COPPER NONSTOICHIOMETRY AT HIGH-TEMPERATURES IN ND1.85CE0.15CU1+ -DELTA-OY/

Samples of Nd1.85Ce0.15Cu1+/-deltaOy with precise control of Cu conten t were prepared by chemical methods. The superconducting response, mic rostructural features and XRD patterns of samples annealed at T-a = 11 00 degrees C in air were studied as a function of the annealing time. The improvement of the Meissner fraction as the annealing time increas es is related to an increased homogenization of the Ce distribution. T he decrease of the Meissner fraction for larger annealing times is att ributed to the existence of a small Cu nonstoichiometry range in the T ' phase. The possibility of Cu defects in the T' phase is discussed. A pseudobinary (Nd,Ce)(2)O-3-CuO phase diagram including a small region of Cu solubility around the (Nd,Ce)(2)CuO4 compound is proposed.