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

Bulk ceramic samples with Bi1.72Pb0.34Sr1.87Ca1.91Cu3.13O9.83−x F 2x (0.00 ≤ x ≤ 0.51) nominal compositions were synthesized by a solid-state route using SrF2 as a fluorine source. Notwithstanding of the stage, at which SrF2 was introduced into the precursor powders (prior to or after calcination), a significant lowering of the reaction temperature was observed.

For a fixed sintering temperature, SrF2 results in an enhanced grain growth. However, the lattice parameters of the Bi2223 phase and its superconducting transition temperature are not significantly affected by the presence of fluorine. The beneficial effect of SrF2 in terms of promoted Bi2223 phase formation appears to be limited to low SrF2 contents.

It is believed that the observed effects are due to the fact that an increasing proportion of Sr is kept apart from the reaction for increasing SrF2 level, rather than to a direct involvement of fluorine.