STUDY OF APICAL OXYGEN-ATOMS IN A SPIN-LADDER CUPRATE COMPOUND BY X-RAY-ABSORPTION SPECTROSCOPY NEAR THE CU-K-EDGE

The structure of high-T-c superconducting cuprate compounds is based o n CuO2 planes alternating with blocks that behave as charge reservoirs . The apical oxygen atoms which belong to these reservoirs are suspect ed to play a role in the mechanism of superconductivity. It thus seems necessary to measure the amount of apical oxygen atoms in various com pounds, as a function of the superconducting properties. Polarisation dependent X-ray absorption spectroscopy (XAS) measurements were perfor med near the Cu K-edge on three types of phases. We collected informat ion about the neighbourhood of the copper atom in the cuprate planes a nd in the direction perpendicular to these planes. Two of these phases have well known structures: Bi2212 in which copper atoms are on a pyr amidal site and infinite layer phase, a square planar cuprate without apical oxygen. We used the obtained results as reference data to study a new copper-rich phase related to the spin-ladder series.