Influence of Oxygen Partial Pressure on the Synthesis of Ba sub 2 YCu sub 3 O sub 7 from a Novel Oxalate Precursor.

An oxalate precursor precipitate is prepared by reacting carbonate, hydroxide and/or oxides with oxalic acid in heated aqueous solution. By this approach there are no extraneous anions or cations introduced by the starting salts or created during the reaction since the products are only water and carbon dioxide. Specific solubility differences may be compensated by recycling the filtrate. The thermal conversion of the resulting coarse crystalline precipitate to the desired oxide product is studied by thermoanalytical techniques and x-ray diffraction. Consequently, the kinetics of the final stage of the reaction, eq. 1, are influenced by the value of x. The oxygen content and, hence, the defect structure of the product depends upon the partial pressure of oxygen and the temperature. 2BaCO sub 3 + 1/2Y sub 2 O sub 3 + 3CuO -> Ba sub 2 YCu sub 3 O sub x + 6.5-x over 2 O sub 2 + 2CO sub 2.