Chemical reduction of LaNi0.5Cu0.5O3: the oxygen deficient perovskite like cupronickelite LaNi0.5Cu0.5O2.25

Abstract

By heating the perovskite type cupronickelate LaNi_0.5Cu_0.5O₃ under flowing H₂ at 250 °C, the reduced cupronickelite LaNi_0.5Cu_0.5O_3−δ has been prepared. TGA data point to an oxygen content equal to 2.25 which is understood in terms of the simultaneous presence of Ni(I) and Cu(II). Electron diffraction gives evidence for a 2a_p√2 × 2a_p√2 × 2a_p perovskite supercell. Assuming that the crystal chemical properties of the isoelectronic 3d⁹ cations Cu²⁺ and Ni⁺ are rather similar, an average structure derived from the ordered perovskite type of the oxygen deficient cuprate La_8−xSr_xCu₈O₂₀ is retained in Rietveld calculations, from neutron powder diffraction data. A two phase model allows the calculation of two sets of Ni/Cu ratios i.e. the compositions LaNi_0.6Cu_0.4O_2.2 and LaNi_0.4Cu_0.6O_2.3 which originate in the parent components of the oxidized pseudo solid solution. The basic structural trends of the Ni(Cu) rich phase are connected to a strong preference of Ni⁺ for square and octahedral coordination and Cu²⁺ for pentagonal pyramidal coordination.