STUDY OF CU ABSORPTION-EDGE OF YBCO SUPERCONDUCTOR BY X-RAY-POWDER DIFFRACTION METHOD

Using synchrotron radiation, we carried out X-ray powder diffraction o f the YBa2Cu3Oy compounds at the several points near the Cu K absorpti on edge. From the Rietveld analysis of these data, we obtained the ano malous X-ray atomic scattering factor of the Cu ions in the Cu(1) and Cu(2) sites in the superconductor (y = 6.90) and the nonsuperconductor (y = 6.07). In both compounds, the absorption edge of the Cu ions in the Cu(1) and Cu(2) sites is nearly equal to that of CuO. The results indicate that changes in the O content of YBa2Cu3Oy produce no signifi cant changes in the valence state of Cu ions in the Cu(1) and Cu(2) si tes. Detailed inspection of the spectra, however, shows that the energ y position of the edge of the Cu(1) sites in the nonsuperconductor is a little lower than in the superconductor, but the magnitude of the sh ift is not large as that expected from monovalent Cu ion.