SYNTHESIS OF BA2YCU3O7 BY THE SCD METHOD USING AMINO-ACID SALT REDUCING AGENTS

The anionic oxidation-reduction or SCD method relies on an internal oxidation-reduction reaction which converts spray-dried precursors into intimately mixed and highly reactive metal oxide powders. Earlier studies focused on precursor mixtures containing oxidizing components such as NO-3 salts with reducing salts (RCOO-, where R is H, CH3, or CH2CH3) which react to form Ba2YCu3O7 powder. In this work, amino acid reducing agents are used. The impact of the functional group change, in the reducing agent of the NO-3 amino acid precursors, is shown by DSC to result in sharp (and therefore rapid) oxidation-reduction reactions which occur at lower temperatures. The trend in reaction temperature correlates inversely with the expected basicity of the amino group in the series (numbers in parentheses represent mole ratios): CH3CH(NH2)COO- NO-3 ( 4 9) = 206°C > NH2CH2COO- NO-3 ( 4 9) = 195°C > NH2CH2CH2COO- NO-3 ( 4 9) = 191°C. The mixed oxide product is highly reactive and can be converted to single-phase Ba2YCu3Ox when fired at 900-910°C for 10 min in flowing oxygen. © 1990.