Sr2 Ca2 Cu3 Oy Research Articles

Mass spectrometric studies of laser ablated plume from a superconducting material

The ionic species present in the laser ablated plume from the surface of the Bi1.6Pb0.4Sr2Ca2Cu3 Oy superconducting target have been investigated using a non-commercial laboratory developed linear time-of-flight (TOF) mass spectrometer. The recorded TOF mass spectra reveal the presence of all the atomic species of the target material, monoxide and cluster ions. The occurrence of clusters in the mass spectra is the evidence of aggregation processes at higher laser fluence. The dependence of the ionic yield of the species has been studied using the fundamental (1064 nm), second harmonic (532 nm) and fourth harmonic (266 nm) of a Nd:YAG laser. The maximum ionization of the species present in the plume is observed at 266 nm even at lower laser fluence. The effect of the laser fluence on the total and individual ionic yields of the ablated species is also presented.

Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconductors

The compositional dependence of elastic properties of Al3+-substituted Bi(Pb)-2223 superconducting system with the general formula Bi1.7−x AlxPb0.3Sr2Ca2Cu3 Oy (x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous metal mixture rule for estimating elastic constants and transition temperature has been tested.

High- Tc phase obtained in the Pb/Sb doped Bi–Sr–Ca–Cu–O system

Partial replacement of Bi by Pb and Sb produces materials of high- T c pure phase, with antimony playing an important role in accelerating the formation of the phase with the higher superconductive transition in the Bi–Sr–Ca–Cu–O system. The influence of the antimony precursors on the superconducting phases mechanism formation was examined. Using a solid state reaction route, two nominal compositions Bi 1.6Pb 0.3Sb 0.1Sr 2Ca 2Cu 3Oy and Bi 1.6Pb 0.4Sb 0.1Sr 2Ca 2Cu 4Oy were investigated. The sources of antimony were Sb 2O 3, αSb 2O 4 and a prepared mixture Bi 1.9Sb 0.1O x . The mechanism formation of the phases upon annealing was investigated using X-ray diffraction and simultaneous thermal analysis. Electrical properties of the obtained materials were evaluated. The presence of the antimony ions determined a higher reactivity of the system as well as the promotion of the superconducting high- T c phase enhancement.

Synthesis, magnetic and structural studies of the 110 K phase of Bi1.6 Pb0.4 Sr2 Ca2 Cu3 Oy high Tc superconductor

Characterization of samples of Bi1.6 Pb0.4 Sr2 Ca2 Cu3 Oy composition through XRD, SEM, EDAX, EPR, microwave absorption(MA), resistivity(ϱ(T)) and ac-susceptibility(χac) measurements has shown that the material consists of a single phase. Temperature dependence of imaginary part of χac exhibits a sharp peak at the transition temperature(Tc) whereas the real part undergoes a sharp diamagnetic transition. The width(ΔTc) estimated from the plot of dϱ/dT vs temperature is 3K. The field dependence of MA has shown hysteresis. The effect of field cooling(FC) and zero field cooling (ZFC) on low-field dependent MA reveals that the area of hysteresis loop of the FC sample has decreased significantly as compared to that the ZFC.

Effect of V, Nb, and Ta Doping on the 2223 Phase Formation and the Crystal Structure in the BiSrCaCuO System

X-ray diffraction and electrical and diamagnetic analyses revealed that the 2223 phase was significantly enhanced by high-valence cation (V5+, Nb5+, Ta5+, etc.) doping in BiSrCaCuO samples. The optimum nominal composition was Bi1.6M0.4Sr2Ca2Cu3 Oy(M = high-valence cations) for all three elements. A quasi-high-valence peak of Cu2p3/2 (∼534.5 eV) has been observed. A reversible reaction, Bi3+⇆annealedquenched Bi5+ + Bi+, was also encountered in the sample doped with Nb5+. The effects of doping high-valence cations on the high-Tc phase formation and the crystal structure are two-fold: (1) The high-valence cation substitution for the fourfold-coordinated Cu site in the CuO2 sheet strengthens the coupling among the Ca-CuO2-Ca layers of the 110 K phase, and (2) the cations incorporated into the Bi-O layers increase the oxygen bonding, which is beneficial for the formation of the Aurivillius-type structures and stabilizes the structure of the 2223 phase. We argue that the beneficial effect for promoting the formation of the 2223 phase might be a general property of doping with high-valence cations.

17O Knight shifts of the various types of CuO2 planes in Bi-cuprates high-Tc superconductors

A 17 O NMR study has been performed on a 17 O enriched powder sample of (Bi, Pb)2 Sr2 Ca2 Cu3 Oy , also called n = 3 phase (with Tc = 110K) which belongs to the Bi-based superconductors family (Bi, Pb)2 Sr2 Can-1 Cun O2n+4 The n = 3 compound which contains in its unit cell two types of CuO2 planes (labelled type I and II), Is compared to the n = 2 compound where only one type of CuCO2 planes (type I) is present. 17 O Knight shift measurements versus temperature, in the normal phase, have allowed us to evidence the distinct behaviours of the two types of planes present in the n = 3 compound. The results are consistent with the existence of stronger electron correlations, or smaller charge carrier density in the type II planes.

錯体重合法によるＢｉ‐Ｐｂ‐Ｓｒ‐Ｃａ‐Ｃｕ‐Ｏ超伝導体の合成

Superconducting Bi-Pb-Sr-Ca-Cu-O ceramics have been synthesized by the polymerized complex method at the Bi1.8Pb0.2Sr2Ca2 Cu3Oy (A), Bi1.6Pb0.4Sr2Ca2Cu3<Oy (B) and Bi1.68Pb0.32Sr1.75Ca1.82Cu2.83Oy (C) compositions. The present technique offers more convenient and easier fabrication of highly pure and homogeneous (Bi, Pb)-2223 superconductors compared with other elaborate preparation procedures based on wet-chemical techniques. Complex susceptibility measurements show that Tc(onset) of the (Bi, Pb)2223 phase remains almost constant at 108 K independent of the compositions. However, the intergranular coupling between the active (Bi, Pb)-2223 superconducting grains was very dependent on the compositions as well as on the sintering period.

Superconductivity studies on the MTlSrCaCuO (M = Rate Earth, Sc, Y, Pb, Bi, Th) system

Studies on MTl2 Sr2 Ca2 Cu3 Oy (M = Rare Earth, Y, Sc, Pb, Bi and Th) show that superconductivity in the range 40–77K can be achieved in this system depending on the M-ion. The minimum amount of rare earth required to show a Tc ∼ 70K appears to be 25 mole percent. X-ray studies confirm the single phase material responsible for high Tc superconductivity to be 1212 type. It appears that Pb, Bi and Th substitute at the Tl- site whereas the rare earths, Y and Sc prefer the Ca − site.

Chemical Preparation of Superconducting Oxides Using Conventional Chelating Agents

ABSTRACTSamples of Bi1.4Pb0.6Sr2 Ca2Cu3Oy were prepared by sol-gel technique. The formation of polymeric chelate was made possible by oxalic acid in which metal cations are homogeneously distributed. The functional groups in the chelating agent determine the cation absorption rate that pH value is no more critical. XRD and SQUID showed that the compound has a nearly pure 2223 phase and Tc was measured at 110 K. The synthesis is reproducible and the process is amenable for scaling up.

Electron diffraction studies of the incommensurate modulations in (Bi-Pb)-Sr-Ca-Cu-O superconductors

We have studied the incommensurate modulations of lead free Bi-Sr-Ca-Cu-O and lead substituted (Bi-Pb)-Sr-Ca-Cu-O superconductors at different temperatures between 110 K and 300 K. The modulations are temperature independent in this interval. The incommensurate modulations of two lead substituted compounds of nominal compositions Bi1.8Pb0.2Sr2Ca2Cu3Ox and Bi1.5Pb0.5Sr 2Ca2Cu3Oy have been observed at room temperature. The Pb modulation value decreases with a higher lead concentration.

Preparation and characterization of superconducting phases in the Bi(Pb)-Sr-Ca-Cu-O system

The superconductive properties in the Bi(Pb)-Sr-Ca-Cu-O system with nominal composition of Bi2−x Pbx Sr2 Ca2 Cu3 Oy (x=0, 0.2, 0.4, and 0.6) and annealed at 860 °C for 240 h were studied using dc resistivity and ac susceptibility measurements. For x=0.2 and 0.4, the bulk zero resistivity temperatures were found to be ∼103 K. For x=0 and 0.6, these temperatures were found to be ∼73–75 K. The ac susceptibility data show enrichment of the volume fraction of the high-Tc phase in compositions with x=0.2 and 0.4. Tc of this phase is constant at 107 K for all values of x. The enhancement of the bulk zero resistivity temperature for x=0.2 and 0.4 is due to the improved intergranular coupling of the high-Tc phase, although the resulting weak-link behavior reflects a low current carrying capacity in these materials. The presence of the low-Tc phase (∼65 K) is still visible in the susceptibility data. For x=0.6, the intergranular coupling of the high-Tc phase is almost destroyed; however, the coupling of the low-Tc phase is better than when x=0. Powder x-ray diffraction and scanning electron microscopy data show the formation of large grains of the calcium plumbate, Ca2PbO4 phase with increasing Pb up to x=0.6. The large grains of the Ca2 PbO4 phase may incorporate other impurity phases within it when x=0.6, cleaning up the remaining grain boundaries, thereby improving the intergranular coupling within this material. Energy dispersive x-ray analysis indicates that some Pb is incorporated into the structure of both superconducting phases.