Abstract
A nonstoichiometric structure of Nd 1+ x Ba 2− x Cu 3O 7− z has been refined by Rietveld analysis of neutron powder diffraction data. A Ba site is substituted partially by Nd atoms, which causes a decrease of hole carriers on a CuO 2 plane and lowers T c. T c recovers again with increasing content of oxygen introduced by high-pressure oxygen annealing. A modulated structure in Bi 2(Sr, Ca) 3Cu 2O 8+z has been clarified by simultaneous Rietveld refinement of neutron and X-ray powder diffraction data. It is shown that the modulated structure is resulted from excess oxygen atoms incorporated in a Bi-O layer.
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