Fermi energy effects on absorption of hydrogen in LaNi5 and LaCo5 alloys

The electronic state of hydrogen in LaNi5 and LaCo5 is different from that in Pd in that lower H states are entered by electrons from the Fermi level of the alloy, emptying rather than filling the conduction band. However, the successive lowering of the Fermi level occurring here will contribute to...

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Bibliographic Details
Published in:Journal of alloys and compounds 1995-12, Vol.231 (1-2), p.454-459
Main Authors: Yasuda, K., Brodowsky, H.
Format: Article
Language:English
Subjects:
AB5-type alloy
Band structure
Fermi energy
Fundamentals
Theory
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Summary:The electronic state of hydrogen in LaNi5 and LaCo5 is different from that in Pd in that lower H states are entered by electrons from the Fermi level of the alloy, emptying rather than filling the conduction band. However, the successive lowering of the Fermi level occurring here will contribute to a rise of the chemical potential of the dissolved hydrogen in much the same way as in palladium. In the case of LaNi5, this Fermi energy contribution cannot be separated from the elastic interaction, which predominates in the whole concentration range and leads to the formation of several two-phase regions. Besides the elastic interaction (and the electronic contribution hidden beneath it), the availability of multiple interstitial sites and the blocking effect between some densely packed sites contribute to the thermodynamics of the system. In the case of LaCo5, an abrupt rise of the chemical potential of 6.3 kJ molH−1 is observed at the composition of LaCo5H3, well within the range of occupation of 4e sites. It is suggested that the rise at this perfectly stoichiometric composition is related to the band structure of the alloy.
ISSN:0925-8388
1873-4669
DOI:10.1016/0925-8388(96)80005-3