Hermann Scheler

Synthesis and properties of compounds in the system Sr2CuO3−Ca2CuO3

The ternary compounds Ca 2 CuO 3 , Sr 2 CuO 3 , and their solid solution Sr 2− x Ca x CuO 3 have been prepared by the decomposition of coprecipitated oxalates and/or by conventional solid state reaction. Both reaction methods are compared. The obtained compounds crystallize in the orthorhombic system. The lattice constants were determined, and the formation of solid solution crystals over the whole range of composition was obtained. The compounds were characterized concerning their thermal stability and their decomposition in moist air. Thermogravimetric, X ray, and vapor pressure measurement show that the compounds are of a very slight variation in oxygen stoichiometry. First measurements of the specific heat and IR spectra are discussed.

Preparation of YBa2Cu3O7−x by thermal decomposition of coprecipitated oxalates

Yttrium, barium and copper oxalates are coprecipitated quantitatively from metal acetate solutions with oxalic acid in water-acetone mixtures. The particle-size distribution of the precipitate can be controlled by the precipitation conditions. Thermal decomposition of the coprecipitate leads to single-phase YBa2Cu3O7-x. Despite the intermediate formation of BaCO3, the minimal reaction temperature (770 °C) is clearly lower than that for the solid-state reaction. Results of differential thermal analysis and isothermal thermogravimetry are discussed. The products are characterized by X-ray diffraction and infrared spectroscopy.