Synthesis of Ba sub 2 YCu sub 4 O sub 8 by Anionic Oxidation- Reduction.

The superconducting phase Ba sub 2 YCu sub 4 O sub 8 has been synthesized (as a bulk powder) in flowing oxygen. This was achieved by using the anionic oxidation/reduction method (or the SCD method), sup 1 in which an aqueous solution containing oxidizing (NO sub 3 sup - salts) and reducing components (e. g., acetate salts) is spray dried into an intimate mixture. At300C, an internal exothermic oxidation/reduction reaction completely converts the spray dried powder into the corresponding mixed oxides in one reaction step. Because the resultant mixed oxide powder is homogeneous on a fine scale, the final oxide product can be produced at lower temperatures and shorter reaction times. Using this method, ~93-94% phase pure Ba sub 2 YCu sub 4 O sub 8 (as determined by X-ray diffraction) has been synthesized in flowing oxygen. Pellets of Ba sub 2 YCu sub 4 O sub 8 fabricated from the mixed oxides were partially sintered by firing at 800C in flowing oxygen for 50 hours. Resistivity and magnetic (a.c.) susceptibility measurements shoe onset T sub c 's of 82-84 and 72-73K, respectively.