TEM imaging of clustered Au substitutional impurities in YBa 2Cu 3O 6.9

Abstract

Evidence for clustering of Au impurity atoms into randomly distributed 1–2 nm rods is presented for YBa 2Cu 3O 7−δ ( δ < 0.1) grown by the self-flux technique in Au crucibles. Electron-diffraction patterns show very weak diffuse streaks along «100å and «010å, and these streaks persist over several degrees of tilt indicating rod-like defects. Multislice image simulations, including the effect of amorphous carbon, for a variety of defect types are compared to high-resolution images. The model that best fits the experimental data is defects made up of 3–4 unit cell long AuO vacancy rods along «010å and AuO interstitial rods along «100å. In light of flux-pinning data comparing YBCO crystals with and without Au doping, these defects should be considered as flux-pinning sites in as-grown Au doped crystals.