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Interface and grain boundary structures in YBa2Cu3O7-x and YBa2Cu4O8 materials |
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| Authors: | Z L Wang R Kontra D M Kroeger A Goyal R K Williams |
| Institution: | (1) Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, 37831-6376 Oak Ridge, TN;(2) Present address: Metallurgy Division, National Institute of Standards and Technology, Bldg. 223, 20899 Gaithersburg, MD;(3) Present address: IBM, D324, Bidg, 967-2, 05402 Essex Jct., VT |
| Abstract: | Y2BaCuO5YBa2Cu3O7-x (Y211/Y123) interfaces in melt-processed YBa2Cu3O7-x were studied by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Yttrium enrichment and barium depletion were observed locally at the Y211/Y123 interfaces where Y123 (001) facets were present. This effect may be interpreted as the result of lattice substitution of Ba by Y near these interfaces. Cation nonstoichiometry was found near Y211/Y123 interfaces where liquid phases (Cu-Ba-O) were present. This chemical disorder introduces numerous point defects in the Y123, and these defects may act as additional pinning sites alongwith stacking faults. A comparison of grain boundary (GB) chemical composition in polycrystalline YBa2Cu3O7-x and YBa2Cu4O8(Y124), studied using nanoprobe parallel-detection electron energy-loss spectroscopy (EELS), is presented. The studies of Y124 show that stoichiometric grain boundaries can also form weak links between superconducting grains. It is suggested that weak-link behavior is determined largely by misorientation at grain boundaries. |
| Keywords: | Y2BaCuO5-YBa2Cu3O7-x interface point defeets flux pinning cation nonstoichiometry grain boundary chemistry oxygen deficiency hole density grain boundary misorientation high-resolution transmission electron microscopy (HRTEM) energy dispersive X-ray spectroscopy (EDS) electron energy-loss spectroscopy (EELS) |
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