Neutron and X-ray Investigations on the Oxigen Bonding in YBa2Cu30(7-x) combined with Physico-chemical Methods

The occupancy of the oxygen lattice positions at different annealing conditions in Yba2Cu3O(7-x) were determined by Rietveld refinements using neutron and X-ray diffraction data. The occupation density for the oxygen positions O1 to O4 were ascertained. The values of the oxygen content of the samples from this method were compared with those measured by thermoanalysis. The O1 and O4 oxygen atoms are exchangeable by thermal treatment. The oxygen in the planes is fixed and cannot be removed by thermal treatment up to 935oC. The binding strength of O1 in the lattice is stronger than that of O4 atoms; this is demonstrated by a higher temperature of dissociation of the O1 atoms. The amount of the oxygen taken up is not exactly equal to the oxygen actually in the lattice positions. In the temperature region below 400oC adsorption and chemisorption processes become dominant.