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In situ Neutron Powder Diffraction on Intermediate Hydrides of MgPd 3 in a Novel Sapphire Gas Pressure Cell
Author(s) -
Kohlmann Holger,
Kurtzemann Nadine,
Weihrich Richard,
Hansen Thomas
Publication year - 2009
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200900336
Subject(s) - neutron diffraction , hydrogen , materials science , superstructure , crystallography , bar (unit) , deuterium , hydride , dehydrogenation , sapphire , crystal structure , chemistry , metal , atomic physics , metallurgy , thermodynamics , geology , optics , physics , laser , catalysis , organic chemistry , biochemistry , oceanography
A novel gas pressure cell for in situ neutron powder diffraction has been developed. It is based on a single crystal sapphire tube as a sample holder, allows a 360° unobstructed access by the neutron beam and has little background contribution. This device was used to study the hydrogenation of α‐MgPd 3 , which undergoes a hydrogen driven rearrangement from a ZrAl 3 to a AuCu 3 type structure. Deuterium could be located and a strong preference of [Pd 6 ] voids was found in α‐MgPd 3 D 0.79 under 5 bar and in α‐MgPd 3 D 0.94 under 20 bar deuterium pressure. The crystal structure may be described as a new defect superstructure variant of the NaCl type. In situ thermal analysis under 5 bar hydrogen pressure showed that both the hydrogen uptake of α‐MgPd 3 , which is complete at temperatures below 450 K, and the transformation to the hydride of cubic β‐MgPd 3 , starting around 550 K, are exothermic. This completion of the hydrogenation‐dehydrogenation series of MgPd 3 suggests, that the rearrangement of the metal structure proceeds by a hydrogen assisted gliding mechanism with a shift vector of ${1 \over 2}$ [110]. This is also supported by quantum chemical calculations, which show a decohesion of the intermetallic structure upon hydrogenation accompanied by the appearance of Pd–H bonding interactions.