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

Abstract

Structural changes related to changes in the oxygen stoichiometry 2 + δ in the mixed-valent cuprate ‘BaCuO _{2 + δ} ’ have been studied by means of X-ray and neutron powder diffraction techniques. The cubic structure of ‘BaCuO _{2 + δ} ’ with space group Im3m consists of partially and fully occupied parts with metal atoms in several different crystallographically equivalent positions. Three samples with stoichiometries of Ba _0.9 CuO _2.02 ·(CO ₂ ) _x , Ba _0.9 CuO _1.93 ·(CO ₂ ) _x and Ba _0.9 CuO _1.86 ·(CO ₂ ) _x were studied and the structures were found to differ in terms of the occupancies of two crystallographic positions of oxygen. This conclusion correlates with thermogravimetric data obtained for the same samples in an argon atmosphere since upon heating, oxygen evolution from the fully oxygenated sample was found to occur in two distinct steps.