THE PHASE-STABILITY DIAGRAMS FOR THE SYSTEMS ND2CUO4-DELTA AND ND1.85CE0.15CUO4-DELTA

The dependences of the degrees of oxygen nonstoichiometry in Nd2CuO4-delta and Nd1.85Ce0.15CuO4-delta on temperature and oxygen pressure have been determined by thermogravimetric measurements in the range of temperature 350-950-degrees-C and the range of oxygen pressure 10(-5)-1 atm. The nature of the decomposition of these oxides in the range of oxygen pressure 10(-5)-1 atm has been determined by thermogravimetric analysis and X-ray diffraction. In the solid state, decreasing oxygen pressure causes Nd2CuO4-delta to decompose to NdCuO2+Nd2O3 and then to Nd2O3+Cu2O. The solid solution Nd1.85Ce0.15CuO4-delta decomposes to Nd2O3+NdCeO3.5+Cu2O. The solidus line of incongruent melting has been determined in the range of oxygen partial pressure 10(-6)-1 atm by differential thermal analysis and the phases formed on solidification have been identified by X-ray diffraction. The phase stability diagrams for Nd2CuO4-delta and Nd1.85Ce0.15CuO4-delta have been constructed. The dependence of the onset of superconductivity in Nd1.85Ce0.15CuO4-delta on the oxygen pressure and temperature at which the specimen was annealed, and hence on the oxygen nonstoichiometry, has been determined.