Structure and superconductivity of Y (Ba1−xRx)2Cu3O7−δ (R=La, Pr, and Nd)

Abstract

Powder X-ray diffraction and electrical-resistivity measurement were used to study the structure and the Tc variation of Y(Ba1−xRx)2Cu3O7−δ(0≤x≤0.2; R=La, Pr, and Nd). The solubility limit was estimated as x=0.05, 0.075, and >0.2 with R=Nd, Pr, and La, respectively, which depends on the ionic radius of dopants. All three series undergo an orthorhombic-to-tetragonal transition at x≈0.15-0.2. Meanwhile, the Tc increases slightly through a maximum at x≈0.025; then decreases rapidly with x, indicating an overdoped system for YBa2Cu3O7−δ. Whereas, the normal-state resistivity increases with x for all temperature ranges. The similarities and differences with various dopants are discussed in conjunction with ionic size, valence change and hole-filling mechanism.