Role of lead substitution in the production of 110-K superconducting single-phase Bi-Sr-Ca-Cu-O ceramics

Abstract

We have systematically investigated the influence of the three parameters (temperature of sintering, lead content, and duration of the sintering) on the growth of the (2:2:2:3) phase in ceramics of nominal composition Bi2−xPbxSr2Ca2Cu3O10−x/2, and have determined the compositions and thermal conditions leading to ceramics with Tc≊110 K and containing more than 95% of this phase. We show that this result can be obtained by usual calcination near 880°C in air, without recurring to the introduction of excess in the constituants, providing that intermediate grinding are effected, in order to reactivate the formation of the (2:2:2:3) phase which otherwise saturates for long durations of sintering. The suitable nominal compositions (0.3≤x≤0.4) correspond to those that yield inside the grains a lead content in the vicinity of the limit of solubility for lead. From the results of the preceding investigations and of experiments effected on lead-substituted single crystals of the (2:2:1:2) phase, we have clarified the role played by lead, at the microscopic level, in the enhancement of the formation of the (2:2:2:3) phase. The inferred role is the establishment of strong bonding between the slabs which are the buildings blocks of the structure of the superconducting phases, these slabs being almost independent in the lead-free compounds. The origin of the stronger bonding is discussed.

Mode of lead addition and its effects on phase formation and microstructure development in composite conductors

“…The sharpest transition temperatures (T c ) and highest J c values were observed when 75-100% of the lead was incorporated in the Bi-2212 phase, rather than in the Pb-Ca-Cu-O component of the starting powder. This result is in contradiction with previous reports of the beneficial role of Ca 2 PbO 4 on the growth kinetics and J c properties of one-powder type Ag/Bi-2223 composites [11][12][13][14]22], suggesting that the one-powder and two-powder reaction mechanisms/kinetics for Ag/Bi-2223 composites are not exactly the same.…”

“…Lead addition to the Bi-Sr-Ca-Cu-O system was found to enhance diffusion, accelerate reaction kinetics and give stability to the Bi-2223 phase [8][9][10] and is associated with decomposition and partial melting of lead-rich phases (e.g. Ca 2 PbO 4 ) during the formation of the Bi-2223 phase [5,[11][12][13][14]. The optimal stoichiometric amount for lead addition to Bi-2223 is reported to be 0.35-0.4 moles [10,15].…”

Transport, microstructure and mechanical properties of Au diffusion-doped Bi-2223 superconductors

“…To improve the superconducting properties, partial substitution has been investigated extensively [1][2][3][4][5][6][7]. Phases of Bi-based system are highly reactive and not very stable.…”

The effect of Au diffusion on some physical properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

“…To improve the superconducting properties, partial substitution has been investigated extensively [1][2][3][4][5][6][7][8][9][10][11]. After the discovery of Bi(Pb)-Sr-Ca-Cu-O system, researchers began to investigate answers of questions such as what happens * Corresponding author.…”