YBa_<2-x>Sr_xCu_3O_<7-d>における酸素の無秩序化と電荷移動効果 Oxygen Disordering and Charge Transfer Effect in YBa_<2-x>Sr_xCu_3O_<7-d>
We have investigated neutron powder diffraction of YBa<SUB>2-x</SUB>Sr<SUB>x</SUB>Cu<SUB>3</SUB>O<SUB>7-d</SUB> with x=0, 0.4, 0.8 and 1. Their Rietveld analyses were carried out in space group Pmmm assuming two different disordering models: Model A where the O(1) is displaced from (0, 1/2, 0) to (x, 1/2, 0) so that each alternate chain has some kind of zig-zag chain and Model B where the available oxygen atoms are located at both the O(1) and 0(5) sites to give full and empty Cu-0 chains along the a-axis. The refinements based on model B have revealed that substitution of Sr for Ba causes an increase of isotropic temperature factor for the O(1), indicating an increasing in local oxygen disordering. This disordering in the model B is consistent with the Raman results that the defect induced mode gains intensity with increasing Sr content. A possible picture of the slight decrease of T<SUB>c</SUB> in YBa<SUB>2-x</SUB>Sr<SUB>x</SUB>Cu<SUB>3</SUB>O<SUB>7-d</SUB> is discussed in terms of both local oxygen disordering and associated charge-transfer effect.
粉体および粉末冶金 43(2), 195-199, 1996-02-15
Japan Society of Powder and Powder Metallurgy