SYNTHESIS OF YBA2CU3O6+X FROM COPRECIPITATED HYDROXIDES

Superconducting YBa2Cu3)6+x was synthesized by decomposition of coprecipitated hydroxides. Phase crystallization occurs with formation of intermediate phases Ba2Cu3O6+x and Y2O3. In argon atmosphere, single submicrometer phase is obtained at temperatures as low as 700-degrees-C. In oxygen, a pure phase is obtained only at 800-degrees-C. X-ray analysis indicates tetragonal structure although it corresponds to oxygen composition x = 0.7. This is caused by microtwins in the (a, c) plane. Further annealing at higher temperatures transforms the material to orthorhombic material with twins in the (a, b) planes. Nitrates in the precipitate induces preferred crystallization of the 124 phase after heat treatment under oxygen at 750-degrees-C. Transport and magnetic properties are discussed as a function of the microstructure.