Oxygen intercalation of two polymorphs of CuScO2

Both the 2H and 3R'forms of CuScO2 have been intercalated with oxygen to yield CuScO2+x, phases where x has been observed to range from 0.0 to 0.12 and 0.44 to 0.5. The position of the interstitial oxygen in the CuScO2.5 phases was determined from powder neutron diffraction data. In both cases the interstitial oxygen resides in triangular sites in the Cu layer. However, in the 3R form the oxygen is displaced 0.3 Angstrom toward a Sc atom above or. below the Cu plane. When heating the 2H form of CuScO2 under oxygen, the oxygen initially absorbed is released at, about 440 degreesC. The 3R form does not lose oxygen under these conditions but it does lose oxygen around 580 degreesC when heated in air. These are exceptionally low temperatures for the thermal reduction of Cu2+ to Cu1+ in an oxide system, but it is consistent with the low calculated bond valence sum of 1.7 for interstitial oxygen compared to 2.0 calculated for-the network oxygen. The weak bond formed between the interstitial oxygen and Sc in 3R CuScO2 is presumably the reason why this oxygen is more strongly held in the 3R form relative to the 2H form. On oxygen intercalation there is a 1.46% increase of the hexagonal a cell edge the 2H form and a 1.61% increase for the 3R form. The c cell edge expands by 0.23% on oxidation of the 2H form, but contracts by 0.30% on oxidation of the 3R form. This contraction of c and greater expansion for a for the 3R form can be attributed to the weak bond formed between Sc and the interstitial oxygen. Most synthesis routes to CuScO2 give a mixture of the 2H and 3R forms, and this mixing can extend to the atomic level in the form of stacking faults. (C) 2004 Elsevier SAS. All rights reserved.