Structural and superconducting properties of co-doped YBa2−xLaxCu3−xMxOz and La-free YBa2Cu3−xMxOz (M = Al, Zn) high-TC superconductors

Abstract Two co-doped high- T c superconducting systems, YBa 2− x La x Cu 3− x Al x O z and YBa 2− x La x Cu 3− x Zn x O z (0 ⩽  x  ⩽ 0.3), both of which have not been reported up to the present, were synthesized. The structural and superconducting properties have been investigated by X-ray diffraction (XRD) and DC magnetization measurement. Comparing the properties of these co-doped systems with single-doped systems YBa 2 Cu 3− x Al x O z and YBa 2 Cu 3− x Zn x O z , it shows that in the Al-single-doped YBCO system, the depression of the critical temperature ( T c ) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the T c descends slower than that in (La, Zn)-co-doped system. This is possibly due to the opposite change of the distance between the Ba site and the CuO 2 plane induced by the La doping. Besides, the La doping has another effect of improving the solid solubility compared with the Al- or Zn-single-doped system.