Zusammenfassung
A novel gas pressure cell for in situ neutron powder diffraction has been developed. It is based oil a single crystal sapphire tube as a sample holder, allows a 360 degrees unobstructed access by the neutron beam and has little background contribution. This device was used to study the hydrogenation of alpha-MgPd3, Which undergoes a hydrogen driven rearrangement from a ZrAl3 to a AuCu3 type ...
Zusammenfassung
A novel gas pressure cell for in situ neutron powder diffraction has been developed. It is based oil a single crystal sapphire tube as a sample holder, allows a 360 degrees unobstructed access by the neutron beam and has little background contribution. This device was used to study the hydrogenation of alpha-MgPd3, Which undergoes a hydrogen driven rearrangement from a ZrAl3 to a AuCu3 type structure. Deuterium could be located and a strong preference of [Pd-6] voids was found in alpha-MgPd3D0.79 under 5 bar and in alpha-MgPd3D0.94 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 alpha-MgPd3, Which is complete at temperatures below 450 K, and the transformation to the hydride of cubic beta-MgPd3, starting around 550 K, are exothermic. This completion of the hydrogenation-dehydrogenation series of MgPd3 suggests, that the rearrangement of the metal structure proceeds by a hydrogen assisted gliding mechanism with a shift vector of 1/2[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.
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