Synthesis of B₂YCu₄O₈ by anionic oxidation-reduction

Abstract

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 °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 Ba₂YCu₄O₄ fabricated from the mixed oxides were prepared and partially sintered by firing at 800 °C in flowing oxygen for 50 h. Resistivity and magnetic (AC) susceptibility measurements show onset T_c's of 82–84 and 72–73 K, respectively.