Enlargement of the stability range and superconducting domain of the T/O type phase of the La2)CuO4-Nd2CuO4 system after treatment under oxygen pressure

Two main solid solutions exist in the La(2)CuO(4)-Nd(Z)CuO(4) system. The structure of the first one is related to that of tetragonal K(2)NiF(4) and is labelled as T/O; copper ions are in sixfold coordination (elongated octahedron), The second one has an original structure, called T′, in which copper ions are in square planar coordination. When synthezised in air at 800°C, the upper limit of the T/O type solid solution is 0.55. By subsequent treatment under 40 MPa oxygen pressure between 920 and 94O°C, this limit is shifted up to ≃ 0.80, and an ultimate oxidation by electrochemistry induces a bulk superconductivity, as in the case of normaly prepared T/O phases (x ≥ 0.55). Data are given on the change in the unit cell parameters, deviation from oxygen stoichiometry and conduction properties consecutive to the oxidizing treatments.