| Autor: |
T. Graf, Jean-Yves Genoud, Christine Opagiste, Gilles Triscone, Jean Muller, Alain Junod, M. François |
| Rok vydání: |
1993 |
| Předmět: |
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| Zdroj: |
Journal of Alloys and Compounds, Vol. 196, No 1-2 (1993) pp. 235-239 |
| ISSN: |
0925-8388 |
| Popis: |
We have attempted to substitute calcium on the yttrium and barium sites in the “247” superconducting phase, i.e. (Y1 - x Cax)2Ba4 Cu7O15 + δ and Y2(Ba1 - xCax)4Cu7O15 + δ. X-Ray diffraction and microprobe analyses indicate that calcium enters the structure but preferentially occupies the barium site. The solubility of calcium in the “247” phase is clearly lower than 10% (x < 0.1). The samples are not single phase even for small substitutions (x = 0.05). Higher values of x result in a higher amount of impurity phases. The (Y1 - xCax)2Ba4Cu7O15 + δ samples contain BaCuO2 as the major impurity, whereas in Y2 (Ba1 - xCax)4Cu7O15 + δ a new phase is found. This new phase was identified by microprobe analysis to have the composition YCaCu2O4.5 ± δ. No increase is observed in the critical temperature Tc as a function of calcium substitution. This is in contrast with the calcium-substituted “124” superconductor (Y1 - xCax)Ba2Cu4O8 where Tc increases from 80 K (x = 0) to about 90 K (x = 0.1). |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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