Order-disorder and superconductivity in Ca-doped LaBa2Cu3O7−δ
| Autor: | Huicheng Gu, K. K. Fung, Chongde Wei, Jinlong Zhang, Daole Yin |
|---|---|
| Rok vydání: | 1993 |
| Předmět: |
Superconductivity
chemistry.chemical_classification Copper oxide Materials science High-temperature superconductivity Energy Engineering and Power Technology Condensed Matter Physics Electronic Optical and Magnetic Materials law.invention Tetragonal crystal system Crystallography chemistry.chemical_compound Electron diffraction chemistry law X-ray crystallography Orthorhombic crystal system Electrical and Electronic Engineering Inorganic compound |
| Zdroj: | Physica C: Superconductivity. 208:391-402 |
| ISSN: | 0921-4534 |
| DOI: | 10.1016/0921-4534(93)90213-a |
| Popis: | An analytical electron microscopy study has been undertaken on six superconductors with nominal compositions LaBa 2− x Ca x Cu 3 O 7−δ ( x =0, 0.25, 0.5, 0.75, 1.0 and 1.5). Energy dispersive X-ray spectroscopy (EDXS) analysis shows that the Ca-dopant saturates at doping level x =0.5 for superconducting phases (1-2-3 phases) in these materials, and that further Ca-doping changes only the actual ratio of La/Ba cations and increases the amount of secondary phase Ca 2 CuO 3 . An 80 K T c plateau is found corresponding to this saturation. Convergent-beam electron diffraction (CBED) and transmission electron microscopy (TEM) results show not only that these high- T c 1-2-3 phases are tetragonal with P4/mmm symmetry, but also, based on the observation of several superstructures, that there exists an order-disorder transition in these Ca-doped 1-2-3 phases induced by the variations of La/Ba cation ratios over certain sites in the 1-2-3 unit cell. The high- T c superconductivity in these tetragonal 1-2-3 phases suggests that the Ca cations introduce holes into the bridging site between two conductive Cu-O 2 sheets. This alternative “bridging” hole picture is more general in the high- T c copper oxide family than the “transferring” picture associated with the orthorhombic 1-2-3 phases. |
| Databáze: | OpenAIRE |
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