The oxygen content of the high-temperature superconducting compound Bi2+xSr3−yCayCu2O8+d as a function of the cation concentration
01 Aug 1994-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 229, Iss: 1, pp 12-16
TL;DR: In this article, the oxygen content of Bi2+xSr3−yCayCu2O8+y (2212 phase) has been determined as a function of its cation concentration.
Abstract: The oxygen content of Bi2+xSr3−yCayCu2O8+y (2212 phase) has been determined as a function of its cation concentration. With increasing Ca and Bi content the oxygen content increases and Tc decreases. The oxygen content of Ca rich 2212 phase increases with decreasing annealing temperatures. The study shows that the Tc of the 2212 phase primarily is controlled by its cation concentration.
Citations
More filters
TL;DR: In this paper, the phase diagram studies with emphasis on the high temperature superconducting phases (2212 phase) and (2223 phase) are reviewed in detail at various temperatures and oxygen partial pressures.
Abstract: Phase diagram studies with emphasis on the high temperature superconducting phases (2212 phase) and (2223 phase) are reviewed in this article. The phase relations of the and the homogeneity regions of the 2212 and 2223 phases have been studied in detail at various temperatures and oxygen partial pressures. However, the Pb-doped system has been investigated less comprehensively. The studies of this system are mostly focused on the 2212 and 2223 phase and the experimental work regarding the 2223 phase is often concentrated on the processing of 2223 samples with high critical current density and not on the preparation of single phase 2223 ceramics. The investigations of the Ag-containing system have just started. Nevertheless, first results show that Ag significantly influences the phase relations and the temperature dependence of the cation solubilities of the 2212 and 2223 solid solutions. These results indicate that the obtained phase diagrams of the system cannot be applied without caution when Ag is present. Therefore, as Ag is widely used as a sheath material for the processing of 2212 and 2223 wires and tapes, the investigation of the entire Ag-containing system is inevitable.
107 citations
TL;DR: In this article, the results of studies of crystal chemistry and phase equilibria are presented to give materials scientists a comprehensive insight into the phase equilibrium and crystal chemistry of these challenging materials.
Abstract: Ten years after the discovery of high-Tc superconductivity in the system Bi-Sr-Ca-Cu-O, the superconducting compounds have been identified, and their structures, crystal chemistry, phase equilibria, and properties have been extensively investigated. In this review, the results of studies of crystal chemistry and phase equilibria are presented to give materials scientists a comprehensive insight into the phase equilibria and crystal chemistry of these challenging materials.
84 citations
TL;DR: In this article, an alternative approach using the direct conversion of metallic precursors (MPs) to Bi2Sr2CaCu2Ox(Bi2212)/Ag multifilamentary wires is studied.
Abstract: Bi2Sr2CaCu2Ox(Bi2212)/Ag multifilamentary wires are manufactured via the powder-in-tube process using oxide powders. After deformation, the wires undergo a partial-melt process, resulting in a complex, heterogeneous microstructure containing multiple secondary phases and porosity, limiting the wires? electrical and mechanical performance. Here, an alternative approach using the direct conversion of metallic precursors (MPs) to Bi2212 is studied. The formation of metallic precursor powders via a mechanical alloy is discussed. The MP powder is then converted to superconducting Bi2212 through a simple two-step heat treatment. By introducing oxygen at a temperature at which Bi2212 is in a stable phase, and holding at an elevated temperature for a sufficient time, the metallic precursors are oxidized and transformed into Bi2212. Several factors that impact the formation and growth of Bi2212 grains are discussed. Peak temperature, holding time and heating rate are shown to affect the MP ?Bi2212 conversion, the Bi2201 content and the Bi2212 morphology and density. It is found that Bi2Sr2CuOy (Bi2201) can be the only phase impurity after heat treatment, which is quite different from what is observed in partial-melt processed wires derived from oxide precursors. Lastly, the microstructure at the sample/silver interface suggests larger size and preferred orientation of Bi2212 grains with the aid of a silver surface. Implications for MP Bi2212 wires are discussed.
71 citations
TL;DR: The negative-U interpretation of high-temperature superconducting (HTSC) behavior in the mixed-valent, square-planar cuprate metals is pursued further in this paper.
Abstract: The two-subsystem, negative-U interpretation of high-temperature superconducting (HTSC) behaviour in the mixed-valent, square-planar cuprate metals is pursued further. The question of the symmetry of the order parameter is central to understanding the HTSC phenomenon. Many have by now examined the potentialities of a mixed order parameter to cope with the wealth of data of all types available from these materials. It is emphasized here that it is actually a mistake for the present mixed-valent, highly tight-binding systems to seek a single, spatially homogeneous, compound order parameter. The systems are demonstrably micro-inhomogeneous due to charge segregation as in many substituted systems very close to Mott localization. In these circumstances there is a fascinating interplay between magnetism, charge and structural aspects to the problem at the unit cell level. Questions of local moment seeding, of local trapping of carriers structurally and magnetically, of on-site Jahn - Teller and bonding distortions, on the one hand, are highly intertwined, on the other, with somewhat more delocalized aspects to the problem, like SDWs, CDWs, the resonant valence band state, etc. All these matters have to be treated simultaneously, in a way appropriate to the precise level of carrier doping secured. Control over the outcome is dependent, moreover, from system to system upon the detailed degree of covalency introduced into the problem by the particular counter-ions employed. The present review makes an attempt to hold together all the published information on a coherent basis. That basis is seen as being provided by a negative-U sequencing of state energies in the mixed-valent cuprates, once it is accepted that the systems are not homogeneous at the micro-level. Results on the LSCO system, for example, find interpretation in terms of moderately well organized discommensurations in charge and spin distribution. The fact that this approach has been followed from the beginnings of high-temperature superconduction, now nearly ten years ago, without any sustained discouragement from the accumulating data, indicates that it provides a means of interpretation worth more direct attention than it has received to date. In particular it provides very naturally a means to understand what it is that confines high-temperature superconduction to its narrow range - the square-planar, layered, mixed-valent cuprates. There is in essence only one high-temperature superconductor and this paper attempts again to say why.
30 citations
TL;DR: In this article, the effect of oxygen pressure on growth conditions is studied, in contrast with air growth, the instability of molten zone occurs under high oxygen pressure applied during the growth, in consequence of the precipitation of impurity phases on crystallization front.
Abstract: Overdoped Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi-2212) single crystals have been prepared by travelling solvent floating zone technique under high oxygen pressure up to 10 bar. The effect of oxygen pressure on growth conditions is studied. In contrast with air growth the instability of molten zone occurs under high oxygen pressure applied during the growth, in consequence of the precipitation of impurity phases on crystallization front. The feed rods pre-melted over 4 bar oxygen pressure were found to contain minor impurity phases, and this could also affect the stability of molten zone. With increasing oxygen pressure from 2 to 10 bar the ratio of Bi/Sr for the overdoped Bi-2212 crystals increases in subsequent to the decrease of c -axis from 30.890(6) to 30.653(8) A, while the T c reduces from 95 to 81 K. Besides the oxygen growth pressure T c and ΔT c of the overdoped crystals are influenced by growth rate and feed rod pre-melting conditions.
19 citations
References
More filters
TL;DR: In this article, the cation solubility limits of the n= 2 and n= 3 superconducting phases in the Bi2(SrxCa1 −x)n+1CunOy system were established along tie lines with compatible phases via electron probe microanalysis on bi- or poly-) phasic samples prepared at 860°C.
Abstract: The cation solubility limits of the n= 2 and n= 3 superconducting phases in the Bi2(SrxCa1 −x)n+1CunOy system were established along tie lines with compatible phases via electron probe microanalysis on bi- (or poly-) phasic samples prepared at 860°C. Pb additions (15 mol% of the Bi content) were used to facilitate formation of the n= 3 phase. In each case football-shaped volumes in composition space were established as the solubility limits which bordered on the nominal compositions 2212 or 2223 (Bi:Sr:Ca:Cu) with the long axis parallel to the Sr-Ca side of the quaternary (i.e., Sr-to-Ca intersolubility) but also extending toward Bi and Cu. This means that, for the most part, the superconducting phases are alkaline-earth deficient relative to the ideal 2212 and 2223 compositions. The Pb content in the 2223 phase is typically 10% of the Bi content. Tc variations could be correlated with variations in Sr or (Sr + Bi) content and the length of the c-axis parameter.
91 citations
TL;DR: In this article, the authors derived multiphase equilibria for the 2-layer superconductor Bi 2 (Sr 1− x Ca x ) 3 Cu 2 O 8, which is a trigonal bipyramid with a length of 13.7 mol% parallel to the SrOCaO edge, and an extension of 9 mol% perpendicular to it.
Abstract: The extension of the single-phase field of the two-layer superconductor Bi 2 Sr 2 CaCu 2 O 8 is clarified for 830°C in air. The single-phase field of “2212” is a trigonal bipyramid with a length of 13.7 mol% parallel to the SrOCaO edge, and an extension of 9 mol% perpendicular to it. The tolerance of the lattice concerning CuO variation is smaller than ± 1.2 mol%. The CaO-rich solid solution is deficient in CuO compared to the ideal 2212 solid solution, Bi 2 (Sr 1− x Ca x ) 3 Cu 2 O 8 , whereas the SrO-rich side has excess CuO. Multiphase equilibria around “2212” as well as the single phase field were derived by combining the XRD and EDX results of 91 samples of different compositions with the previously published results. The intersections of the multiphase equilibria with three different planar sections of the compositional tetrahedron are shown.
71 citations
TL;DR: In this paper, a melt casting process tailor made for BSCCO, especially for the 2212 phase, is described, and the properties of the material obtained by MCP have been significantly improved by admixing strontium sulphate.
Abstract: A melt casting process (MCP) that is tailor made for BSCCO, especially for the 2212 phase, is described. It is reported that melt casting offers an easy access to a variety of different shapes and sizes. The properties of the material obtained by MCP have been significantly improved by admixing strontium sulphate. J/sub c/ values superior to those of sintered ceramics of YBCO or BSCCO have been obtained: J/sub c/ values at 55000 A/cm/sup 2/ (4 K) and 2200 A/cm/sup 2/ (77 K) were achieved without external fields; large bulk parts exhibited more than 2000 A (77 K) in their self-field. The peculiarities of MCP allow the integration of noble metal current contacts which exhibit total resistances >
64 citations
62 citations
TL;DR: The phase relationships and solid-solution region of the Bi 2 Sr 2 Ca 1 Cu 2 O y (2212) superconductor were investigated for compositions around the ideal 2212 stoichiometry at 865°C in one bar of oxygen as mentioned in this paper.
Abstract: The phase relationships and solid-solution region of the Bi 2 Sr 2 Ca 1 Cu 2 O y (2212) superconductor were investigated for compositions around the ideal 2212 stoichiometry at 865°C in one bar of oxygen. Changes in the starting composition were accommodated by changes in the types and composition of the secondary phases present, the number of intergrowths within the 2212 phase, and the solid solution composition of the 2212 phase. Compositional analysis of the superconducting phase was carried out in the transmission electron microscope (TEM) in order to separate the effects of solid-solution changes and the presence of intergrowths upon measured compositions. The actual solid-solution region determined from TEM measurements showed most of the solid solution substitution to occur between Sr and Ca. The highest superconducting transition temperatures ( T c ) were found in annealed samples for which the measured Sr+Ca content of the 2212 phase was closest to the ideal stoichiometric ratio of 3 (42.86 at.%). No correlation was found between the transition temperature and lattice parameters of the superconducting phase.
61 citations