The electronic structure of Sm and Gd in Sm 1-xGd xS has been experimentally studied. Besides the well known strong increase of Sm valence at x » 0.15 (associated with the electronic transition to the mixed valence state), a decrease of Sm valence for x>0.9 has been observed for the first time (Fig.11). This phenomenon is explained as the 4f-5d hybridization on neighboring Sm atoms involved in the onset of the mixed valence state, and is interpreted as a manifestation of parity non-violation.
Fig. 11. Dependence of the samarium valency on the composition (x) in Sm1-xGd xS: b is the curve, fitting the experimental points, c is the calculated one
The electronic structure of U and Ge in the solid solutions U(Al1-xGex)3 is investigated. It is shown that uranium has the mixed valence U3+[Rn](5f3) - U4+ [Rn](5f2) over the composition range (0£ x £1) (here [Rn] indicates the closed shell of the radon atom) and the population of the uranium 5f shell increases by » 0.28 5f-electrons/U atom from UAl3 (x = 0) to UGe3 (x = 1) (see Fig. 12). The electronic structure of Ge is close to the electronic structure of Ge metal in the whole composition range (0£ x £ 1). No variation of the population of the Ge 4p-shell is detected to within the experimental error (» 0.1 4p-electrons/Ge atom) for x from 0.2 to 1. It is established that the delocalization of a U 5f- electron occurs as a result of its transition to the s or d band of the same uranium atom.
Fig. 12. Dependence of the uranium 5f-shell population (n5f) on the composition (x) in U(Al1-xGex)3 according to shifts of the U La1 lines
The population of the 4f, 5d, and 6s shells of rare-earth atoms in RHx hydrides (R = Ce, Sm, Yb; x » 2¸3) has been studied. The population of the 5d and 6s shells of Ce and Sm atoms, and the charge on them in metals and hydrides, were determined from experiment and calculated within the Hartree-Fock-Dirac (Koopmans) model. The decrease of the charge on Ce and Sm revealed upon transition from the metal to the hydride argues unambiguously for the anionic (hydride) model. In YbHx with x >2, the structural transition (Fig. 13) is accompanied by a strongly pronounced electronic transition from divalent to a noninteger-valence state.
Fig. 13. Dependence of the valency of ytterbium on the composition (x) in YbHx.
The X-ray line shift method has been used to study the electronic state of Ce (the 4f population) and of its 3d, 4d and 5d partners in the CeM2 Laves phases (M = Fe, Co, Ni, Ru, Rh, Os, Pt, Mg, Al). It is shown that the valence of Ce in CeM2 decreases monotonically from the limiting value m » 3.35 to m » 3 with decreasing intracrystalline compression of Ce atoms (Fig. 14). The population of the outer 4d and 5d orbitals of Ru, Rh, and Os in the Laves phases has been found to be larger than that in metals.
Fig. 14. Dependence of the cerium valence on the effective metallic radius of the Ce in the compound
The shifts of the Ka1 and Kb1 lines of all rare-earth (RE) metals (from La to Lu) have been measured experimentally by the X-ray shift method. The population of the RE-metal 6s and 5d shells has been deter-mined by comparing the experimental and theoretical shifts obtained within the Dirac-Fock (Koopmans) model. Trivalent metals exhibit a monotonic crossover from the 6s»2 5d»1 to 6s»15d»2 configuration with increasing atomic number (see Fig. 15).
Fig 15. Dependence of the population of the RE-metal 6s (ns) and 5d (nd) shells on the atomic number (Z)