Structural changes related to changes in oxygen stoichiometry in the Ba1-yCuO2+delta center dot(CO2)(x) system as determined by powder X-ray and neutron diffraction

Structural changes related to changes in the oxygen stoichiometry 2+delta i n the mixed-valent cuprate 'BaCuO2+delta' have been studied by means of X-r ay and neutron powder diffraction techniques. The cubic structure of 'BaCuO 2+delta' with space group Im3m consists of partially and fully occupied par ts with metal atoms in several different crystallographically equivalent po sitions. Three samples with stoichiometries of Ba0.9CuO2.02.(CO2)(x), Ba0.9 CuO1.93.(CO2)(x) and Ba0.9CuO1.86.(CO2)(x) were studied and the structures were found to differ in terms of the occupancies of two crystallographic po sitions of oxygen. This conclusion correlates with thermogravimetric data o btained for the same samples in an argon atmosphere since upon heating, oxy gen evolution from the fully oxygenated sample was found to occur in two di stinct steps.