The effect of the configuration of the silver layer on texture growth and microstructure in silver-sheathed superconducting tape

Abstract

Silver-sheathed (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x (2223) tapes with different configurations of silver layer have been prepared to investigate the effect of the silver layer on texture growth and microstructure of the 2223 phase by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDAX). It has been shown that the whole silver layers, both lateral and broad layers, significantly enhance texture growth of the 2223 phase. The new understanding of the mechanistic role of the silver layer in texture growth has been presented, based on the high solubility of oxygen in silver and the greater ability of silver with respect to adsorption of oxygen. The silver layer is thought to supply both a fast out-diffusion path for oxygen formed during the transition from the 2212 phase to the textured 2223 phase and a favourable configuration for texture growth of the 2223 phase.

Formation mechanism of the Pb free phase

“…A similarity between the crystallographic orientation (texture) of the initial Bi(2212) and the final Bi(2223) phase has been reported in some publications [16,61]. This particularity has sometimes been interpreted as a consequence of a transformation mechanism through the intercalation of Ca and Cu-O layers into the Bi(2212) structure [18,22,61]. It has however to be emphasized that Bi(2223) crystals growing from a liquid phase can also inherit the crystallographic orientation of the pre-existing Bi(2212) grains.…”

“…A similarity between the crystallographic orientation (texture) of the initial Bi(2212) and the final Bi(2223) phase has been reported in some publications [16,61]. This particularity has sometimes been interpreted as a consequence of a transformation mechanism through the intercalation of Ca and Cu-O layers into the Bi(2212) structure [18,22,61].…”

“…(ii) The present observations were performed on the external surface of a sample. The growth of the Bi(2223) crystallites can proceed without external mechanical and/or geometrical constraints as would be the case in the inner parts of a pellet or near to the Ag sheath of a tape [61,65].…”