Thermogravimetric measurements of the equilibrium oxygen partial pressure (
) as a function of the oxygen contenty were performed on Nd1.85Ce0.15Cu1+δOy samples with controlled Cu contents (1+δ=1.00, 1.01 and 1.02) at 1173 and 1237 K. The data obtained showed a dependence of the oxygen non-stoichiometry on the nominal Cu content. These measurements are discussed in terms of the presence of Cu defects in the T′ structure. The superconducting response of this material in samples with controlled oxygen and Cu contents was also studied. The superconducting response was found to be very sensitive to the presence of small amounts of cationic and anionic defects.