NanoSIMS analysis of Ca doping at a grain boundary in a superconducting YBCO Ca-123/123 bicrystal

Abstract

Calcium doping is well known to increase the grain boundary critical current, Jcgb, in polycrystalline Y1Ba 2Cu3O7-δ, (YBCO). High resolution Secondary Ion Mass Spectroscopy (nanoSIMS) analysis has been used to map the distribution of Ca+ ions in three dimensions in an YBCO grain boundary grown on a 24° SrTiO3 bicrystal. High resolution SIMS imaging has produced Ca, Sr, and Ti elemental maps at 20 nm intervals from the YBCO surface. From the variation of Ca concentration with depth a Ca grain boundary diffusion coefficient can be estimated. Moreover, localised hot spots of Ca at the YBCO grain boundary have been observed, perhaps at regions with a high dislocation density. There is also some diffusion of Sr and Ti ions from the substrate along the boundary. This is an important observation because it has been proposed that these ions are electrically active. © 2006 IOP Publishing Ltd.