ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The phase diagrams and crystal structures of V, Nb, Ta (= M) hydrides and deuterides show a close relationship, with some substantial differences at lower temperatures. At high temperatures ( ̃500 K) H atoms form a disordered solid solution at tetrahedral interstices of a b.c.c. metal lattice in the composition range MHx with 0 〈 x ∼ 1 (α-MH). At lower temperatures (3̃00 K) the composition is limited to a non-stoichiometric solid solution MH0.5-MH. The H ordering in ζ-NbH (β-TaH structure, composition MH0.5, space group C222) and γ-NbH (MH, I{\bar 4}m2) is closely related to β-NbH (MH,Cccm). The symmetry is lowered to B2/m (β-VH structure, MH0.5) for a similar distribution of H at octahedral interstices. The crystal structures can be characterized by the translation vectors T1 (½ ½ ½) and T2 (0 ½ ½) between nearest H atoms, α-MH exhibits a short-range order with a preference of T1 and T2 between neighbouring H atoms. In MH0.5-MHss the percentage [T] of T1 and T2 translations changes with composition and temperature. The different low- temperature phases and the order-disorder transitions can be characterized by the ratio [T1]/([T1] + [T2 ]).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739478000790
Permalink
