Influence of Gd/Eu Substitution on the Local Electron Density and the Superconductivity of Y1−xRxBa2Cu3O7−δ (R=Gd, Eu) Systems

Abstract

The influences of Gd or Eu substitution on the local electronic density, lattice structure and the superconductivity are systemically studied by means of positron annihilation technique (PAT) and x‐ray diffraction (XRD) for Y1−xRxBa2Cu3O7−δ (R=Gd, Eu; x=0.0, 0.2, 0.5, 1.0) systems. XRD results show that all of the Y1−xRxBa2Cu3O7−δ samples have an orthorhombic phase as same as YBa2Cu3O7−δ (YBCO) sample. The positron annihilation experiments show that the mean positron lifetime increases with increasing Eu or Gd substitution content. The local electron density ne is evaluated as a function of the substitution content. The results indicate that the substitution ions in Y sites not only influence the local electron density around Y ion, but also change the distribution of electron density around Cu‐O chains. 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 Y1−xRxBa2Cu3O7...