2223 Phase Formation in Bi(Pb)─Sr─Ca─Cu─O: I, The Role of Chemical Composition

Abstract

The formation of superconducting phases in the Bi(Pb)-Sr-Ca-Cu-0 system has been systematically investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPIMA, ICP-AES, fourprobe dc resistance, and ac susceptibility. Starting compositions, firing temperature, and the duratilon of heat treatment, together with the atmosphere, were found1 to be critical in determining the preferred formation of the 2223 phase. This paper reports the effect of the initial chemical composition, emphasizing the importance of compositional control in the synthesis of the single 2223 phase. It has been shown that, with a correct starting composition and predetermined synthesis conditions, single 2223 phase can be obtained without intergrowth by the 2212 and other impurity crystalline phases. The optimum starting composition for the preferred growth of the 2223 phase was identified as being Bi,,7Pbo.3+ySr*CazCu30~ (y = O . l ) , with excess Pb added in order to compensate for its loss at high temperatures. The effect of Pb doping and excess Cu on the phase formation in the Bi oxide based superconducting system is discussed.[

Phase coexistence and critical temperatures of the (Bi, Pb)2Sr2Ca2Cu3Ox phase under partial pressures of oxygen between 10−3 and 0.21 bar with and without additions of silver

“…However, the 2212 phase appears to be present again above the thermal decomposition line of Bi, Pb(2223). 5,6 For a given oxygen pressure there exist three different possibilities for the annealing temperature dependence of the second phase content of the specimens, denoted (a), (b), or (c) in Fig. 4.…”

“…However, as this phase cannot be prepared in a pure state other phases are always present during the measurements. Later studies 4,5 focused on the phase formation and phase formation kinetics of, in particular, the lead-doped version of the phase. Very recently the influence of lead on this decomposition line was reported.…”

Critical aspects on preparation of Bi-2223 glassy precursor by melt-process

“…The melt process is highly dependent on Bi 2 O 3 that lowers the total melt temperature as described by Tampieri et al [72]. Although both Bi 2 O 3 and CuO are no glass forming oxides, such as SiO 2 and B 2 O 3 , it is recognized that they are necessary to form a glassy state in the Bi-Sr-Ca-Cu-O system [5,60]. Komatsu et al [1] proposed the network structure model in Bi-based glasses as follows: BiO 6 octahedra are connected to other BiO 6 octahedra through two-coordinate Cu + ions.…”

“…According to Wong-Ng et al [76], excess amounts of Ca and Cu are needed for the formation of significant quantities of high-T c phase. Chen and co-worker [60,77,78] found that the optimum composition should be stoichiometric in Ca and Cu, but with a slight excess of Pb. However, all these reports have in common that the chemical composition of the glassy material after the quenching step was not analyzed.…”

“…The melt temperature and time should be chosen as low as possible to avoid the evaporation of Bi and Pb but ensuring a complete melt. For example, melt temperatures above 1300°C should lead to that the chemical composition for Bi and Pb after the process would not roughly be the same as the initial composition [1,60].…”