Influence of heat treatment conditions on the phase composition and superconducting properties of Bi1.6Pb0.4Sr1.98K0.02Ca2Cu3F0.8Oy ceramic

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.…”

“…Lee et al [3] obtained a T c of 116 K in samples produced by reacting a mixture of Bi 2 O 3 , PbO, SrCO 3 , CaCO 3 , CaF 2 and CuO at 838 • C. However, in a recent work by Amira et al [18], a similar preparation technique with CaF 2 yielded T c values limited to less than 110 K. Wei et al [2] used CuF 2 instead of CaF 2 as a fluorine source and could observe superconducting transitions at up to 118 K, but more recent reports on the use of CuF 2 in a solid-state reaction route did not succeed in reproducing this promising result [7,19,20]. According to Gao et al [4], using PbF 2 amongst the starting reagents instead of PbO results in a T c as high as 121 K, but here again, no confirmation was achieved by other groups, neither using solid-state reaction routes [9,15,17], nor sol-gel techniques [8,10]. Watanabe et al [6] on the other hand reported on the observation of a T c = 117.5 K in a single sample prepared by solidstate reaction with BiF 3 as starting reagent.…”

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“…The phase composition of the synthesized materials was studied by x-ray diffraction (XRD) using Cu Kα radiation. The per cent ratio of the superconducting phases (neglecting other non-superconducting phases) was determined by measuring the intensities of the reflections (0010) and (008) of the 2223 and 2212 phases, respectively [14]. The morphology of the surfaces and the composition of the samples were examined by scanning electron microscopy (SEM) on a JEOL JSM-820 equipped with Link Analytical Systems LZ-5 energy dispersive x-ray (EDX) facilities.…”

“…Previously, we synthesized superconducting samples with a nominal composition of Bi 1.6 Pb 0.4 Sr 1.98 K 0.02 Ca 2 Cu 3 F 0.8 O y possessing T c (R = 0) = 112.8 K and studied the stability of this phase in the temperature range between 845 and 890 • C [14].…”