The distribution on the doped holes in La 2-xSrxCu1-yRuyO4'

We present a systematic study of the perovskite-related system La2-xSrxCu1-yRuyO4-delta using Cu L-2,L-3, Ru L-2,L-3, and O K X-ray absorption spectroscopy (XAS), magnetic and electrical measurements. This system can be regarded as hole-doped via substitution of La by Sr and to be electron-doped via substitution of Ru by Cu, and thus the question as to the distribution of the charge carriers and the interaction between Cu and Ru ions are central to our understanding of these novel systems. The comparison of the experimental data with the crystal-field-multiplet calculations shows clearly that the charge balance for x/2y > 1 is predominantly achieved by an increase of the Ru valence from Ru(IV) to Ru(V), while Cu remains in the Cu(II) oxidation state. (C) 2002 Elsevier Science B.V. All rights reserved.