Stoichiometry and copper valence in the Ba1–yCuO2+δ system

Abstract

The cation stoichiometry and the tunability of oxygen content in the Ba _1–y CuO _2+δ phase were investigated by means of various methods of chemical analysis. Samples with different nominal metal stoichiometries, y _nom ranging from 0 to 0.1, were synthesized. Single-phase samples were obtained for y _nom ≈0.1, i.e. with about 10 mol% barium deficiency. The possibility to stabilize the Ba _1–y CuO _2+δ phase with different oxygen stoichiometries was studied thermogravimetrically. Under an argon atmosphere below 400 °C a part of the excess oxygen of the fully oxygenated Ba _0.9 CuO _2.01 sample was found to be released in two steps leading to stoichiometries of Ba _0.9 CuO _1.97 and Ba _0.9 CuO _1.94 . On the other hand, above 400 °C it was possible to continuously tune the oxygen stoichiometry at least down to Ba _0.9 CuO _1.85 (700 °C). A decrease in the copper valence with decreasing oxygen content led to an increase in the effective magnetic moment obtained from the magnetic susceptibility measurements performed for two Ba _0.9 CuO _2+δ samples with different oxygen stoichiometries.