Etude De l'Ytterbium Et Des Alliages Ytterbium-Baryum Sous Haute Pression A Basse Temperature

Abstract

Resistivity measurements have been performed under pressure in 99,95% pure Yb and Yb alloys with Ba concentration ranging from 1 to 14.5 at%. It has been found that the f.c.c. phase is stable in the solid solution up to ∼ 20 at%. From resistivity measurements we have found that alloying with Ba increases the metallic character of Yb. The strong quadratic temperature dependence of the resistivity in pure Yb from 4.2 to 35°K increases with pressure as long as Yb remains a semi-metal (0–11 kbar). The negative temperature coefficient observed in the alloys is attributed to a temperature independent mobility governed by the scattering against divalent Ba atoms and to the excitation of the carriers in the small overlap semi-metal. The density vs. pressure for the residual free carriers is obtained from Matthiessen's rule and is in agreement with direct estimation given by the transport properties measurements under pressure. The density of carriers for the alloys has been deduced from Nordheim's rule and allows us to give predictions about the hypothetical f.c.c. phase of Ba. We suggest that the metallic character of Yb is connected with the strong hybridization between the s-p and d bands near the Fermi level. This fact is in good qualitative agreement with the R.A.P.W. band calculation of Johansen and Mackintosh.