ChemInform Abstract: New Aspects on Fluorination of Bi(Pb)‐Sr‐Ca‐Cu‐O ‐ Reasons for the Improved Superconducting Properties.

Abstract

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.

Influence of SrF2 on the Formation, Microstructure and Critical Temperature of (Bi,Pb)2Sr2Ca2Cu3O10 Polycrystalline Samples

“…This interest originates in an early report by Horiuchi et al [1] showing a clear enhancement of the critical temperature (T c ), when a part of the CaCO 3 powder used for the solid-state reaction synthesis is replaced by CaF 2 . However, whereas improvements were confirmed in some further reports [2][3][4][5][6][7][8][9], in many instances, no increase of T c could be observed [10][11][12][13][14][15][16][17][18][19][20]. The discrepancies might be related to the various synthesis techniques tested for doping the Bi2223 phase with fluorine.…”

Interaction of Bi(Pb)-2223/2212 ceramics with

“…The corresponding χ values reflect the content of Bi-2223 phase. The magnetic response depends to some extent on the grain size also as a result of grain dimensions comparable with the London penetration depth λ so that small grains exhibit lower −χ values [17]. In any case the −χ enhancement corresponds to the Bi-2223 phase formation process expressed both in the Bi-2223 content and in its grain growth.…”

(Cu,C)Ba2Ca3Cu4Ox–(LiF)y: addition of LiF—an effective way to synthesize overdoped superconductor

“…Being in the highly overdoped state, the influence of F might be washed out by the stronger influence of Li. It was also found that F enhances the grain growth in Bi-2212 [36], Bi-2223 [37] and Hg, Re-1223 [38]. It is interesting that Kikuchi et al [39] observed the occurrence of whisker type grains in Tl-1223 when using TlF as source material instead of Tl 2 O 3 .…”