Neutron Structural Studies of Superconducting Bi_2Sr_2CuO_<〜6> and Bi_<2-x>Pb_xSr_<1.8>La_<0.2>CuO_<6+δ>(x=0.0 and 0.2)

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We have investigated the influence of incorporation of La- and Pb-ions on the structural features of Bi-2201 system by Rietveld refinement of the neutron diffraction patterns of samples with three different compositions, viz. (A) Bi_2Sr_2CuO_<〜6> with T^<R=0>_c=9.5 K; (B) Bi_2Sr_<1.8>La_<0.2>CuO_<6+δ> with T^<R=0_c=16.5 K; and (C) Bi_<1.8>Pb_<0.2>Sr_<1.8>La_<0.2>CuO_<6+δ> with T^<R=0>_c=21 K. The large fraction of vacancies observed at Bi-, Sr-, Cu- and O(2)-sites in the sample A get filled up on substitution of La in the sample B. However, these vacancies reappear to a smaller extent for the sample C. The O(3)-ions belonging to the Bi-double layer are found to be disordered for all the three samples, though the nature of the disorder is highly sensitive to the type of substitution. A correlation exists between bond valence of the Cu-sites and the measured T_c-value of the three samples.
社団法人応用物理学会の論文
1993-04-15