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

Abstract

The structure of the cuprate Nd₂CuO_3.5, 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 LaSrNiO_3.1(oxygen defect) and La₂NiO_4.18(oxygen excess). Special emphasis is devoted to the neodymium oxygen slab whose composition is modelled in terms of the as-calculated formula NdO_0.9/O_0.6/NdO_0.9. The structure of such slabs combines the crystal chemical trends of NaCl and fluorite as observed in the K₂NiF₄ and Nd₂CuO₄ structures, respectively.