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

The effects of rare-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−δ (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 τB and the defect lifetime τ2 increase with increasing rare-earth ionic radius, while the local electron density ne decrease with increasing rare-earth ionic radius. These results prove that the changes of ne, 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−δ systems.