Synthesis of Ba2YCu4O8 by anionic oxidation-reduction

The superconducting phase Ba2YCu4O8 has been synthesized (as a bulk powder) in flowing oxygen. This was achieved by using the anionic oxidation/reduction method (or the SCD method), in which an aqueous solution containing oxidizing (NO-3 salts) and reducing components (e.g., acetate salts) is spray dried into an intimate mixture. At 300 degree C, 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 phase can subsequently be produced at lower temperatures and shorter reaction times. Using this method, ∼93--94% phase pure Ba2YCu4O8 (as determined by x-ray diffraction) has been synthesized in flowing oxygen. Pellets of Ba2YCu4O8 fabricated from the mixed oxides were prepared and partially sintered by firing at 800 degree C in flowing oxygen for 50 hours. Resistivity and magnetic (A.C.) susceptibility measurements show onset Tc's of 82--84 and 72--73 K, respectively