SOFT-X-RAY-ABSORPTION STUDIES OF TL2BA2CA2CU3O10-DELTA HIGH-TC SUPERCONDUCTORS

X-ray absorption around the oxygen K and the Cu L(III) edge of Tl2Ba2Ca2Cu3O10-delta high-T(c) superconductors with different oxygen content delta, was measured. Near the O 1s edge, three distinct pre-edge peaks with maxima at 528.3, 529.4, and 530.6 eV, respectively, are are revealed. They are ascribed to core-level revealed. They are ascribed to core-level excitations of oxygen 1s electrons to empty states which have predominantly oxygen 2p character, located in CuO2, BaO, and TlO planes, respectively. A strong dependence of T(c) on oxygen hole concentration at O(1) and O(1)' sites in the CuO2 layer is found. Near the Cu 2p3/2 edge, two main peaks are observed. The peak at 931.2 eV is ascribed to a 2p3d10 final state. This implies a predominately Cu2+ ground state which has mainly 3d9 character. The peak at 933 eV is ascribed to a 2p3d10L final state. This peak shows an intensity increase with T(c), i.e., with ligand hole concentration, and is believed to arise from a formally Cu3+ ground state which has mainly 3d9L character. No evidence of a monovalent (Cu1+) 3d10 ground state was found.