Neutron powder diffraction study on Eu-substituted Bi₂Sr₂CaCu₂O_8+y high temperature superconductor

We have used a neutron powder diffraction method to study the structural changes in the Bi₂Sr₂Ca_1−xEu_xCu₂O_8+y compound caused by the partial substitution of Ca by Eu. Besides the systematic variation of the parameters of the orthorhombic 5.4 ÅX5.4 ÅX30.7 Å sub-cell, we observed atomic rearrangement in the BiO-layer and modifications in the square-pyramidal coordination polyhedra of the Cu ion. The onset temperature T_onset as determined by the AC susceptibility method has a broad maximum at x = 0.3, and no superconductivity is observed at x = 0.6 in the temperature range T > 4.2 K. We discuss also about the reasons for the broadening of the transition range and the decrease of the Meissner fraction concomitant to the increase of the Eu concentration.