Effect of rare-earth ion size on local electron structure in RBa2Cu3O7-delta (R = Tm, Dy, Gd, Eu, Nd and Y) superconductors: A positron study

摘要

The effects of rarc-earth ionic size on the local electron structure, lattice parameters and superconductivity have been investigated by positron annihilation technique (PAT) and related experiments for RBa2Cu3O7-delta (R = Tm, Dy, Gd, Eu, Nd and Y) superconductors. The local electron density ne is evaluated as a function of the rare-earth radius. The results show that both the bulk-lifetime tau(B) and the defect lifetime tau(2) increase with increasing rare-earth ionic radius, while the local electron density n(e) decrease with increasing rare-earth ionic radius. These results prove that the changes of n(e), the degree of orthorhombic distortion and the coupling between the Cu-O chains and the CuO2 planes all have an effect on the superconductivity of RBa2Cu3O7-delta systems. (c) 2005 Elsevier B.V. All rights reserved.