Partenaires et organisations internationales
(Anglais)
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A, B, CH, CZ, D, E, F, FIN, H, I, IRL, N, PL, S, SI, UK
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Résumé des résultats (Abstract)
(Anglais)
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This study presents a consistent thermodynamic description of the Ag-Bi-Sr-Ca-Cu-O (ABSOCO) system suitable for phase diagram calculations. Every phase of the system is modeled with its Gibbs energy and parameters are optimized based on both phase diagram data and thermodynamic data. This method, which is known as the CALPHAD method, is consistent since it uses simultaneously phase diagram experiments and thermodynamic data. The Bi-Sr-Ca-Cu-O (BSCCO) system contains three high-temperature superconducting phases (HTSC), i.e. the one-layer compound (11905), the two-layer compound (2212) and the three-layer com-pound (2223). HTSC have to be processed in the partially molten state in order to obtain high current densities. Silver is the most adapted substrate for Bi-based HTSC. MgO or CuO-doped MgO are also promising substrates when the substrate has to be an insulating material. The Mg-Cu-O system is optimized and the (Mg,Cu)O sintering is discussed based on thermodynamic considerations. Using the CALPHAD method, we extend the existent database by adding Ag to the BSCCO system. Experimental data are reviewed, phases are modeled and parameters are optimized in the Ag-O, Ag-Bi-O, Ag-Cu-O, Ag-Sr-Cu-O and Ag-Ca-Cu-O systems, as well as in the ABSCCO system around the 2212 compound. Silver is not incorporated in any solid phases of the BSCCO system, especially not in the superconducting 2212 and 2223 compound. For this reason, the modeling and the optimization focus on the liquid phase. The observed decrease of the melting temperature of 2212 by Ag addition is modeled in very good agreement, as well as the eutectic transformation between Ag and 2212. We compare later the calculations with the results obtained on partial melt-processing of 2212 thick films on silver substrates and of 2212 bulk material. The reactions are rather complex since equilibria in re-gard to the oxygen content and in regard to the action redistribution are not always reached. Calcula-tions agree, however, rather well with the partial melt-processing results. Further investigations on the possible existence of a miscibility gap in the oxide liquid are needed, as well as the extension of the system to Pb, which is used to stabilize the 2223 compound.
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