Crystal Structure of Pb_2Sr_2MCu_3O_<8+δ> System (M=Nd,Sm, Eu, Gd, Dy, Y_<1-x>Ca_x, Ho and Er)

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The crystal structure of Pb.Sr.MCu,0. (M=Nd, Sm, Eu, Gd, Dy, Y,-..Ca..., Hoand Er) has been analyzed by the Rietveld method of X-ray powder diffraction data.In order to best fit the data several structural models with the different space groupshave been tried. Amgng them the two models with the space groups of Cmmm andP22.2 in which the oxygen atoms on the Pb0 sheet are displaced along the #-axisfrom the midposition between Pb atoms within the PbO sheet gave the best results. Itis shown that the lattice parameters and the interatomic distances vary with the ionicradius of lanthanoides. The systematic variation of the atomic arrangement in theunit cell which consists of stacking of sheets having a different role is argued in corn-parison with the prototype of the Ba.LnCu..0.., system. The bond lengths of the con-stituent atoms are also argued with special emphasis on the local environment of twocopper sites. In the Pb.Sr.(Y. ...Ca..)Cu.0. system, the interatomic distances changemore largely by Ca-doping than by the effect of the size of the Ianthanoide atoms.[Pb.Sr.LnCu.O., Pb,Sr.(Y.-...Ca...)Cu.O., Rietveld refinement, X-ray powder lj diffraction, ioraic radius, compressibility{
社団法人日本物理学会の論文
1992-03-15