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

Two co-doped high-Tc superconducting systems, YBa2−xLaxCu3−xAlxOz and YBa2−xLaxCu3−xZnxOz (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 YBa2Cu3−xAlxOz and YBa2Cu3−xZnxOz, it shows that in the Al-single-doped YBCO system, the depression of the critical temperature (Tc) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the Tc 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 CuO2 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.

► YBa2−xLaxCu3−xMxOz (M = Al, Zn) are synthesized and investigated for the first time.
► A comparative study with two corresponding single-doped Y-123 systems is made.
► La impurity blocks the process of orthorhombic–tetragonal transition.
► The structural parameter [Cu(2)–Ba]z has a dominating influence on the HTSC.
► La doping improves the solid solubility of YBa2Cu3−xMxOz (M = Al or Zn) system.