Structures and Upper Critical Fields of High Tc Superconductors (RE)Ba₂Cu₃Ox

A systematic study of structure and superconductivity of (RE)Ba 2 Cu 3 O x (RE: rare earch) is carried out. All superconducting (RE)Ba 2 Cu 3 O x have oxygen deficient perovskite structure. As the ion radius of the RE ion increases, lattice parameters increase and the orthorhombic distortion becomes smaller. Superconducting transition temperature is lower for (RE)Ba 2 Cu 3 O x with smaller RE ion radius. Upper critical fields ( H c2 ) are measured resistively up to 90 kOe. All superconducting (RE)Ba 2 Cu 3 O x have similar values of d H c2 /d T | T c to that of YBa 2 Cu 3 O x . The estimated H c2 at absolute zero ranges from 1250 kOe to 1850 kOe.