Polymerized complex synthesis of pure high-temperature superconducting oxides

A novel "polymerized complex" technique has been developed to produce high-pure copper based high-T_c superconductors. The polymerized complex technique is based on the formation of a polymer resin precursor with various metal ions, which can be uniformly distributed in the polymer network keeping their initial stoichiometric ratio. The technique includes four important major steps: (1) formation of stable carboxylate complexes uniformly dispersed into ethyleneglycol, (2) fabrication of polymerized complexes which are formed through dehydration among the hydroxyl groups of ethyleneglycol and the carboxylic acid groups, (3) heating of the polymerized complex resin at moderate temperatures (around 350 °C), which brings about a partial breakdown of the polymer, and (4) various heat treatments to produce a given ceramic powder. It is likely that low cation mobility in the highly viscous polymer network causes little segregation of various metal ions during the pyrolysis. It is stressed in this paper that the present technique offers more convenient and easier fabrication of high pure and homogeneous ceramic powders compared with other more elaborate preparation procedures based on wet chemical routes. Application of the polymerized complex method is demonstrated on the ceramic synthesis of polycrystalline compounds including solid solutions viz. YBa₂Cu₃O_7-d and YBa₂Cu_3-xCo_xO_7-d. Special emphasis is placed on the outstanding purity of the product, which was examined by various techniques including X-ray diffraction, Raman scattering and complex magnetic susceptibility measurements.