InCuO_2.5 and ScCuO_2.5: New oxidized copper delafossites with triangular lattices of Cu²⁺ cations

New oxidized delafossite compounds of composition InCuO_2.5 and ScCuO_2.5 are synthesized and their structures are characterized by means of x-ray and neutron powder diffraction. Oxygen intake is accompanied by a small increase of the unit cell, and a complex superstructure attributed to oxygen ordering appears. Average structure refinements show the presence of additional oxygen close to the centres of Cu triangles, and an average copper valence of +2. The two compounds appear to be isostructural. Magnetic measurements show a non-linear thermal increase of the inverse magnetic susceptibility up to some maximum, soon followed by a minimum around 280 K.