Influence of surface doping on sintering and microstructure of a superconducting oxide

The influence of surface halogen doping on the sintering and microstructure of Y1Ba2Cu3O7-x (YBCO) has been investigated. It is seen that exposing the starting YBCO powder to Br gas prior to sintering results in secondary recrystallization and formation of long columnar grains. The chemical composition and structure of the overall material is unchanged indicating that it is only the microstructure that is effected by the bromine. Since large domain sizes and preferred orientations are key to electrical and levitation properties of these materials, this effect of increased grain growth may prove to be very useful in controlling the texture of these materials. Even in randomly mixed composites of Ag and YBCO, Br is seen to increase the grain size and porosity of the YBCO regions, indicating that grain growth outpaces pore elimination. It is likely that Br, as a surface additive, enhances liquid phase formation and/or increased diffusion at the interfaces that lead to these effects. The atomistic mechanism of the process and the quantitative optimization of the doping concentration need to be investigated. (C) 1999 Elsevier Science B.V. All rights reserved.