A new model for the formation of high-T c phase in superconductive (Bi, Pb)2Sr2Ca2Cu3O x glass-ceramics

Abstract

The formation mechanism of the high-To phase through the glass-ceramic route and the role of Pb on the formation of this phase have been investigated. It was found that a new compound with the chemical composition Pb2Sr3 xCaxCuOv (x = 1.8) precipitates at around 550°C. This phase is stable up to 800°C, where it begins to decompose, and at 850°C it completely disappears. It was found that some part of the released Pb diffuses into the 2212 phase leading to the formation of Pb-containing 2212 phase, (Bi,Pb)2Sr2CaCu2Ox. On the other hand, an endothermic peak, probably arising from the melting of (Bi,Pb)2Sr2CaCu2Ox phase or melting at grain boundaries containing Pb 2+, was observed at 856°C only in Pb-containing samples that were heat treated. The liquid phase attributed to the endothermic peak may enhance the formation of high-Tc phase (2223 phase). The growth kinetics for the high-To phase were analysed using the Johnson-MehI-Avrami equation; the results indicate that the growth of the high-To phase is controlled by a diffusion process and the activation energy for its formation in the initial stage (shorter than 96 h) is 576_+45 kJ tool -1

The Effect of Zn Substitution of Ca in BiPbSrCaCuO Superconductors Sintered at 830 °C

“…The phase of Bi 2 Sr 2 CuO y (2201) with minor peaks of Ca 2 PbO 4 and 2212 was formed as the major phase at 700°C. On the other hand, the formation of major low-T c 2212 and minor high-T c 2223 phases was observed in ceramics annealed at 800°C [21]. Ca 2 PbO 4 phase plays a crucial role in the formation of high-T c superconducting films and bulk specimens.…”

Bi(Pb)-2223 phase formation in Ag-sheathed tapes: the role of oxygen partial pressure during sintering

“…Lead oxide compounds enhance the Bi(Pb)-2223 phase formation as described in the literature [12]. According to Khaled et al the '3321' phase triggers the transformation of…”

“…The fractional conversion from the Bi(Pb)-2212 into Bi(Pb)-2223 was calculated from the x-ray intensity ratios of the (0010) peak of the Bi(Pb)-2223 and the (008) peak of Bi(Pb)-2212 [7]. The presence of the lead oxide compounds was determined from the peaks of Sr 2 PbO 4 (17.4 • ), Ca 2 PbO 4 (17.8 and 18.2 • ) and Pb 3 Bi 0.5 Sr 2.5 Ca 2 Cu 1 O x -the so-called '3321' phase (18 • ) [12]. SEM and EDX elemental mapping techniques were applied in a JEOL JSM840 microscope equipped with a LINK EDX detector.…”

High temperature XRD on silver sheathed Bi(Pb)-2223 tapes in different oxygen partial pressures

“…In order to investigate the influence of the sintering temperature on the formation of lead oxide compounds, tape A was heated and diffraction patterns were measured in steps of 10 • C. The plumbate compounds-in this case the 3321 phase [8]-appear for 8 kPa O 2 at a temperature of about 560 • C (figure 2) and vanish at about 810 • C. Subsequently, the sample was fast cooled from 820 • C to room temperature within half a minute (1600 K min −1 ). After this quenching process the 3321 phase could no longer be detected.…”

“…Bi(Pb)-2223 powders with an overall composition of (A) Bi 1.72 Pb 0.32 Sr 1.81 Ca 1.9 Cu 3.0 O x (Endo stoichiometry with a phase composition of Bi(Pb) 2 Sr 2 CaCu 2 O x (Bi(Pb)-2212), Ca 2 CuO 3 (calcium cuprate) and CuO (copper oxide)) and (B) Bi 1.8 Pb 0.4 Sr 2.0 Ca 2.1 Cu 3.0 O x (Sato stoichiometry with a phase composition of Bi-2212 [7], Pb 3 Bi 0.5 Sr 2.5 Ca 1.5 Cu 0.5 O x (3321) [8], Ca 2 PbO 4 (calcium plumbate) [9], Ca 2 CuO 3 (calcium cuprate) [10] and CuO (copper oxide) [11]) were placed in an Ag tube and cold worked to a 55-filament tape by established techniques [1,12]. The corresponding diffraction patterns are shown in figure 1.…”