Neutron diffraction study of YBa 2Cu 2.7Fe 0.3O y

Abstract

In order to investigate the correlation between structural and superconducting properties we used two YBa 2Cu 2.7Fe 0.3O y samples with different oxygen contents, which were treated by a thoughtful procedure. One of them was non-superconductive, and the other a superconductor with T c=35K. Their crystal structures were determined using neutron powder diffraction technique. Rietveld analysis of neutron data showed in both samples Fe ions occupy preferential Cu(1) sites, while the oxygen contents are 7.04 (non-superconducting) and 7.16 (superconducting) respectively. The changes of lattice parameters and interatomic distances in the samples are discussed, and are compared with those of the oxygen-deficient undoped YBa 2Cu 3O 7-δ reported in literature, and this is rather instructive. Some preliminary points stated as follows should get confirmed in a further study. For example, a small oxygen content can cause a considerable expansion of the cell volume in both cases, while this occurred in a rather different way in each case; “stepping up” of O(1) is closely related to superconductivity; the corrugation of CuO 2 plane and other structural parameters appear not to be directly related with superconductivity, and so on. More systematic study along this direction is in progress.