SUBSTITUTION EFFECTS ON MIXED-VALENCE IN TERNARY INTERMETALLICS

We report here the changes in the europium valence in Eu1-xLnxPd2Si2 (Ln = La, Y, Yb; 0 less-than-or-equal-to x less-than-or-equal-to 0.95) as studied by L(III) absorption edge spectroscopy. On the basis of the simple unit-cell volume considerations and from the fact that the unit-cell volume of EuPd2Si2 is intermediate between that of LaPd2Si2 and Y(Yb)Pd2Si2, one expects the europium valence to vary in both cases as a function of x, with the variation taking place in the opposite directions in the two pseudoternaries Eu1-xLaxPd2Si2 and Eu1-2xY(Yb)xPd2Si2. However, we find that the valence does not change as a consequence of lanthanum substitution and increases with the addition of yttrium (ytterbium). These results are discussed in terms of the local environment of europium atoms in these systems.