Structure and superconducting properties of YBa2−xLnxCu3O7±δ (Ln = La, Nd or Gd) and (Ln,Ln′) 3−xBa3+xCu6O14+δ

In YBa2−xLnxCu3O7±δ (Ln = La, Nd or Gd), the structure becomes tetragonal with increase in x and the TC of the orthorhombic phase decreases with x. Members of (Ln,Ln′) 3−xBa3+xCu6O14+δ (Ln = Nd or Gd) are generally tetragonal and non superconducting. Ln3Ba3Cu6O14+δ and LnBa2Cu3O7±δ (Ln = Nd or Gd) prepared by low-temperature decomposition of nitrates are also tetragonal and nonsuperconducting. Random occupation of Ba in LnBa2Cu3O7±δ or La3Ba3Cu6O14+δ appears to favour the tetragonal structure. Furthermore oxygen is less labile when La partly substituting Ba in these oxides.