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Growth and Superconducting Properties of Pb-Free and Pb-Doped Bi-2223 Crystals
Abstract
High quality single crystals of both Pb-free and Pb-doped Bi-2223 (with sizes up to 3×2×0.1mm<sup>3</sup>) were grown by means of a newly developed "Vapor-Assisted Travelling Solvent Floating Zone" technique in an image furnace. This technique allowed us to grow large Pb-doped Bi-2223 crystals for the first time. Post-annealing in high pressure oxygen (up to 10 MPa) enhanced T<sub>c</sub> (up to 111 K) and sharpened the superconducting transition. The crystal structures of both Bi-2223 and Bi,Pb-2223 were refined and are reported in this paper. The unit cell of the Pb-free average structure is pseudo-tetragonal with a=5.4210(7), b=5.4133(6) and c=37.009(7) Å. An incommensurate structural modulation along the direction of one of the short cell vectors has been defined (q∼0.21 a<sup>*</sup>); however, the structure can be conveniently described in a supercell with a 5-fold volume (a=27.105(4) Å). One additional O atom per translation unit of the modulation wavelength was found to be inserted into the BiO layers. Approximately 8% of the Ca sites are occupied by Bi atoms, and the refined composition is found to be Bi:Sr:Ca:Cu:O=2.16:2:1.84:3:10.16. Similar features are found in the Pb-doped phase. The magnetization of Pb-free Bi-2223 crystals has been studied. The vortex phase diagram has been traced and the anisotropy of Bi-2223 is found to be γ=53 from measurements of the lower critical field, which is much smaller than that of Bi-2212 (γ=165). Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, both of which are signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
... Å] in agreement with previously reported results (see the supplemental material [52], Table 3, and Refs. [70][71][72] therein). Pressure dependencies of the structural parameters of Bi-2223 are presented in Fig. 5. Like Bi-2201 and Bi-2212, no change in the compression of the a axis was apparent, and a slight kink in c was observed at 30 GPa, which is more obvious in the pressure dependence of the c/a ratio [ Fig. 5(b)]. ...
Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-Tc cuprate superconductors with the nominal composition Bi2Sr2Can−1CunO2n+4+δ (n=1,2,3) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of Bi2Sr2Can−1CunO2n+4+δ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of Tc with pressure, including the increase in Tc at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials.
We study a series of spectra measured in the superconducting state of
optimally doped
Bi2Sr2Ca2Cu3O10+δ
(Bi-2223) by scanning tunneling spectroscopy. Each spectrum, as well as
the average of spectra presenting the same gap, is fitted using a
strong-coupling model taking into account the band structure, the BCS
gap, and the interaction of electrons with the spin resonance. After
describing our measurements and the main characteristics of the
strong-coupling model, we report the whole set of parameters determined
from the fits, and we discuss trends as a function of the gap magnitude.
We also simulate angle-resolved photoemission spectra, and compare with
recent experimental results.
A recent polarized x-ray absorption experiment on the high temperature cuprate superconductor Bi2Sr2CaCu2O8 indicates the presence of broken parity symmetry below the temperature, T*, where a pseudogap appears in photoemission. We critically analyze the x-ray data, and conclude that a parity-breaking signal of the kind suggested is unlikely based on the crystal structures reported in the literature. Possible other origins of the observed dichroism signal are discussed. We propose x-ray scattering experiments that can be done in order to determine whether such alternative interpretations are valid or not. Comment: final version to be published in Phys Rev B: some calculational details added, clarification of XNLD contamination and biaxiality, more discussion on possible space groups and previous optics results
Both liquidus and subsolidus phase equilibrium data are of central importance for applications of high temperature superconductors in the (Bi, Pb)-Sr-Ca-Cu-O system, including material synthesis, melt processing and single crystal growth. The subsolidus equilibria of the 110 K high-{Tc} Pb-doped 2223 ([Bi, Pb], Sr, Ca, Cu) phase and the location of the primary phase field (crystallization field) have been determined in this study. For the quantitative determination of liquidus data, a wicking technique was developed to capture the melt for quantitative microchemical analysis. A total of 29 five-phase volumes that include the 2223 phase as a component was obtained. The initial melt compositions of these volumes range from a mole fraction of 7.3% to 28.0% for Bi, 11.3% to 27.8% for Sr, 1.2% to 19.4% for Pb, 9.8% to 30.8% for Ca, and 17.1% to 47.0% for Cu. Based on these data, the crystallization field for the 2223 phase was constructed using the convex hull technique. A section of this volume was obtained by holding two components of the composition at the median value, allowing projection on the other three axes to show the extent of the field.
Large and high-quality single crystals of both Pb-free and Pb-doped high-temperature superconducting compounds (Bi1−xPbx)2Sr2Ca2Cu3O10−y (x = 0 and 0.3) were grown by means of a newly developed 'vapour-assisted travelling solvent floating zone' technique (VA-TSFZ). This modified zone-melting technique was performed in an image furnace and allowed for the first time the growth of large Pb-doped crystals, by compensating for the Pb losses that occur at high temperature. Crystals up to 3 × 2 × 0.1 mm3 were successfully grown. Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 °C) was applied to enhance Tc and improve the homogeneity of the crystals. Structural characterization was performed by single-crystal x-ray diffraction (XRD). Structure refinement confirmed a commensurate modulated superlattice in the Pb-free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 21.829(4) Å, b = 5.4222(9) Å and c = 37.19(1) Å. Superconducting studies were carried out by ac and dc magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔTc ≤ 1 K). In optimally doped Pb-free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2 × 105 A cm−2 were measured at T = 30 K and μ0H = 0 T. A weak second peak in the magnetization loops was observed in the temperature range 40–50 K, above which the critical current density was found to rapidly decrease as a function of T and H. A comparison between the pinning properties in Pb-free and Pb-doped crystals is reported and discussed.
Sizable Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystals were grown by the travelling solvent floating zone technique and subsequently annealed in O2 and/or Ar flow for 120–500 h in a temperature range of 430–850 °C. The effect of annealing on the phase evolution as well as the structural and superconducting properties was studied using x-ray diffraction (XRD) and magnetization measurements as well as ellipsometric measurements of the far-infrared c-axis conductivity. The results show that some of the as-grown Bi-2223 crystals are nearly phase pure, while others contain a certain amount of Bi2Sr2CaCu2O8+δ (Bi-2212), Ca2CuO3 and CuO phases co-existing with the Bi-2223 phase. Annealing these multi-phase crystals in O2 flow at high temperature can lead to a phase transformation from Bi-2212 to Bi-2223, which can be understood by a layer-intercalation mechanism. For the samples consisting of Bi-2212 phase, nearly phase-pure Bi-2223 crystals can be obtained by high-temperature, long-time annealing. Annealing phase-pure crystals in various atmospheres, temperatures and pressures (ranging from 1 to 550 bar) causes an alteration in oxygen content, resulting in a systematic change in the c-axis lattice parameters and superconducting transition temperature Tc. Interestingly, Tc is found to increase with decreasing c-axis lattice parameters reaching K, but change very little with the further decrease of c-axis lattice parameters, exhibiting a broad plateau on the plot of Tc versus c-axis lattice constant. The magnetization and ellipsometric measurements on high-oxygen-pressure annealed Bi-2223 crystals show much stronger Josephson coupling between the CuO2 layers, indicating a progressively higher hole doping upon increasing annealing oxygen pressure, although Tc remains essentially unchanged. The anomalous saturation of Tc on the overdoped side is quite unique compared with the mono- or bi-layered Bi-based cuprates. It is possibly related to the significant difference in the hole doping between the crystallographically inequivalent inner and outer CuO2 planes in the multi-layered cuprate system.
Single crystals of Bi2Sr2Ca2Cu3O10 (Bi-2223) have been grown using the travelling solvent floating zone technique in an image furnace. Annealing the crystals under high pressures of O2 increased their critical temperature to 109 K, and resulted in sharp superconducting transitions of ΔTc = 1 K. The superconducting anisotropy of Bi-2223 was found to be , from measurements of the lower critical field with the magnetic field applied parallel and perpendicular to the c-axis. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi2Sr2CaCu2O8 (Bi-2212), and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
The doping dependence of the themopower, in-plane resistivity rho_ab(T), out-of-plane resistivity rho_c(T), and susceptibility has been systematically measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that the transition temperature Tc and pseudogap formation temperature T_rho_c*, below which rho_c shows a typical upturn, do not change from their optimum values in the "overdoped" region, even though doping actually proceeds. This suggests that, in overdoped region, the bulk $T_c$ is determined by the always underdoped inner plane, which have a large superconducting gap, while the carriers are mostly doped in the outer planes, which have a large phase stiffness. Comment: 5 pages, 4 figures. to be published in PRB
Bi2223 single crystals were grown by the floating zone method with an extremely slow growth rate of 0.05 mm/h. The largest size of the plate-like single crystal was approximately 3 × 2 × 0.1 mm3. The X-ray diffraction analysis and DC susceptibility measurements revealed that the grown crystals were almost single phase of Bi2223 with a very small percentage of Bi2212 intergrowth. Then carrier doping was systematically controlled in a wide range from underdoping to overdoping by post annealing under various conditions. Tc of the crystals was found to vary from 98 K (underdoped) to 108 K (overdoped) with Tc = 110 K for optimally-doped. In the optimally-doped phase the electromagnetic anisotropy factor, γ2 of Bi2223 was smaller than that of Bi2212. Abrupt resistivity drop was observed under fields below the second peak field of the magnetization hysteresis loops, suggesting a first order phase transition of the flux line lattice. Magnetic phase diagram of Bi2223 single crystals for H//c was found to be similar to that of Bi2212.
The traveling solvent floating-zone (TSFZ) method has the potential advantage over the usual flux method that crystal growth can be performed at one point on the temperature–composition phase diagram, and provides an opportunity to grow large single crystals even if their crystallization field is very narrow. Here, we report the first successful preparation of the triple-layered system Bi2Sr2Ca2Cu3O10+δ (Bi-2223) single crystals by improving the TSFZ method condition by applying slow growth velocity and higher temperature gradient. The obtained crystals are as large as 4×2×0.1 mm3. X-ray diffraction pattern shows only sharp Bi-2223 peaks, confirming its good crystallinity. DC susceptibility of the as-grown samples exhibits a sharp superconducting transition with . After annealing the sample under O2 flow at 600°C, Tc increased to the maximum value (=110 K). High-resolution transmission electron microscope images were taken to investigate the phase purity. It confirms that the crystals cleaved from the last part of grown boule are almost single-phase Bi-2223.
The penetration field Hp of Bi2Sr2CaCu2O8+delta crystals is determined from magnetization curves for different field sweep rates dH/dt and temperatures. The obtained results are consistent with theoretical reports in the literature about vortex creep over surface and geometrical barriers. The frequently observed low-temperature upturn of Hp is shown to be related to metastable configurations due to barriers for vortex entry. Data of the true lower critical field Hc1 are presented. The low-temperature dependence of Hc1 is consistent with a superconducting state with nodes in the gap function.
Single crystals of (Bi, Pb)2Sr2Ca2Cu3Ox (Tc=110 K), prepared by fused-salt reaction technique [S.-Y. Chu, M.E. McHenry, J. Mater. Res. 13 (1998) 589; S.-Y. Chu, M.E. McHenry, IEEE Trans. Appl. Supercond. 7 (1997) 1150; S.-Y. Chu, M.E. McHenry, Electrochem. Soc. Proc. 97-2 (1997) 9.], have been characterized by both DC and AC magnetic measurements between 5 K and 108 K with a magnetic field perpendicular to the ab plane of the Bi-2223 crystal lattice. A numerical calculation indicates that the induced fields from the superconducting current loops in the separated neighboring crystals are very small and consequently can be neglected. Treating the individual crystals (73×73×1 μm3) as bar-shaped superconductors, we used a modified Bean model to determine the critical current density. For the first time, a strong temperature dependence of the current density at zero applied field is observed in these pristine single crystals with weak pinning. These then offer an excellent model system to probe the enhancements of persistent currents by means of proton irradiation.
The structure of Bi1.7Pb0.4Sr2Ca0.9Cu2O8 (Tc=93 K) was refined from x-ray single crystal diffraction data in space group A2aa, a=5.3852(9) Å, b=5.4286(9) Å, c=30.997(6) Å. For this composition, the crystal structure is free from the structural modulation connected with the presence of additional oxygen atoms in the BiO layers. The c-axis lattice parameter is slightly larger in (Bi,Pb)-2212 crystals than in Pb-free Bi-2212 crystals, but the complete structural refinement revealed an inhomogeneous redistribution of the inter-planar distances. In particular, the distance between the two neighboring BiO layers has significantly decreased in the modulation-free phase as compared to the Pb-free phase. We believe that this is a key point in understanding the widely observed reduction of the anisotropy in Bi-2212 by Pb-doping. The irreversibility line as well as the onset of the second magnetization peak in modulation-free (Bi,Pb)-2212 crystals were studied. Because of the strongly reduced value of the anisotropy, the 2D-3D crossover field value, Hcr, is significantly higher in (Bi,Pb)-2212 crsystals than in Bi-2212 crystals. As a direct consequence of the structural modifications induced by the removal of the modulation, the nature of the inter-layer coupling changes from electromagnetic in modulated Bi-2212 to Josephson in modulation-free (Bi,Pb)-2212. Annealing the (Bi,Pb)-2212 crystals under oxygen reintroduced the structural modulation.
This paper provides an update on the development, performance and application of first and second generation high temperature superconductor (HTS) wires fabricated at American Superconductor (AMSC). First generation, multifilamentary composite wire is available commercially today in different viable product forms. This conductor carries 140 × the current of copper of the same cross-section, and is robust enough to stand tough industrial requirements. Second generation HTS wires, having a coated conductor composite architecture, are under development today and achieved substantial progress recently. AMSC’s first generation wire will continue as the workhorse of the industry for the next 3–4 years while AMSC’s second generation coated conductor wire is on track to be reproducible, uniform, scalable, and low cost. This paper provides a product differentiation with a view on the application of HTS wire in the electric power sector. Basic engineering data is reviewed that shall aid the engineer in the selection of the HTS wire product.
We have investigated the vortex phase diagrams of modulation-free Bi1.7Pb0.4Sr2Ca0.9Cu2O8 crystals and Pb-free Bi2Sr2CaCu2O8+δ crystals. In (Bi,Pb)-2212 crystals, the strongly reduced anisotropy as well as the presence of a significant amount of disorder induce important differences compared to Bi-2212 crystals. We have probed the activation energies of the vortices by means of magnetic relaxation measurements, both above and below the second-magnetization peak. In the vortex phase below the peak, a power law dependence U ∝ (1/j)μ is found, with an exponent μ = 0.54 which compares favorably with the Bragg Glass prediction. In the disordered phase situated above the second-magnetization peak line, the barriers are found to slowly diverge as U ∝ ln(1/j). This suggests the existence of a glassy state in this region of the phase diagram. We have carefully measured the onset of the irreversibility in the disordered phase in both crystals. Above the 2D–3D crossover field Hcr, the resulting irreversibility lines are shown to be qualitatively described using a Lindemann approach in a 2D fluctuation regime.
We report the complete disappearance of the structural modulation in heavily lead-doped Bi2−xPbxSr2CaCu2O8+δ crystals observed by transmission electron microscopy. Crystals with a nominal lead content of x=0.8, corresponding to an effective lead content of x=0.39, yield the non-modulated phase. The superconducting properties of this modulation-free phase (β phase) have been studied and compared to those of undoped crystals displaying the modulated phase (α phase). Magnetisation measurements reveal that the irreversibility field Hirr(T) and relaxation rates are strongly improved within the β phase. Measurements of the lower critical field, Hc1, show that the anisotropy factor, ϵ, is considerably reduced in the modulation-free crystals. This is the signature of stronger coupling between CuO2 layers which in turn deeply influences the effectiveness of the pinning. These measurements explain the enhanced pinning properties in moderately Pb-doped crystals in which the α phase and β phase coexist. The enhanced pinning is not only due to the α/β interfaces, which act as effective pinning centers: the emergence of modulation-free domains, characterized by a strongly reduced anisotropy, also significantly contribute to this effect.
Single crystals of (Bi1−xPbx)2Sr2Ca2Cu3O10+δ (x = 0 and 0.16) (sizes up to 3 × 2 × 0.1 mm3) have been grown by means of a newly developed “vapour-assisted travelling solvent floating zone” technique (VA-TSFZ). Post-annealing under high pressure of O2 (up to 10 MPa at T = 500 °C) was applied to enhance Tc (up to 111 K) and improve the homogeneity of the crystals (ΔTc ⩽ 1 K). The structure of both Pb-free and Pb-doped Bi-2223 was refined for the first time from single crystal X-ray diffraction (XRD) data. The unit cell of the average structure is pseudo-tetragonal with a = 5.4210(7), b = 5.4133(6) and c = 37.010(7) Å, and a = 5.395(1), b = 5.413(1) and c = 37.042(11) Å, for the Pb-free and the Pb-doped phase, respectively. An incommensurate modulation in the direction of one of the short cell vectors has been defined (q ∼ 0.21 a∗), however, the structure can be conveniently described in a supercell with a fivefold volume (a = 27.105(4) Å). With respect to the “non-modulated” structure, one additional oxygen atom for ten initial O was found to be inserted into the BiO layers. The superconducting anisotropy of Bi-2223 was found to be ∼50, from measurements of the lower critical field. The anisotropy of Bi-2223 is significantly reduced compared to that of Bi-2212, and this accounts for the enhanced irreversibility fields in Bi-2223. Furthermore, Bi-2223 has a higher critical current density, and a reduced magnetic relaxation rate compared to Bi-2212, which are both signatures of more effective pinning in Bi-2223 due to its reduced anisotropy.
The growth of Pb-free Bi2Sr2Ca2Cu3O10+delta (Bi-2223) single crystals has been investigated using the travelling solvent floating zone technique under mixed gas flow of argon and oxygen. Slow growth rates of 0.20, 0.10, 0.06 and 0.04 mm/h were applied to four growth runs. Nearly single-phase Bi-2223 crystals sized up to 10 x 6 x 0.5 mm(3) were obtained using a slow growth rate of 0.04 mm/h and subsequent annealing. The crystals were characterized by energy dispersive X-ray, X-ray diffraction (XRD), transmission electron microscopy, magnetic susceptibility and resistivity measurements. It is found that the growth rate affects the phase formation of Bi-2223 crystals. Both XRD and magnetic susceptibility measurements show that the as-grown crystals obtained at a slow growth rate of 0.04 mm/h consist of >90% Bi-2223 phase, whereas as-grown crystals obtained at rates of 0.10 and 0.20 mm/h contain predominantly Bi-2212, Ca2CuO3 and a small quantity of Bi-2223 phase. Post-annealing experiments were carried out at 500-850 degreesC for 120-500 h in an effort to improve the crystal quality with respect to phase purity and oxygen homogeneity. A phase-transformation process from Bi-2212 to Bi-2223 was observed. The results of XRD and susceptibility measurements show that the relative fraction of the Bi-2223 phase increases upon increased annealing temperature and/or prolonged annealing time while the Bi-2212 phase diminishes gradually, resulting in crystals that were of 98-99% Bi-2223 phase. Such a phase transformation from Bi-2212 into Bi-2223 might be explained via a layer-intercalation mechanism. The refinement results of XRD data show that pure-phase Bi-2223 crystals have orthorhombic symmetry with lattice parameters of a = 5.408(2) Angstrom, b = 5.413(7) Angstrom, and c = 36.868(1) Angstrom. Narrow full width at half maximum of 0.16-0.20degrees determined from X-ray rocking curve measurements demonstrates the high crystallinity of Bi-2223 crystals. The superconducting transition temperature T, increases from 102 K for as-grown crystals to 110 K for crystals annealed at 850 degreesC for 500 h in O-2 flow. The in-plane and out-of-plane resistances as a function of temperature measured on annealed crystals show that the general features of the resistivity of Bi-2223 crystals are similar to those of Bi-2212 crystals. (C) 2002 Elsevier Science B.V. All rights reserved.
Crystal growth and superconducting properties of ${rm Bi}_{2}{rm Sr}_{2}{rm Ca}_{2}{rm Cu}_{3}{rm O}_{10+delta}$ (Bi2223) single crystals
- K Shimizu
- T Okabe
- S Horii
- K Otzschi
- J Shimoyama
- K Kishio
Single crystals of triple-layered cuprates ${\rm Bi}_{2}{\rm Sr}_{2}{\rm Ca}_{2}{\rm Cu}_{3}{\rm O}_{10+\delta}$ : Growth, annealing and characterization
- B Liang
- C T Lin
- P Shang
- G Yang
Single-crystal growth of ${\rm Bi}_{2}{\rm Sr}_{2}{\rm Ca}_{2}{\rm Cu}_{3}{\rm O}_{10+\delta}$ (Bi-2223) by TSFZ method
- T Fujii
- T Watanabe
- A Matsuda
Phase evolution, structural and superconducting properties of Pb-free ${\rm Bi}_{2}{\rm Sr}_{2}{\rm Ca}_{2}{\rm Cu}_{3}{\rm O}_{10+\delta}$ single crystals
- B Liang
- C Bernhard
- T Wolf
- C T Lin
Lower critical field ${\rm H}_{{\rm c}1}$ and barriers for vortex entry in ${\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{8+}$ crystals
- M St
- R Frassanito
- M Saalfrank
- A C Mota
- G Blatter
- V N Zavaritsky
- T W Li
- P H Kes
Lower critical field