Improved synthesis of ceramic superconductors with alkaline earth peroxides

Results are reported on a synthesis and processing study of Ba/sub 2/YCu/sub 3/O/sub 7-x/. Solid-state syntheses using BaO/sub 2/ and BaCO/sub 3/ are compared. BaO/sub 2/ routinely produces more homogeneous, denser and more metallic material as determined by EDXS, x-ray diffraction, SEM, and d.c. resistivity. C-axis alignment was observed when loose powders were fired at temperatures > 9250C and is thought to occur because of unfaceted, mass transport limited a-b plane growth. To limit intergrain BaCO/sub 3/, a source of J/sub c/ reduction, Ba/sub 2/YCu/sub 3/O/sub 7-x/ was prepared in flowing N/sub 2/ using BaO/sub 2/. Orthorhombic single phase (x-ray diffraction: a = 3.83 A, b = 3.89 A, c = 11.69 A) material was obtained. Material made in O/sub 2/ under the same conditions shows identical weight loss and oxygen stoichiometry (6.8) as estimated by lattice parameters. BaCO/sub 3/ produced material reached 6.8 after extended reaction in O/sub 2/ (> 32 hours) but on 6.5 in low rates of N/sub 2/. A 25% reduction in intergrain BaCO/sub 3/ was achieved, but total inert handling is needed for further improvements. Relevant aspects of peroxide chemistry and potential applications of this process are discussed