YBa_<2-x>Sr_xCu_3O_<7-σ>(x=0〜1.2)の結晶構造と超伝導特性

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A systematic study on superconductivity (T_c) and structural parameters of YBa_<2-x>Sr_xCu_3O_<7-σ> (0≦x≦1.2) has been carried out by the Rietveld analysis of X-ray powder diffraction patterns and by measurement of d. c. electrical resistivity. Single phase samples were obtained in the whole range of x = 0-1.0, and Sr atoms were substituted exclusively for the Ba sites in YBa_<2-x>Sr_xCu_3O_<7-σ>. T_c and lattice constants decreased linearly with the increase of x from x = 0 to 1.2 except for x = 1.0. However, a discontinuous raise of T_c and a change in the axial ratio (a/b) was observed at x = 1.0. In this structure the T_c's have obvious relations with, the oxygen occupancy in a Cu-O one dimensional chain as well as Ba (Sr)-O and Y-O length. The oxygen; atoms in this system play an important role in superconductivity. The orthorhombic-tetragonal phase transition in x = 1.0. compound took place at 550 ℃, where the oxygen content was 6.7. The structure of the high temperature phase was refined as tetragonal (P4/mmm) by Rietveld analysis using X-ray powder diffraction patterns at room temperature. The low temperature phase which showed superconductivity was analysed using an orthorhombic structural model. However, we refined the structure using a micro-twin model, which fitted the observed diffraction patterns much better than the single phase model.
社団法人日本セラミックス協会の論文
1990-02-01