Structure ofYBa2Cu3O7−δversus temperature by x-ray-absorption spectroscopy (original) (raw)

We present extended x-ray-absorption fine-structure data on YBa2Cu307taken at four temperatures: 80, 112, 170, and 297 K. Spectra from both the Y edge and Cu edge are analyzed for the mean distances to near neighbors and the mean-square relative displacements o.. The distances show little temperature dependence. The o. 's are unusual because they vary more strongly at low temperature (80-110 K) than at high temperature (170-300 K). This could indicate some softening of the bond strengths near 170 K which may entail a subtle structural change. From a study of the Cu E edge we conclude that the x-ray-absorption near-edge structure (XANES) does not provide evidence for the existence of Cu(III) in YBa2Cu307s. We find that a peak at-9002 eV in the XANES, the origin of which has been the subject of conflicting opinions in La2 "Sr Cu04~, is associated with interference effects in Cu(II) complexes and its presence is not evidence for Cu(III) in YBa2Cu307-$.