Stoichiometry and copper valence in the Ba1-yCuO2+delta system

The cation stoichiometry and the tunability of oxygen content in the Ba1-yC uO2+delta phase were investigated by means of various methods of chemical a nalysis. Samples with different nominal metal stoichiometries, y(nom) rangi ng from 0 to 0.1, were synthesized. Single-phase samples were obtained for y(nom) approximate to 0.1, i. e. with about 10 mol% barium deficiency. The possibility to stabilize the Ba1-yCuO2+delta phase with different oxygen st oichiometries was studied thermogravimetrically. Under an argon atmosphere below 400 degrees C a part of the excess oxygen of the fully oxygenated Ba0 .9CuO2.01 sample was found to be released in two steps leading to stoichiom etries of Ba0.9CuO1.97 and Ba0.9CuO1.94. On the other hand, above 400 degre es C it was possible to continuously tune the oxygen stoichiometry at least down to Ba0.9CuO1.85 (700 degrees C). A decrease in the copper valence wit h decreasing oxygen content led to an increase in the effective magnetic mo ment obtained from the magnetic susceptibility measurements performed for t wo Ba0.9CuO2+delta samples with different oxygen stoichiometries.