Comparison of Superconductivity and Structure for Lanthanum Replacing for Barium and Copper in YBa2Cu3Od

X-ray diffraction studies and the resistivity measurements are used to characterize the structure and the superconductivity of the nominal composition of YBa₂Cu_{3 – x} La _x O _d (YBCLO) cuprates with x 0.30. There was a BaCuO₂ impurity phase detected with x 0.10. The structure of the main phase (123) has the orthorhombic form with Pmmm symmetry in the whole doping range. With increasing content of lanthanum, x, the lattice constants increase for x < 0.04, and decrease for x 0.04. Rietveld refinements for X-ray diffraction show that the dopant of lanthanum substitutes for copper in the lower doping level, and replaces for both barium and copper in the high doping level. The zero-resistance temperature T _c0 first increases with the increase of the content of lanthanum in YBCLO as x 0.04 and then decreases with x as x 0.04. We compared the results with those of La-doped YBa_{2 – z} La _z Cu₃O _y cuprates. The different relationship in superconductivity dependence of lanthanum content may result from the strains due to the different occupancy of lanthanum in the unit cell of YBa₂Cu₃O _d .