Synthesis of YBa 2Cu 3O 7−γ and YBa 2Cu 4O 8 by aerosol decomposition

Abstract

The synthesis of submicron YBa 2Cu 3O 7−γ (1-2-3) and composite 1-2-3/CuO powders using aerosol decomposition of nitrate solutions and the behavior of those powders during subsequent processing were investigated. Transmission Electron Microscopy (TEM) revealed that 1-2-3 and 1-2-3/CuO particles produced at 800°C (residence time of 15 s) were polycrystalline and hollow, while solid particles were produced at temperatures greater than 900°C. Solvent evaporation led to a hollow particle morphology which was retained unless the reactor temperature exceeded 900°C, where densification was rapid enough to result in collapse of the hollow particles within the reactor residence time. Single-phase 1-2-3 powder with a critical temperature ( T c ) of 92K was produced using reactor temperatures of 900–1000°C. Dry-pressed 1-2-3 pellets densified rapidly at 800–900°C to 89% of theoretical density, which is considerably below the temperatures required for coarser powders produced by other techniques. 1-2-3/CuO particles produced at 800°C consisted of 25–50 nm crystallites of 1-2-3 and CuO, and pellets formed from that powder could be converted to single-phase YBa 2Cu 4O 8 (1-2-4) by heating in atmospheric-pressure oxygen at 750°C for 24 h, followed by 800°C for 24 h. Larger grained 1-2-3/CuO powder (100–250 nm) produced at 900 and 1000°C showed no conversion to 1-2-4 with the same treatment, demonstrating the critical importance of the small grain sizes obtained by aerosol decomposition for rapid conversion of 1-2-3/CuO to 1-2-4.