Reversible melting and equilibrium phase formation of (Bi,Pb)2Sr2Ca2Cu3O10+d

The decomposition and the reformation of the (Bi,Pb)2Sr2Ca2Cu3O10+d (?Bi,Pb(2223)?) phase have been investigated in-situ by means of High-Temperature Neutron Diffraction, both in sintered bulk samples and in Ag-sheathed monofilamentary tapes. Several decomposition experiments were performed at various temperatures and under various annealing atmospheres, under flowing gas as well as in sealed tubes, in order to study the appropriate conditions for Bi,Pb(2223) formation from the melt. The Bi,Pb(2223) phase was found to melt incongruently into (Ca,Sr)2CuO3, (Sr,Ca)14Cu24O41 and a Pb,Bi-rich liquid phase. Phase reformation after melting was successfully obtained both in bulk samples and Ag-sheathed tapes. The possibility of crystallising the Bi,Pb(2223) phase from the melt was found to be extremely sensitive to the temperature and strongly dependent on the Pb losses. The study of the mass losses due to Pb evaporation was complemented by thermogravimetric analysis which proved that Pb losses are responsible for moving away from equilibrium and therefore hinder the reformation of the Bi,Pb(2223) phase from the melt. Thanks to the full pattern profile refinement, a quantitative phase analysis was carried out as a function of time and temperature and the role of the secondary phases was investigated. Lattice distortions and/or transitions were found to occur at high temperature in Bi,Pb(2223), Bi,Pb(2212), (Ca,Sr)2CuO3 and (Sr,Ca)14Cu24O41, due to cation diffusion and stoichiometry changes. The results indicate that it is possible to form the Bi,Pb(2223) phase from a liquid close to equilibrium conditions, like Bi(2212) and Bi(2201), and open new unexplored perspectives for high-quality Ag-sheathed Bi,Pb(2223) tape processing.Comment: 45 pages (including references,figures and captions), 13 figures Submitted to Supercond. Sci. Techno

Sections efficaces des réactions (γ, p) produites par des rayons γ de 14.8 et 17.6 MeV sur les éléments Al, Ni, Cu et Ag

The cross-sections of (γ, p) reactions induced on Al, Ni, Cu and Ag by the γ radiation from the 7Li (p, γ) reaction have been measured relatively to the known cross-section σ0 of the 63Cu (γ, n) reaction. Assuming for σ0 the value (82 ± 8) mbarns, the obtained cross-sections are : σ(Al) = (7.2 ± 1,1) mbarns, σ(Ni) = (43 ± 5) mbarns, σ(Cu) = (9.8 ± 1.4) mbarns, σ(Ag) = (6.2 ± 0.9) mbarns. These results have been used to compare the ratios σp/σn of the cross-sections for the (γ, p) and (γ, n) reactions on Ni, Cu and Ag, with the data from the statistical theory.Les sections efficaces des réactions (γ, p) produites sur les éléments Al, Ni, Cu et Ag par le rayonnement γ de la réaction 7 Li (p, γ) ont été mesurées par comparaison avec la section efficace σ0 de la réaction 63Cu (γ, n). En retenant pour σ0 la valeur (82 ± 8) mbarns, les sections efficaces obtenues sont σ(Al) = (7,2 ± 1,1) mbarns, σ(Ni) = (43 ± 5) mbarns, a(Cu) = (9,8 ± 1,4) mbarns, σ(Ag) = (6,2 ± 0,9) mbarns. Ces résultats ont été utilisés pour comparer les rapports σp/σn des sections efficaces des réactions (γ, p) et (γ, n), pour les éléments Ni, Cu et Ag, avec les prévisions de la théorie statistique

Section efficace de la réaction 12c(γ, 3α) à 14,8 et 17,6 MeV

Pas de Résumé disponibl