.31 H/f.u. for the La-containing electrode. In the case of Li,Mg co-doped electrodes we observed more than 2.5 H/f.u. Cell parameters of the Zr- and La-containing phases after hydrogenation increased isotropically. Synthesized hydrides can be interpreted as superstructures with the Tb2Mn17C2.5-type (filled-up of Th2Ni17). The Y0.5Tb1.5Ni17-based electrode demonstrates the potential corrosion at -0.540 V, electrodes with the compositions Zr0.5Tb1.5Ni17 and La0.5Tb1.5Ni17 show -0.413 V and -0.405 V, respectively. Li and Mg-codoped electrodes shoved the corrosion potential -0.410 V (Tb2Ni16.4Li0.2Mg0.4) and -0.550 V for Tb2Ni15.6Li0.6Mg0.8, respectively.

The structural and hydrogenation properties of Mg2Sn0.6Ni0.4 and Mg2Sn0.6Sb0.4 intermetallics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), gas and electrochemical hydrogenation techniques. The synthesized alloys are from the homogeneity ranges of solid solutions based on Mg2Sn binary compound with cubic anti-fluorite Na2O-type structure. The structural studies by powder diffraction method revealed that Ni and Sb atoms replace the Sn atoms in 4a site. Both ternary phases effectively passivate in 6 M KOH over a wide potential range. The presence of Ni or Sb in the solid solutions improves the corrosion resistance of Mg2Sn0.6Ni0.4 and Mg2Sn0.6Sb0.4 compared to the binary compound Mg2Sn. Two sloping plateaus are observed on the p-c-T diagrams of both samples indicating that the hydride formation is realized in a two-stage process. The first stage corresponds to the insertion of hydrogen in structural voids of the intermetallic matrix with the formation of Mg2Sn0.6Ni0.4H3.6 or Mg2Sn0.6Sb0.4H3.4 hydrides. The second stage is the subsequent hydrogenation of the formed hydrides with the following decomposition to simpler hydrides MgH2 and Mg2NiH4 and small amounts of elemental tin or Sn0.6Sb0.4 phase.

The gas-phase and electrochemical hydrogenation properties of Nd0.5Y0.5MgNi4-xCox (where x varies from 0 to 3) were studied. Samples were prepared using sintering and annealing procedures. X-ray diffraction analysis indicated that all the alloys were single-phase. The alloys readily absorbed hydrogen, and the crystal structures of the resulting saturated hydrides were refined. Nd0.5Y0.5MgNi4H4.2 and Nd0.5Y0.5MgNi3CoH4.4 belong to the NdMgNi4H3.6 structural type, while Nd0.5Y0.5MgNi2Co2H5.5 and Nd0.5Y0.5MgNiCo3H6.0 belong to the LaMgNi4H4.85 structural type. Electrochemical studies revealed that the maximum discharge capacity of Nd0.5Y0.5MgNi4-xCox electrodes increased from 236 mAh/g to 328 mAh/g as the cobalt content increased. The high-rate dischargeability (HRD1000) initially decreased from 48 % to 7 % with increasing cobalt content, but then increased to 32 % at the highest cobalt concentration. Additionally, the electrochemical kinetic properties were determined and compared for these electrodes, including the charge-transfer resistance (R-ct), polarization resistance (R-p), exchange current density (I-0), limiting current density (I-L), and hydrogen diffusion coefficient (D-H).

In this article, we provide an overview of hydrogen storage materials, taking our previous results as examples. Towards the end of the paper, we present a case study in order to highlight the effects of substitutional alloying, compositional additives, and nanostructuring on the hydrogen sorption properties of magnesium-based intermetallics. Specifically, partial substitution of Mg by Li and d-elements by p-elements leads to structural changes, inducing disorder and the formation of high-entropy alloys. Our approach showcases the methodology to enhance the H2-capacity and to provide a positive boost to the H2-storage performance, including lower temperatures of H2 desorption, better thermodynamics and kinetics, lower temperatures of hydrogen uptake/ release for Metal-Hydride Hydrogen Storage (MHHS) systems and higher capacity of anodes for Metal-Hydride batteries (MHB) together with lower prices of raw materials.

The ternary germanide Mg5.57Ni16Ge7.43 (cubic, space group Fm\overline{3}m, cF116) belongs to the structural family based on the Th6Mn23-type. The Ge1 and Ge2 atoms fully occupy the 4a (m\overline{3}m symmetry) and 24d (m.mm) sites, respectively. The Ni1 and Ni2 atoms both fully occupy two 32f sites (.3m symmetry). The Mg/Ge statistical mixture occupies the 24e site with 4m.m symmetry. The structure of the title compound contains a three-core-shell cluster. At (0,0,0), there is a Ge1 atom which is surrounded by eight Ni atoms at the vertices of a cube and consequently six Mg atoms at the vertices of an octahedron. These surrounded eight Ni and six Mg atoms form a [Ge1Ni8(Mg/Ge)6] rhombic dodecahedron with a coordination number of 14. The [GeNi8(Mg/Ge)6] rhombic dodecahedron is encapsulated within the [Ni24] rhombicuboctahedron, which is again encapsulated within an [Ni32(Mg/Ge)24] pentacontatetrahedron; thus, the three-core-shell cluster [GeNi8(Mg/Ge)6@Ni24@Ni32(Mg/Ge)24] results. The pentacontatetrahedron is a new representative of Pavlyuk's polyhedra group based on pentagonal, tetragonal and trigonal faces. The dominance of the metallic type of bonding between atoms in the Mg5.57Ni16Ge7.43 structure is confirmed by the results of the electronic structure calculations. The hydrogen sorption capacity of this intermetallic at 570 K reaches 0.70 wt% H2.

La12Mg46LiMn, cubic, Fm3‾m $Fm\overline{3}m$ (no 225), a = 14.7119(3) Å, V = 3184.24(19) Å3, Z = 2, R gt(F) = 0.0330, wR ref(F 2) = 0.0601, T = 293(2) K.

The ternary Tb2-xNdxZn17-yNiy (x = 0.5, y = 4.83) disordered phase belongs to the structural family based on the rhombohedral Th2Zn17 structure type. The structure is maximally disordered since all the sites are occupied by statistical mixtures of atoms. The Tb/Nd mixture of atoms occupies the 6c site (site symmetry 3m). The statistical mixtures Ni/Zn consisting of more Ni atoms are located in the 6c and 9d (symmetry .2/m) sites. In the following 18f (site symmetry .2) and 18h (site symmetry .m) sites are located Zn/Ni statistical mixtures which consist of more Zn atoms. Zn/Ni atoms form three-dimensional networks with hexagonal channels that fill statistical mixtures of Tb/Nd and Ni/Zn. The Tb2-xNdxZn17-yNiy compound belongs to the family of intermetallic phases capable of absorbing hydrogen. In the structure, there are three types of voids, namely, 9e (site symmetry .2/m), 3b (site symmetry -3m) and 36i (site symmetry 1), in which hydrogen can be inserted, and the maximum total absorption capacity can reach 1.21 wt% H2. Electrochemical hydrogenation shows that the phase absorbs 1.03% of H2, which indicates partial filling of the voids with H atoms.