New Aspects on Fluorination of Bi(Pb)-Sr-Ca-Cu-O -Reasons for the Improved Superconducting Properties.-Bi(Pb)-Sr-Ca-Cu-O(F) superconductors are prepared by freeze-drying of solutions of the corresponding metal cations in the presence of F-, followed by calcination at 730 • C and sintering at 750-850 . degree.C. Powders of composition Bi1.85Pb0.35Sr1.91Ca2Cu3OyFx with x ranging from 0 to 0.79 mole are produced by this method. The superconducting properties are found to depend on the sintering conditions. At a sintering temp. of 840 • C, a significant reproducible increase of the superconducting volume fraction with increasing Fcontent is observed, whereas the superconducting properties of samples sintered below 830 • C are not improved by the fluorination. It is suggested that a grain size effect is responsible for the improved superconducting properties of the fluorinated materials sintered at the higher temperature. -(KEMNITZ, E.; SCHEURELL, S.; NAUMOV, S. W.; KASIN, P. E.; PERSHIN, V. I.; KREMER, R. K.; Eur.
The influence of oxidative and nonsxidative chlorination on the chemical and superconducting properties of (Si, Pb),Sr,Ca,Gu,O, is studied on samples with different initial 0 content. Owing to oxidative chlorination of Odeficient phases a significant increase of T. is observed although insulating, hygroscopic halide phases are formed and indications for the incorporation of Ci into the structure are not found. Obviously, reactive 0 is formed during degradation of the 2223 phase on the solid-gas phase boundary. The released 0 partially occupies anion vacancies in the unreacted Odeficient mateiial resulting in improved intragranuiar superconducting behaviour. The reaction pathways of the heterogeneous solid-gas reaction are discussed on t h e basis of the results of chemical analysis.
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