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 char acterize the structure and the superconductivity of the nominal composition of YBa2Cu3-xLaxOd (YBCLO) cuprates with x less than or equal to 0.30. Ther e was a BaCuO2 impurity phase detected with x less than or equal to 0.10. T he 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 <greater than or equal to> 0.04. Rietveld refinements for X-ray diffraction show tha t 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 conte nt of lanthanum in YBCLO as x less than or equal to 0.04 and then decreases with x as x greater than or equal to 0.04. We compared the results with th ose of La-doped YBa2-zLazCu3Oy cuprates. The different relationship in supe rconductivity dependence of lanthanum content may result from the strains d ue to the different occupancy of lanthanum in the unit cell of YBa2Cu3Od.