Perovskite-like intergrowth structure of the reduced cuprate Nd2CuO3.5: a combination of defect and excess oxygen non-stoichiometry phenomena

The structure of the cuprate Nd2CuO3.5, prepared by hydrogen reduction of Nd2CuO4 at 290 °C, is reported. The oxygen non-stoichiometry, deduced from X-ray powder diffraction calculations, points to the simultaneous existence of defect and excess phenomena, up to now known only separately, as in Sr2CuO3 and LaSrNiO3.1(oxygen defect) and La2NiO4.18(oxygen excess). Special emphasis is devoted to the neodymium oxygen slab whose composition is modelled in terms of the as-calculated formula NdO0.9/O0.6/NdO0.9. The structure of such slabs combines the crystal chemical trends of NaCl and fluorite as observed in the K2NiF4 and Nd2CuO4 structures, respectively.