Extra oxygen in electron superconductors: Ce and Th doped Nd₂CuO_4+δ and Gd₂CuO_4+δ

Using iodometric titration techniques, we have systematically studied the oxygen content of the title compounds. Our oxidized and reduced samples both show an excess of oxygen above the nominal value of 4. This extra oxygen tends to partially compensate the effect of the tetravalent cation doping and must be considered for a complete understanding of the doping of electron superconductors. The partial removal of some of this extra oxygen is presumably the reason for the necessity of a reduction step in the preparation of electron superconductors. In the case of our Ce doped Gd2CuO4 samples, there is an especially high concentration of extra oxygen and we are unable to make them superconducting. © 1989.