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Abstract : A study of hydrided tantalum metal is reported, using the high-resolution 6.2-keV resonance of 181Ta 1. With a single-line source of 181WMATH the isomer shift S was measured as a function of the hydrogen concentration c of a tantalum metal absorber c is defined as the H-Ta atom ratio. The tantalum metal foils were hydrided electrolytically ; c was derived from the relative change of the lattice constant, Ɗa-a, as obtained by X-ray diffraction. Within the studied concentration range from c = 0 to c = 0.147 S increases by 10 mm-s, which corresponds to about 80 experimental linewidths. The change in S can be approximated by a straight line with a slope of dS-dc = + 62 mm-s indicating a decrease of ρ0 with increasing c. The observed value of dS-dc arises from two contributions : 1 the volume change and 2 the explicit change in the electronic structure at the tantalum. The first is to be estimated from hydrostatic pressure experiments with Ta-metal 1 ; it can account for about one third of dS-dc. An explicit decrease of ρ0 with increasing hydrogen concentration is thus present. Using electron densities from Dirac-Fock calculations for free-ion configurations of Ta J. B. Mann, Los Alamos, private communication 1972, we conclude that between 50 % and 100 % of the hydrogen electrons must be filling up empty 5d-conduction-electron states of Ta.





Autor: A. Heidemann G. Kaindl D. Salomon G. Wortmann

Fuente: https://hal.archives-ouvertes.fr/



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