CRYSTALLIZATION OF HIGH-TEMPERATURE SUPERCONDUCTORS FROM NONSTOICHIOMETRIC MELTS

Crystallization of high-temperature superconductors YBa//2Cu//3O//6//. //5// plus //x and (La,Sr)//2CuO//4// minus //y from homogeneous nonstoichiometric melts has been studied. The phase diagram of the CuO-BaO system was constructed. The real phase diagram of the CuO-BaO system in air having the complete liquidus corresponds to the superposition of two phase diagrams - those of the CuO-BaO and the CuO//0//. //5-BaO systems. An important part in the process of the formation of superconducting crystals is played by Cu** plus cations. The formation of peroxide oxygen pairs O//2**2** minus bound to Ba is briefly considered. Platelet-like YBa//2Cu//3O//6//. //5// plus //x crystals 8 multiplied by 8 multiplied by 0. 1 mm**3 in size and prismatic La//2// minus //xSr//xCuO//4// minus //y crystals 6 multiplied by 4 multiplied by 10 mm**3 in size were synthesized by the method of spontaneous crystallization from homogenized nonstoichiometric melts enriched with copper oxides. La//2// minus //xSr//xCuO//4// minus //y single crystals 8 multiplied by 8 multiplied by 12 mm**3 in size were grown on a seed from homogenized nonstoichiometric melts by the Czochralski technique. The measurements on annealed YBa//2Cu//3O//6//. //5// plus //x single crystals yielded: T//c equals 93 K, TRIAN OP T approximately equals 0. 2 K.