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- Moser, D, et al.
(författare)
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Structure and stability of high pressure synthesized Mg-TM hydrides (TM = Ti, Zr, Hf, V, Nb and Ta) as possible new hydrogen rich hydrides for hydrogen storage.
- 2009
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Ingår i: Journal of Materials Chemistry. ; 19:43, s. 8150-
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Tidskriftsartikel (refereegranskat)abstract
- A series of hydrogen rich Mg6–7TMH14–16 (TM = Ti, Zr, Hf, V, Nb and Ta) hydrides have been synthesized at 600 °C in a high pressure anvil cell above 4 GPa. All have structures based on a fluorite type metal atom subcell lattice with a ≈ 4.8 Å. The TM atom arrangements are, however, more ordered and can best be described by a superstructure where the 4.8 Å FCC unit cell axis is doubled. The full metal atom structure corresponds to the Ca7Ge type structure. This superstructure was also observed from electron diffraction patterns. The hydrogen atoms were found from powder X-ray diffraction using synchrotron radiation to be located in the two possible tetrahedral sites. One coordinates three Mg atoms and one TM atom and another coordinates four Mg atoms. These types of new hydrogen rich hydrides based on immiscible metals were initially considered as metastable but have been observed to be reversible if not fully dehydrogenated. In this work, DFT calculations suggest a mechanism whereby this can be explained: with H more strongly bonded to the TM, it is in principle possible to stepwise dehydrogenate the hydride. The remaining hydrogen in the tetrahedral site coordinating the TM would then act to prevent the metals from separating, thus making the system partially reversible
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| 5. |
- Sato, Toyoto, et al.
(författare)
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Structural investigations of two new ternary magnesium–niobium hydrides, Mg6.5NbH~14 and MgNb2H~4
- 2006
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 417:1-2, s. 230-234
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Tidskriftsartikel (refereegranskat)abstract
- Two new magnesium–niobium hydrides, Mg6.5NbH14 with a face centred cubic unit cell a = 9.548(1) Å (space group (No. 225), Z = 4, V = 870.49 Å3) and MgNb2H4 with a C-centred monoclinic unit cell a = 5.685 (4) Å, b = 3.2914(6) Å, c = 7.924(2) Å and β = 103.82(3)° (space group C2/m (No. 12), Z = 2, V = 143.98 Å3), were synthesized by reacting MgH2 and Nb in a high-pressure anvil cell at 8 GPa and 600 °C. The structures of the new hydrides were refined from synchrotron radiation data. Mg6.5NbH14 has a structure related to Mg7TiH16 (a = 9.532(2) Å space group (No. 225)) (D. Kyoi, T. Sato, E. Rönnebro, N. Kitamura, A. Ueda, M. Ito, S. Katsuyama, S. Hara, D. Noréus, T. Sakai, J. Alloys Compd. 372 (2004) 213). Where the metal atom structure is of the Ca7Ge type. Mg6.5NbH14, however, has some vacancies on one of the magnesium sites similar to the recently discovered Mg6VH14 (D. Kyoi, T. Sato, E. Rönnebro, Y. Tsuji, N. Kitamura, A. Ueda, M. Ito, S. Katsuyama, S. Hara, D. Noréus, T. Sakai, J. Alloys Compd. 375 (2004) 253). The metal atoms in MgNb2H4 have the AuTe2 type structure.
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