SYNTHESIS OF SUPERCONDUCTING SR2CUO3+DELTA USING HIGH-PRESSURE TECHNIQUES

The synthetic conditions of the ''Sr2CuO3+delta'' phase (''214'') in the Sr-Cu-O system were investigated using high-pressure techniques at 5 GPa and 1400-degrees-C. Sr2CuO3 powder was used as starting materials, and KClO3 as oxidizer. The effect of the initial amount of KC103 on the structure and the physical properties was investigated. We observed two crystallographic domains of the tetragonal fundamental structure: a almost-equal-to 3.76 angstrom, c almost-equal-to 12.54 angstrom, and a almost-equal-to 3.79 angstrom, c almost-equal-to 12.46 angstrom, respectively. TEM investigations of the latter have shown evidence of modulations along the [110] direction which lead to a new superlattice with periodicity of 5a/square-root 2x5a/square-root 2Xc. Moreover, two new phases appear in this system; one is monoclinic and related to the infinite layer structure with a=8.430 (1) angstrom, b=11.100 (1) angstrom, c=3.641 (1) angstrom, beta=83.2-degrees, the other suggests a change of the space group from body centered (I) to primary (P). The electrical properties and magnetic behavior observed for these materials are discussed in relation with the synthesis conditions and observed phases. Bulk superconductivity up to 80 K has been obtained.