Apical Cu-O bond in YBa2Cu3O(7-delta) superconductors by XAFS

Careful Cu K-edge X-ray absorption fine structure (XAFS) measurements on oriented powders of YBa2Cu3O(7 - delta) were made as a function of temperature, of delta, T(sub c), method of preparation, and grain size. The XAFS data were analyzed for the Cu(1) - O(4) apical bond distance distribution. All samples indicated evidence for a double-peak in the distribution with a splitting of 0.1 A, with the clearest case for the delta approximately equal to 0 samples occurring for the T(sub c) = 89K 20 microns grain samples and the least clear one for the 5 micron grain T(sub c) = 93K sample. There is no significant temperature dependence of the splitting. Because the XAFS evidence for the splitting depends on a small signal, it is prudent to verify its existence by other independent measurements.