Effects of Pb in the first stages of the Bi(2223) phase formation

Abstract

The reaction of the precursor powders necessary for the formation of t h e final Bi(2223) phase was investigated with and without the presence of an Ag sheath by means of differential thermogravimetry (DTWDTG). The nature of t h e endothermic peaks observed by D T A ~~ well as the influence of Ag on their positions are discussed. By means of x-ray diffraction and energy dispersive x-ray analysis (EDX) on oil-quenched Ag-sheathed tapes it is shown that the Bi(2212) phase originally present in the precursor powders undergoes a structural modification which can be associated with the dissolution of Pb. This transformation occurs at a temperature near 836°C in Agsheathed tapes. This work h a s been essentiallyfocused on t h e role of Pb and its effects on the Bi(2212) phase i n the first stages of transformation.

Dta/TG study of the formation of the (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductor

“…3) is likely to be related to the disappearance of the Ca2PbO 4 and 3221 phases by reaction with other compounds of the matrix. During this stage, Pb was found by EDX to be again incorporated into the Bi,Pb(2212) phase [7]. Considering that one oxygen atom is released by each Pb atom, the maximum expected weight loss (assuming that all the Pb contained in the nominal composition enters into consideration) is equal to 0.60 mg, in good agreement with the experimentally observed 0.62 mg for Am 2.…”

“…It appears that the compositions that are richer in Cu pres- ent the more prominent partial melting peak. This is not surprising since CuO is implied in this reaction [7]. Pellets of those calcined precursor powders have been sintered at 857~ for various lengths of time, resulting in the formation of the Bi,Pb (2223) imaginary component (~") of the ac-magnetic susceptibility of the sintered samples revealed a peak characteristic of the intergranular superconducting transition (inset in Fig.…”

Enhanced critical current density in (Bi,Pb)-2223/Ag tapes prepared using precursors calcined in dynamic vacuum with oxygen partial pressure

“…2 shows the DTA plots of the precursors taken at a heating rate of 10 -C min À 1 in static air. All the precursors except PVA exhibit two distinct endotherms, the first corresponding to the partial melting of a phase rich in Ca 2 PbO 4 and the second the melting of 2212 phase [22,23]. In the case of PVA the endotherm corresponding to the partial melting is absent as it does not contain sufficient amount of Ca 2 PbO 4 phase for liquid phase formation.…”

Effect of MgO Nanorod Doping on Phase Formation and Intergrain Coupling of (Bi, Pb)-2223 Superconductors

“…1. According to previous studies [17,18], the endothermic peak is due to partial melting of the powders, which is of special importance because it is related to the sintering temperature of the samples. It has been well established that the optimum sintering temperature is just below the partial melting temperature.…”