Stabilization of high T(sub c) phase in bismuth cuprate superconductor by lead doping

Science.gov (United States)

Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

1990-01-01

It has widely been ascertained that doping of lead in Bi:Sr:Ca:Cu:O systems promotes the growth of high T(sub c) (110 K) phase, improves critical current density, and lowers processing temperature. A systematic investigation is undertaken to determine optimum lead content and processing conditions to achieve these. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance-temperature (R-T) measurements and x ray diffraction (XRD) to determine the zero resistance temperature, T(sub c)(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T(sub c) single phase with highly stable superconducting properties.

Some crystal chemistry of (Ln,Ce)2CuO4-δ superconductors

International Nuclear Information System (INIS)

Goodman, P.; Keating, A.; Myhra, S.; White, T.J.

1989-01-01

Compounds of the form (Ln, Sr, Ce) 2 CuO 4-δ (Ln = rare earth element) crystallise as the Nd 2 CuO 4 structure type, K 2 NiF 4 structure type or perfectly and imperfectly ordered intergrowths of these parent structures. These structurally similar phases exhibit superconductivity in which the charge carriers are holes (in Sr-doped material) or electrons (in Ce doped material). In this study, X-ray Photoelectron Spectroscopy (XPS) and High Resolution Electron Microscopy (HREM) were used to investigate the charge balancing mechanisms operating in each superconducting regime and the structural changes accompanying compositional variation. It was found that under slightly reducing conditions charge coupled cation substitutions predominate, whilst at low pO 2 ( -5 atm) perfectly ordered oxygen superlattices form. The structural and electronic changes which accompany deoxygenation were observed in situ during XPS and HREM observations. 29 refs., 8 figs., 3 tabs

Tl Cuprate Superconductors Studied by XPS

Energy Technology Data Exchange (ETDEWEB)

Vasquez, R. P. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099 (United States); Siegal, M. P. [Sandia National Laboratories, Albuquerque, NM 87185-1421 (United States); Overmyer, D. L. [Sandia National Laboratories, Albuquerque, NM 87185-1421 (United States); Ren, Z. F. [Department of Chemistry, State University of New York, Buffalo, NY 14260-3000 (United States); Lao, J. Y. [Department of Chemistry, State University of New York, Buffalo, NY 14260-3000 (United States); Wang, J. H. [Department of Chemistry, State University of New York, Buffalo, NY 14260-3000 (United States)

1999-07-01

XPS measurements on epitaxial thin films of the Tl cuprate superconductors Tl2Ba2CaCu2O8, Tl2Ba2Ca2Cu3O10, and Tl0.78Bi0.22Ba0.4Sr1.6Ca2Cu3O9-{delta} are presented. These data, together with previous measurements in this lab on Tl2Ba2CuO6-{delta} and TlBa2CaCu2O7-{delta}, comprise a comprehensive data set for comparison of Tl cuprates in which the number of Tl-O and Cu-O layers, and hence the chemical and electronic properties, vary. (c) 2000 American Vacuum Society.

Method for making low-resistivity contacts to high T/sub c/ superconductors

International Nuclear Information System (INIS)

Ekin, J.W.; Panson, A.J.; Blankenship, B.A.

1988-01-01

A method for making low-resistivity contacts to high T/sub c/ superconductors has been developed, which has achieved contact surface resistivities less than 10 μΩ cm 2 at 76 K and does not require sample heating above ∼150 0 C. This is an upper limit for the contact resistivity obtained at high current densities up to 10 2 --10 3 A/cm 2 across the contact interface. At lower measuring current densities the contact resistivities were lower and the voltage-current curve was nonlinear, having a superconducting transition character. On cooling from 295 to 76 K, the contact resistivity decreased several times, in contrast to indium solder contacts where the resistivity increased on cooling. The contacts showed consistently low resistivity and little degradation when exposed to dry air over a four-month period and when repeatedly cycled between room temperature and 76 K. The contacts are formed by sputter depositing a layer of a noble metal-silver and gold were used-on a clean superconductor surface to protect the surface and serve as a contact pad. External connections to the contact pads have been made using both solder and wire-bonding techniques

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

International Nuclear Information System (INIS)

Le Noc, L.; Trokiner, A.; Schneck, J.; Pougnet, A.M.; Mellet, R.; Primot, J.; Savary, H.

1992-01-01

A 17 O NMR study has been performed on a 17 O enriched powder sample of (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O y , also called n=3 phase (with Tc=110K) which belongs to the Bi-based superconductors family (Bi,Pb) 2 Sr 2 Ca n-1 Cu n O 2n+4 . The n=3 compound which contains in its unit cell two types of CuO 2 planes (labelled type I and II), is compared to the n=2 compound where only one type of CuO 2 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. 14 refs., 3 figs

Giant T{sub c} shift in HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}} superconductors due to Hg-Tl exchange

Energy Technology Data Exchange (ETDEWEB)

Gapud, A.A.; Wu, J.Z.; Kang, B.W.; Yan, S.L.; Xie, Y.Y. [Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045-2151 (United States); Siegal, M.P. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)

1999-01-01

The irreversibility lines of epitaxial thin films of HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}, whether deduced from field-induced magnetoresistive broadening or onset of nonhysteretic magnetization, were found to coincide when plotted against reduced temperature, showing the same exponential-decay temperature behavior for T/T{sub c}{lt}0.8 and power-law behavior for T/T{sub c}{gt}0.8 (where T{sub c} is zero-field, zero-resistivity critical temperature). These results indicate that replacing Tl with Hg has no noticeable effect on the anisotropy and suggests that T{sub c} is not determined by anisotropy. {copyright} {ital 1999} {ital The American Physical Society}

Magnetic-field-induced spin excitations and renormalized spin gap of the underdoped La1895Sr0105CuO4 superconductor

DEFF Research Database (Denmark)

Chang, J.; Schnyder, A.P.; Gilardi, R.

2007-01-01

High-resolution neutron inelastic scattering experiments in applied magnetic fields have been performed on La1.895Sr0.105CuO4 (LSCO). In zero field, the temperature dependence of the low-energy peak intensity at the incommensurate momentum transfer Q(IC)=(0.5,0.5 +/-delta,0),(0.5 +/-delta,0.5,0) ...

Determination of oxygen content in high T/sub c/ superconductors by a charged particle activation method

International Nuclear Information System (INIS)

Tao, Z.; Alburger, D.E.; Jones, K.W.; Yao, Y.D.; Kao, Y.H.

1988-01-01

A new method for determining the oxygen content in high T/sub c/ superconductors has been demonstrated using a charged particle activation technique. This method allows a measurement of the concentration of 16 O atoms in the superconducting material by detection of the 17 F produced with the 16 O(d,n) 17 F nuclear reaction. By way of example, this technique is applied to the determination of oxygen content in a series of high T/sub c/ Y-Ba-Cu-O samples in which the stoichiometry is varied by reducing the copper concentration. The stabilized oxygen content shows a nonlinear dependence on the copper deficiency in these specimens

Improvement of high T{sub c} superconductor by near-optimum pinning centers created by high Z, high-energy ions

Energy Technology Data Exchange (ETDEWEB)

Weinstein, Roy, E-mail: Weinstein@uh.edu [Texas Center for Superconductivity, Physics Department, 632 Science and Research Bldg. 1, University of Houston, Houston, TX 77204-5005 (United States); Sawh, Ravi-Persad; Parks, Drew; Mayes, Billy [Texas Center for Superconductivity, Physics Department, 632 Science and Research Bldg. 1, University of Houston, Houston, TX 77204-5005 (United States)

2012-02-01

Damage tracks left by high Z, high-energy ions in high temperature superconductor (HTS) can serve the need to pin in place the magnetic field quanta. Such pinning centers (PCs) can serve to dramatically increase the critical current density, J{sub c}. Specific energy loss, S{sub e}, which is effective in the YBCO superconductor (YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}) lies in the range 0.7 Less-Than-Or-Slanted-Equal-To S{sub e} Less-Than-Or-Slanted-Equal-To 3.5 keV/A. At 77 K, a sharp peak in J{sub c} occurs at S{sub e} {approx} 2.1 keV/A, for fluences of 10{sup 12} ions/cm{sup 2}, where record in-field J{sub c} is achieved in large-grain YBCO. For example, J{sub c} = 340 kA/cm{sup 2} at 77 K, applied field of 1 T. At closely similar conditions record in-field J{sub c} is achieved in thick coated conductor, e.g., J{sub c} = 543 kA/cm{sup 2} at 77 K, 1 T. When corrected to the optimum S{sub e}, this J{sub c} increases to 770 kA/cm{sup 2}. These near-optimum PCs have very small diameter of damage (d{sub d} {approx} 6.6 nm) close to the value, predicted theoretically. However, they are very discontinuous, whereas theory predicts that continuous columnar PCs are the best to obtain high J{sub c}. We find that the advantages of discontinuous PCs at S{sub e} = 2.1 keV/A, are (a) a factor of 12 less damage to the HTS (resulting in improved percolation and T{sub c}) and (b) entanglement of fluxoids (even for parallel PCs). This results in five times higher J{sub c} than can be achieved with continuous columnar PCs. In large-grain HTS, these pinning centers increase J{sub c} by a factor of 17, indicating that the dominant reduction of J{sub c} in large-grain HTS is due not to weak links, voids, non-optimum oxygenation, etc., but to a dearth of pinning centers.

Can positron 2D-ACAR resolve the electronic structure of high-Tc superconductors

International Nuclear Information System (INIS)

Chan, L.P.; Lynn, K.G.; Harshman, D.R.

1992-01-01

In this paper, the authors examine the ability of the positron Two-Dimensional Angular Correlation Annihilation Radiation (2D-ACAR) technique to resolve the electronic structures of high-T c cuprate superconductors. Following a short description of the technique, discussions of the theoretical assumptions, data analysis and experimental considerations, in relation to the high-T c superconductors, are given. The authors briefly review recent 2D-ACAR experiments on YBa 2 Cu 3 O 7-x , Bi 2 Sr 2 CaCuO 8+δ and La 2-x Sr x CuO 4 . The 2D-ACAR technique is useful in resolving the band crossings associated with the layers of the superconductors that are preferentially sampled by the positrons. Together with other Fermi surface measurements (namely angle-resolved photoemission), 2D-ACAR can resolve some of the electronic structures of high-T c cuprate superconductors

Synthesis of CuO nanoflower and its application as a H2O2 sensor

Indian Academy of Sciences (India)

Administrator

CuO; nanoflowers; electrochemical; H2O2. 1. Introduction. Cupric oxide (CuO) is an important transition metal oxide ... several high temperature superconductors and giant mag- ... precipitate was washed with ethanol and distilled water.

Contact spectroscopy of high-temperature superconductors. Review

International Nuclear Information System (INIS)

Yanson, I.K.

1991-01-01

We have attempted to systematize the research of high temperature superconductors by means of tunneling and point-contact spectroscopy. The theoretical grounds of the methods are briefly described. The deviations of current-voltage characteristics from ordinary superconductors are considered. The properties of point contacts with direct energy gap measurfements and the fine structure of derivatives of i(v) curves at the overlap energies are reviewed for the high-T c La 2-x Sr x CuO 4 materials

Chemical stability of high-temperature superconductors

Science.gov (United States)

Bansal, Narottam P.

1992-01-01

A review of the available studies on the chemical stability of the high temperature superconductors (HTS) in various environments was made. The La(1.8)Ba(0.2)CuO4 HTS is unstable in the presence of H2O, CO2, and CO. The YBa2Cu3O(7-x) superconductor is highly susceptible to degradation in different environments, especially water. The La(2-x)Ba(x)CuO4 and Bi-Sr-Ca-Cu-O HTS are relatively less reactive than the YBa2Cu3O(7-x). Processing of YBa2Cu3O(7-x) HTS in purified oxygen, rather than in air, using high purity noncarbon containing starting materials is recommended. Exposure of this HTS to the ambient atmosphere should also be avoided at all stages during processing and storage. Devices and components made out of these oxide superconductors would have to be protected with an impermeable coating of a polymer, glass, or metal to avoid deterioration during use.

Nernst effect of Ni-doped NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} and transport properties in UPt{sub 2}Si{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Johannsen, Niko

2008-05-15

In this thesis, the Nernst effect in high-temperature superconductors is investigated. Large Nernst voltages were found to survive up to temperatures that reach far out of the superconducting phase. This was extensively studied thereafter in wide doping range of the high-T{sub c}'s. We were able to significantly expand these studies by tuning T{sup *} and T{sup {nu}} independently. This was done by inducing Ni ions into the CuO planes of NdBa{sub 2}{l_brace}Cu{sub 1-y}Ni{sub y}{r_brace}{sub 3}O{sub 7-{delta}} which allowed to study the Nernst effect in a wide parameter range. This is done on one hand in dependence of the oxygen content which varies the charge carrier concentration. On the other hand, the Ni concentration is varied from 0% to 12%, thereby enhancing T{sup *} and simultaneously suppressing T{sub c} with increasing concentrations. The temperatures to which the anomalous Nernst signal is detectable is the onset temperature T{sup {nu}}. The goal of this work was to find out whether T{sup {nu}} follows T{sub c} or T{sup *}. The onset temperatures of the anomalous Nernst signals are determined as the slightest detectable deviation from the quasiparticle background above T{sub c}. In the second part of this work, the Nernst effect and other transport properties of UPt{sub 2}Si{sub 2}, including electrical ones such as the resistivity and the Hall effect and thermal ones, as the thermal conductivity, the thermopower and the Righi-Leduc effect were investigated. (orig.)

Enhanced T{sub c} in a dual-layered molecular superconductor

Energy Technology Data Exchange (ETDEWEB)

Souza, Mariano de; Lang, Michael [Physikalisches Institut, J.W. Goethe-Universitaet, SFB/TR49, D-60438 Frankfurt/M (Germany); Wiehl, Leonor [Institut fuer Geowissenschaften, J.W. Goethe-Universitaet, D-60438 Frankfurt/M (Germany); Schlueter, John A. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2011-07-01

We have revisited the structural and electronic properties of the filamentary organic superconductor (BEDT-TTF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), first synthesized in 1994. Detailed structural investigations reveal that the BEDT-TTF molecules are arranged in two distinctly different packing motifs, {kappa} and {alpha}', which alternate from layer to layer. This molecule-based superconductor with dual BEDT-TTF packing motifs has a T{sub c} five times higher than that of its polymorph that contains only {kappa}-type packing. Using the established empirical correlations between the bond lengths (C-S and C=S) and the oxidation state of the BEDT-TTF molecule, we have found that there is a uniform charge distribution in the {kappa}-layers (corresponding to an oxidation state of +0.5 for all BEDT-TTF molecules), whereas in the {alpha}'-layer, half of the molecules are nearly fully oxidized to +1, while the other half are close to neutral, resulting in a charge-ordered neutral layer. These findings indicate that this material can be considered as a promising candidate for a distinctly two-dimensional superconductor.

Atomic ordering of the fluorine dopant in the $HgBa_{2}CuO_{4+\\delta}high-T_{c}$ superconductor

CERN Document Server

Correia, João Guilherme; Araújo, João Pedro; Bordet, P; Haas, Heinz; Le Floc'h, S; Lopes, A M L; Rita, E; Carvalho-Soares, João

2005-01-01

Lattice sites and collective ordering of fluorine atoms in oxygen- reduced samples of HgBa/sub 2/CuO/sub 4/ were investigated with the perturbed angular correlation technique by measuring the electric field gradients induced at /sup 199m/Hg nuclei. The experimental data were interpreted with the help of ab initio calculations of charge distributions for different fluorine configurations in Hg/sub m/Ba /sub 2m/Cu/sub m/O/sub 4m/F/sub n/, supercells. Internal parameters were allowed to relax, to cancel residual atomic forces due to the dopant. The experimental results show clearly that fluorine occupies only the center of the mercury mesh. For a fluorine content delta F>~0.35 the best agreement with theoretical data is obtained under the assumption that fluorine shows a tendency toward ordering along interstitial rows parallel to a, b. In conformity with experimental data from diffraction techniques the calculations show elongations of the O(2)-Hg-O(2) dumbbell and barium shifts towards the fluorine atoms as ef...

Conductivity fluctuation in the high temperature superconductor with planar weight disparity Y{sub 0.5}Sm{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}}

Energy Technology Data Exchange (ETDEWEB)

Barrera, E.W.; Rojas Sarmiento, M.P.; Rincon, L.F.; Landinez Tellez, D.A.; Roa-Rojas, J. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 14490, Bogota DC (Colombia)

2007-07-01

The synthesis of the Y{sub 0.5}Sm{sub 0.5}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}} superconducting material by the standard solid state reaction is reported. DC resistivity measurements reveal the improvement of the critical temperature (T{sub c}) when substitution of exact 50-50 mix of Yttrium and Samarium is performed. A bulk T{sub c} = 101 K was determined by the criterion of the maximum in the temperature derivative of electrical resistivity. Structure characterization by means the x-ray diffraction technique shows the crystalline appropriated distribution of Yttrium and Samarium to create substantial planar weight disparity (PWD) in alternating layers. This PWD increases T{sub c} in copper-oxide superconductors. In order to examine the effect of PWD on the pairing mechanism close to T{sub c}, conductivity fluctuation analysis was performed by the method of logarithmic temperature derivative of the conductivity excess. We found the occurrence of Gaussian and genuinely critical fluctuations. Our results are in agreement with reports on YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}, but an enhancement of the Gaussian fluctuation regimes was experimentally detected as a result of the PWD. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed by using the Aslamazov-Larkin theory. The genuinely critical exponent is interpreted by the 3D-XY model as corresponding with the dynamical universality class of the E-model. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Quantum Spin Models for Copper Oxide Chains in High-T{sub c} Superconductors

Energy Technology Data Exchange (ETDEWEB)

Haugerud, H.

1996-12-31

This doctoral thesis presents some of the most important features of high temperature superconductors, emphasizing the properties of YBa{sub 2}Cu{sub 3}O{sub 6+x} (YBCO). The family of Hubbard-like models is considered and a simplified version of the Emery model derived. This model is applied to fermions on a cyclic chain and solved analytically in the strong correlation limit. For realistic model parameter values the effects of an external magnetic field is investigated by numerical diagonalization. Applying the Emery model to finite cyclic Cu-O chains it is shown that the behaviour of the chains is typical for a 1D Fermi-liquid. The relatively small difference between the values of the local charge and the local magnetic moment indicates that the degree of correlation in this system is very high. The ground state of the Emery model is shown to be antiferromagnetic for half and quarter filling, resembling the ground state of the Heisenberg model. The role of the ensemble of Cu-O chain fragments of the oxygen deficient planes of YBCO is addressed. By applying the Emery model to short Cu-O chains and calculating the free energy of the chains, the parameters of an Ising like lattice gas model are estimated. Several thermodynamical quantities are calculated by applying Monte Carlo technique to the model. The charge transfer from the chains to the planes is shown to correspond to the measured values of T{sub c}. The phase diagram and the average chain length agree well with experiments. The model is also capable of explaining the behaviour of the REBCO series of superconductors, where RE are various rare earth ions. A framework for simultaneously visualizing and computing numerical quantities from lattice simulations is presented and illustrated. 195 refs., 69 figs., 4 tabs.

The local structure of high-temperature superconductors

International Nuclear Information System (INIS)

Mustre de Leon, J.; Conradson, S.D.; Bishop, A.R.; Raistrick, I.D.

1992-01-01

We show how x-ray absorption fine structure (XAFS) has been successfully used in the determination of the local crystal structure of high-temperature superconductors, with advantages over traditional diffraction techniques. We review the experimental results that yielded the first evidence for an axial-oxygen-centered lattice instability connected with the superconductivity transition. The interpretation of this instability in terms of a dynamical tunneling model suggests the presence of polarons in these materials. XAFS on Tl 2 Ba 2 CuO 6 and other Tl-based superconductors indicate the presence of local instabilities in the CuO 2 planes of these materials, in addition to axial-oxygen instabilities

Levitation force and magnetization in bulk and thin film high T{sub c} superconductors

Energy Technology Data Exchange (ETDEWEB)

Riise, A.B

1998-04-01

The authors present high-resolution measurements of the repulsive vertical force and its associated stiffness between a Nd-B-Fe magnet and a YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductor in cylindrical geometry. The results are compared with theoretical predictions. The calculations are based on a model in which the superconductor is assumed to be either a sintered granular material or consisting of grains embedded in a nonactive matrix so that only intragranular currents are important. The critical state model is applied to each grain individually and closed form expressions for both vertical force F{sub z} and stiffness are obtained in a configuration with cylindrical symmetry. The model explains all features of the experimental results in a consistent way. A good quantitative agreement has been obtained using only three adjustable parameters. Several central aspects of the phenomenon of magnetic levitation with high-T{sub c} superconductors are presented. High-resolution measurements are made of the repulsive vertical force and its associated stiffness as well as the horizontal stabilizing force and the stiffness governing lateral vibrations. The results obtained at 77 K using a granular YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} sample and Nd-Fe-B magnet in a rectangular levitation configuration are compared with theoretical predictions. The calculations, which are based on the critical state model with the assumption that it applies to the grins individually, give closed-form expressions for all the measured quantities. It is concluded that the present model explains all features of the observations in a consistent way. Using only three adjustable parameters a good agreement exists also at a quantitative level. Experimental studies and theoretical modelling of the levitation force on a permanent magnet placed above a superconducting thin film are offered. It is shown that measurements of the levitation force is a simple and precise method to determine the

High T[sub c] superconductivity in YBa[sub 2]Cu[sub 3]O[sub 7-x] studied by PAC and PAS

Energy Technology Data Exchange (ETDEWEB)

Zhu Shengyun (China Inst. of Atomic Energy, Beijing, BJ (China)); Li Anli (China Inst. of Atomic Energy, Beijing, BJ (China)); Zheng Shengnan (China Inst. of Atomic Energy, Beijing, BJ (China)); Huang Hanchen (China Inst. of Atomic Energy, Beijing, BJ (China)); Li Donghong (China Inst. of Atomic Energy, Beijing, BJ (China)); Din Honglin (China Inst. of Atomic Energy, Beijing, BJ (China)); Du Hongshan (China Inst. of Atomic Energy, Beijing, BJ (China)); Sun Hancheng (China Inst. of Atomic Energy, Beijing, BJ (China))

1993-11-01

High T[sub c] superconductivity has been investigated in YBaCuO by both perturbed angular correlation and positron annihilation spectroscopy techniques as a function of temperature from 77 to 300 K. An abrupt change has been observed in the positron lifetime and Doppler broadening and the electric field gradient and its asymmetry parameter across T[sub c], indicating a transition of two- to one-dimensional Cu-O-Cu chain structure and a charge transfer from CuO layers to CuO chains. An anomaly of the normal state has been demonstrated around 125 K, which is attributed to the structural instability. (orig.)

Enhancement in the high-T{sub c} phase of BSCCO superconductors by Nb addition

Energy Technology Data Exchange (ETDEWEB)

Soezeri, Hueseyin [TUBITAK-UME, National Metrology Institute, PO Box 54 TR-41470, Gebze Kocaeli (Turkey); Ghazanfari, Nader [Middle East Technical University, Physics Department, 06531 Ankara (Turkey); Oezkan, Huesnue [Middle East Technical University, Physics Department, 06531 Ankara (Turkey); Kilic, Ahmet [Middle East Technical University, Physics Department, 06531 Ankara (Turkey)

2007-06-15

Pure and Nb{sub 2}O{sub 5} added Bi{sub 1.6}Pb{sub 0.4}Nb{sub x}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {delta}} superconductors (x varies up to 0.30) were synthesized by the solid state reaction method. Structural and superconducting properties of the samples were investigated. The fraction of the high-T{sub c} phase (2223) increases with Nb addition up to x = 0.10, for which a nearly single 2223 phase was obtained. The critical temperature of the samples increases from 96 to 104 K with doping up to x = 0.20 and a further increase in Nb decreases the T{sub c} sharply. Similarly, there is a considerable enhancement in the critical current density (j{sub c}) of the samples in the same doping range. Both AC susceptibility and transport measurements showed that the optimum Nb concentration is x = 0.20. The out-of-phase component of the AC susceptibility measurements showed that inter-grain coupling was enhanced up to the same doping level. Nb additions above x = 0.30 decrease the fraction of the high-T{sub c} phase and degrade the superconducting properties. Present measurements indicate that x = 0.20 is the optimum Nb concentration in the BSCCO superconductor to enhance phase purity, inter-grain coupling and superconducting parameters (T{sub c} and j{sub c})

Microwave study of the high-T/sub c/ superconductor La/sub 1.8/Sr/sub 0.2/CuO4

International Nuclear Information System (INIS)

Poirier, M.; Quirion, G.; Poeppelmeier, K.R.; Thiel, J.P.

1987-01-01

High-T/sub c/ superconductivity is investigated by a microwave-cavity perturbation technique in the compound La/sub 1.8/Sr/sub 0.2/CuO 4 . Both the microwave loss and frequency shift show a rapid decrease at 39 K, the onset of the superconducting transition. A significant microwave absorption is also observed well below the transition. The data are used to determine the sample resistivity in the normal state and characterize the superconducting transition in an applied magnetic field

Superconductivity and ceramic superconductors II; Proceedings of the Symposium, Orlando, FL, Nov. 12-15, 1990. Ceramic transactions. Vol. 18

International Nuclear Information System (INIS)

Nair, K.M.; Balachandran, U.; Chiang, Y.-M.; Bhalla, A.S.

1991-01-01

The present symposium on superconductivity and ceramic superconductors discusses fundamentals and general principles, powder processing and properties, fabrication and properties, and device reliability and applications. Attention is given to phase formation in the Tl-Ca-Ba-Cu-O system, comparative defect studies in La2CuO4 and La2NiO4, solid solution and defect behavior in high Tc oxides, oxygen ion transport and disorder in cuprates, and Sr-free Bi-Ln-Ca-Cu-O superconductors. Topics addressed include the preparation of superconductor Y-Ba-Cu-O powder by single-step calcining in air, low-temperature synthesis of YBa2Cu3O(7-x), synthesis of high-phase purity ceramic oxide superconductors by the xerogel method, and the preparation and characterization of the BYa2Cu4O8 superconductor. Also discussed are optical studies of humidity-based corrosion effects on thin film and bulk ceramic YBa2Cu3O(7-delta), thermomechanical processing of YBa2Cu3O(x)/Ag sheathed wires, and the expansion of high-Tc superconducting ceramics

Three-dimensionality of field-induced magnetism in a high-temperature superconductor

DEFF Research Database (Denmark)

Lake, B.; Lefmann, K.; Christensen, N.B.

2005-01-01

Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO(2) building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO(2) layers, the antiferromagnetism of the parent...

Evidence for a common high-temperature superconducting effect in La/sub 1.85/Sr/sub 0.15/CuO4 and YBa2Cu3O7

International Nuclear Information System (INIS)

Jean, Y.C.; Kyle, J.; Nakanishi, H.

1988-01-01

We report the positron-annihilation lifetime and Doppler-broadening energy spectra in La/sub 1.85/Sr/sub 0.15/CuO 4 superconductors for 10 4 and YBa 2 Cu 3 O 7 are similar and suggest that this is a consequence of a common physics involving the delicate balance between localized and itinerant-electron behavior

Flux motion and dissipation in high-temperature superconductors

International Nuclear Information System (INIS)

Gray, K.E.; Kim, D.H.

1991-08-01

The effects on flux motion and dissipation of interlayer coupling of the Cu-O planes along the c-axis are considered for the high- temperature superconductors (HTS). It is argued that for the highly-anisotropic HTS, the weak interlayer coupling plays a dominant role that can be described by incoherent Josephson tunneling between superconducting Cu-O bi- or tri-layers. In YBa 2 Cu 3 O 7 , the layers are strongly coupled, presumably because the conducting Cu-O chains short circuit the Josephson tunneling, so that these effects are weak or missing

Synthesis, structural characterization and fluctuation conductivity of HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}-}SrTiO{sub 3} composites

Energy Technology Data Exchange (ETDEWEB)

Uribe Laverde, M.A., E-mail: mauribel@bt.unal.edu.c [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia); Landinez Tellez, D.A.; Roa-Rojas, J. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia)

2010-12-15

Single-phase polycrystalline samples of HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductor and SrTiO{sub 3} isolator were produced by means of the solid state reaction technique. After structural characterization of both materials, superconductor-isolator composites were produced with nominal isolator volume percentages between 0% and 10%. Resistivity measurements for the composites and the HoBa{sub 2}Cu{sub 3}O{sub 7-{delta}} sample with different currents evidenced a superconducting transition with critical temperature T{sub C} = 92 K, with wider transitions with increasing either isolator content or measurement current. Fluctuation conductivity analyses were carried out to obtain the exponents characterizing the conductivity divergence. Above T{sub C}, apart from the typical Gaussian and critical fluctuations an atypical regime with critical exponent about 0.14 is observed as a precursor of the transition. Below T{sub C}, it is observed that the coherence transition characteristic exponent increases rapidly with increasing isolator percentage in the composites and does not show important changes when modifying the current in the pure superconductor sample.

Epitaxial heterojunctions of oxide semiconductors and metals on high temperature superconductors

Science.gov (United States)

Vasquez, Richard P. (Inventor); Hunt, Brian D. (Inventor); Foote, Marc C. (Inventor)

1994-01-01

Epitaxial heterojunctions formed between high temperature superconductors and metallic or semiconducting oxide barrier layers are provided. Metallic perovskites such as LaTiO3, CaVO3, and SrVO3 are grown on electron-type high temperature superconductors such as Nd(1.85)Ce(0.15)CuO(4-x). Alternatively, transition metal bronzes of the form A(x)MO(3) are epitaxially grown on electron-type high temperature superconductors. Also, semiconducting oxides of perovskite-related crystal structures such as WO3 are grown on either hole-type or electron-type high temperature superconductors.

Device-quality tunnel junctions on the high Tc superconductor HgBa2CuO4+δ

International Nuclear Information System (INIS)

Zasadzinski, J.; Chen, J.; Romano, P.; Gray, K.E.; Wagner, J.L.; Hinks, D.G.

1995-01-01

SIN and SIS tunnel junction devices (e.g. photon detectors, logic elements) require quasiparticle characteristics that exhibit sharp current onsets at the gap voltage and very low sub-gap conductances. Progress is reported on the development of such junctions on High Tc cuprates using mechanical point contacts. In general, these contacts display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. Most cuprates display a sub-gap conductance which monotonically increases with voltage about the minimum value at zero bias. However, tunneling data of unusually high quality have been obtained for the recently discovered Hg-based cuprate, HgBa 2 CuO 4 (T c =96K). SIS' tunneling data using a Nb tip are presented which exhibit very low and flat sub-gap conductances and sharp conductance peaks as expected from a BCS density of states. These results are slightly improved over earlier published results with SIN junctions. Use of the experimental data to simulate the performance of a quasiparticle mixer demonstrates that noise temperatures approaching the quantum limit are possible for SIS and SIN mixers in the range 1-5 THz

Magnetic properties of the high-Tsub(c) superconductors RBa2Cu3Osub(9-delta) (R=Gd, Dy, Er)

International Nuclear Information System (INIS)

Groot, P.A.J. de; Rainford, B.D.; McK-Paul, D.; Balakrishnan, G.; Lanchester, P.C.; Weller, M.T.; Grasmeder, J.

1987-01-01

Magnetic properties of RBa 2 Cu 3 Osub(9-delta) with R = Y, Gd, Dy, Er have been measured for 4.2 K < T < 300 K and magnetic fields up to 7 T. They exhibit a superconductive transition around 91 K, above which temperature the magnetisation can be described by a Curie-Weiss law. The magnetic and superconductive properties develop independently below the phase transition. Magnetic hysteresis is prominent at low temperatures (T < or approx. 25 K) and varies for different samples. Estimates for critical densities are given. (author)

Flux motion and dissipation in high-temperature superconductors

International Nuclear Information System (INIS)

Gray, K.E.; Kim, D.H.

1991-01-01

The effects on flux motion and dissipation of interlayer coupling of the Cu-O planes along the c-axis are considered for the high-temperature superconductors (HTS). It is argued that for the highly-anisotropic HTS, the weak interlayer coupling plays a dominant role that can be described by incoherent Josephson tunneling between superconducting Cu-O bi- or tri-layers. In YBa 2 Cu 3 O 7 , the layers are strongly coupled, presumably because the conducting Cu-O chains short circuit the Josephson tunneling, so that these effects are weak or missing. Recently, the effects of anisotropy and fluctuations on critical current densities, J c (T,H) and the field-induced broadening of resistivity transitions, ρ(T,H), have been studied in high-temperature superconductors (HTS). Although the broadening looks similar for the applied field, H, oriented either parallel to the superconducting Cu-O layers (H parallel ab) or parallel to the c-axis (H parallel c), its width and the detailed shape of ρ(T,H) are different. The explanations given in this paper for the highly anisotropic HTS differ in detail for the two cases, but have a crucial feature in common: they result from fluctuations affecting the Josephson coupling across the interlayer junctions

Zinc substitution effects on the superconducting properties of Nd1.85Ce0.15CuO4-δ

International Nuclear Information System (INIS)

Garcia-Vazquez, V.; Mazumdar, S.; Falco, C.M.; Barlingay, C.; Risbud, S.H.

1990-01-01

With the discovery of the electron superconductors, a new dimension was added to research in the field of high-temperature superconductivity. Studies of these materials should help elucidate the mechanism responsible for high-temperature superconductivity, as well as improve strategies for finding new superconductors. In this paper, we discuss the superconducting structural properties of Nd 1.85 Ce 0.15 (Cu 1-y Zn y )O 4 as a function of the Zn concentration y. Detailed comparisons with previous results of similar substitution studies in the single-CuO 2 -layer hole superconductor La 1.85 Sr 0.15 CuO 4 also are made. We have found that the non-magnetic element Zn has a detrimental effect on the T'-phase electron superconductor, and that this effect is as strong as in the T-phase hole superconductor. Theoretical implications and the question of electron-hole symmetry are also discussed

Phenomenological theory of the normal and superconductive states of Cu-O and Bi-O metals

International Nuclear Information System (INIS)

Varma, C.M.

1991-01-01

The universal normal state anomalies in the CuO metals follow from a marginal Fermi liquid hypothesis: there exists a contribution to the polarizability over most of momentum space proportional to omega/T for omega/T much less than 1 and constant thereafter up to a cutoff omega(sub c). Using the same excitation spectrum, the properties of the superconductive state were calculated. The right order of T(sub c) can be obtained, the zero temperature gap, 2 delta (0)/T(sub c) and the nuclear relaxation rate near T(sub c). The possible microscopic physics leading to the marginal Fermi liquid hypothesis is discussed

High-Tc superconductors under very high pressure

International Nuclear Information System (INIS)

Wijngaarden, R.J.; Scholtz, J.J.; Eenige, E.N. van; Griessen, R.

1991-01-01

High pressure has played a crucial role in the short history of high T c superconductors. Soon after the discovery of superconductivity by Bednorz and Muller in La-Ba-Cu-O, Chu et al. showed that the critical temperature T c could be significantly increased by pressure. This observation led to the discovery of YBa 2 Cu 3 O 7 by Wu et al. with a T c above 90 K. Incidentally, this high T c is probably also due to the fact that YBa 2 Cu 3 O 7 has two CuO 2 layers per unit cell instead of a single one in La-Ba-Cu-O. The authors discuss the high pressure dependence of the oxide superconductors, particularly at pressures above 10 GPa, and the nonmonotonic dependence of transition temperature on pressure

La2CuO4+δ: Synthesis under high oxygen pressure and study of phase relations and energetics

International Nuclear Information System (INIS)

Rapp, R.P.; Mehta, A.; DiCarlo, J.; Navrotsky, A.

1994-01-01

High oxygen pressures have been achieved in a piston-cylinder apparatus using a double capsule assembly consisting of a sealed outer Au capsule, containing an oxygen source (KMnO 4 ), and an inner, open Pt capsule containing the sample. Using this technique, La 2 CuO 4 was annealed at 800 degree C, 5--25 kbar for 2--4 h. Transposed temperature drop calorimetry at 704 degree C was used to determine the enthalpy of oxidation, and weight loss measurements characterized the oxygen nonstoichiometry, δ, in La 2 CuO 4+δ , in the high-pressure, oxygen annealed samples. For samples analyzed at room temperature, x-ray diffraction measurements show that beyond δ∼0.10--0.13, additional oxygen is accommodated in a perovskite-like LaCuO 3-α phase. An analysis of the thermochemical measurements indicates that the nature of holes in La 2 CuO 4+δ could change in the range of δ∼0.03--0.06. 16,17 It is further suggested that the observed change in the thermochemical behavior in the range of δ∼0.01--0.06 could be the driving influence behind the spinodal decomposition of La 2 CuO 4+δ at low temperatures (Dabrowski et al. 10 )

Signature of electron-phonon interaction in high temperature superconductors

Directory of Open Access Journals (Sweden)

Vinod Ashokan

2011-09-01

Full Text Available The theory of thermal conductivity of high temperature superconductors (HTS based on electron and phonon line width (life times formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high Tc superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La1.8Sr0.2CuO4 in the temperature range 0 − 200K. The theory is equally and successfully applicable to all other high Tc superconductors.

Development of high temperature superconductors having high critical current density

Energy Technology Data Exchange (ETDEWEB)

Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H

2000-08-01

Fabrication of high T{sub c} superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm{sup 2} and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation.

Glassy spin freezing and NMR wipeout effect in the high-Tc superconductor La1.90Sr0.10CuO4: Critical discussion of the role of stripes

Science.gov (United States)

Julien, M.-H.; Campana, A.; Rigamonti, A.; Carretta, P.; Borsa, F.; Kuhns, P.; Reyes, A. P.; Moulton, W. G.; Horvatić, M.; Berthier, C.; Vietkin, A.; Revcolevschi, A.

2001-04-01

We report on 139La and 63Cu NMR/NQR measurements in the high-Tc superconductor La1.90Sr0.10CuO4, with Tc=26.5 K. Spin fluctuations probed by 139La spin-lattice relaxation (T1) continuously slow down on cooling through Tc. We argue that spin freezing and superconductivity are bulk effects in this sample. Thus both phenomena have to coexist microscopically. The distribution of 139La T1 values at low temperature reveals a wide spread of spin fluctuation frequencies in CuO2 planes. A simple estimate shows that 63Cu nuclei at sites where electronic fluctuations are the slowest are not observable (wipeout effect) because relaxation times are too short. This means that the 63Cu NQR wipeout, observed in this sample, can be explained primarily by slow magnetic, rather than charge, fluctuations. The magnetic origin of the wipeout is still compatible with a connection between wipeout and charge order [as proposed by Hunt et al., Phys. Rev. Lett. 82, 4300 (1999)], but this connection is indirect. On the other hand, since the wipeout fraction is not an intensive quantity it cannot define a proper order parameter and cannot be used by itself as a criterion for the existence of a stripe phase.

Nonlinear resistivity in a d-wave superconductor YBa{sub 2}Cu{sub 4}O{sub 8} of sub-micron scale grains

Energy Technology Data Exchange (ETDEWEB)

Deguchi, H; Shoho, T; Kato, Y; Ashida, T; Mito, M; Takagi, S [Faculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550 (Japan); Hagiwara, M [Faculty of Engineering and Design, Kyoto Institute of Technology, Kyoto 606-8585 (Japan); Koyama, K, E-mail: deguchi@tobata.isc.kyutech.ac.jp [Faculty of Integrated Arts and Science, The University of Tokushima 770-8502 (Japan)

2011-07-20

The d-wave ceramic YBa{sub 2}Cu{sub 4}O{sub 8} superconductor composed of sub-micron size grains is considered as random Josephson-coupled network of 0 and {pi} junctions and shows successive phase transitions. The upper transition occurs inside each grain at T{sub c1} = 82 K and the lower transition occurs among the grains at T{sub c2} = 66 K. We measured the temperature dependence of the current-voltage characteristics of the ceramic YBa{sub 2}Cu{sub 4}O{sub 8} and derived the linear and nonlinear resistivity. The nonlinear resistivity {rho}{sub 2} and {rho}{sub 4} have finite values between T{sub c1} and T{sub c2} and have the peak at the same temperature T{sub p} = 70 K above T{sub c2}. The result agrees with the theoretical one obtained by Li and DomInguez. They interpreted T{sub p} as the crossover temperature from the normal state phase to a chiral paramagnetic one.

Low energy excitations in superconducting La1.86Sr0.14CuO4

DEFF Research Database (Denmark)

Mason, T.E.; Aeppli, G.; Hayden, S.M.

1993-01-01

We present magnetic neutron scattering and specific heat data on the high-T(c) superconductor La1.86Sr0.14CuO4. Even when the samples are superconducting and the magnetic response, chi'', is suppressed, there are excitations with energies well below 3.5k(B)T(c). The wave-vector dependence of chi...

Probe high-Tc Superconductors by neutron scattering

International Nuclear Information System (INIS)

Fauque, B.

2007-10-01

This research thesis explores two aspects of the phase diagram of high critical temperature superconductors: the evolution of AF correlations and the nature of the pseudo-gap phase. The author presents the problematic associated with these particular semiconductors, describes the neutron diffusion probe used in this study, and presents the three families of semiconductors investigated during this research: Bi 2 Sr 2 CaCu 2 O 8+x , YBa 2 Cu 3 O 6+x and La 2-x Sr x CuO 4 . He reports the results of the investigation of the spin dynamics in the Bi 2 Sr 2 CaCu 2 O 8+x . He reports a detailed investigation of the magnetic cross section associated with different types of non conventional magnetic orders proposed as candidates for the pseudo-gap phase. He reports and comments the results obtained for the pseudo-gap phase for the YBa 2 Cu 3 O 6+x and La 2-x Sr x CuO 4 families. Finally, the author discusses the consequences of the obtained results for the description of the diagram phase of high critical temperature semiconductors

Lattice instabilities and structural phase transformations in La2CuO4 superconductors and insulators

International Nuclear Information System (INIS)

Axe, J.D.

1991-01-01

Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La 2 CuO 4 and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models

Oxygen doping of the high T/sub c/ superconducting perovskites

International Nuclear Information System (INIS)

Tarascon, J.M.; McKinnon, W.R.; Greene, L.H.; Hull, G.W.; Bagley, B.G.; Vogel, E.M.; Le Page, Y.

1987-01-01

Oxygen defect perovskites are studied because of their ability to reversibly intercalate oxygen atoms. Our previous studies of the La/sub 2-y/Sr/sub y/CuO/sub 4-x/ system shows that T/sub c/ is dramatically affected by subtle changes in oxygen content. However since this study did not achieve large values of x, a systematic study was not undertaken. The authors have found by thermogravimetric analysis (TGA) that a wide range of oxygen non-stoichiometry in the 90K superconductor YBa/sub 2/Cu/sub 3/O/sub 7-x/ is obtainable. This study of the effect of oxygen doping on the transport properties of the 40K material, and a systematic analysis of this over a broader range in the 90K superconductor is presented

Electron paramagnetic resonance and AC susceptibility studies of Mn and Gd doped 1:2:3 superconductors

International Nuclear Information System (INIS)

La Robina, M.A.

1997-01-01

For many years superconductivity was considered to be a low temperature phenomenon occurring below ∼ 25K. All this changed in April 1986 when J. G. Bednorz and K. A. Muller showed that the oxide La 2-x Ba x CuO 4 becomes a superconductor at ∼ 30K. Later in December 1986 the oxides La 2-x Sr x CuO 4 and La 2-x Ba x CuO 4 synthesised under high pressure, were shown to superconduct at ∼ 40K and ∼ 50K, respectively. Finally in February 1987, Chu synthesised the classic superconductor YBa 2 Cu 3 O 6.8 , the so-called 1:2:3 material, which has a critical temperature circa 92K. In this thesis, electron paramagnetic resonance (EPR) and susceptibility measurements are reported on various superconductors. In 1987 Bowden et al., showed that pure phase 1:2:3 samples are characterised by an absence of Cu EPR signals. This contrasts sharply with the Green phase material, Y 2 Ba 1 Cu 1 O 5 , which shows a very large EPR signal with a g eff of 2.08. In an attempt to induce EPR signals, Mn doped 1:2:3 samples have been synthesised and characterised with EPR , AC susceptibility, XRD and SEM measurements. It is shown that Mn EPR signals are not evident in the Mn doped samples with a g eff of 2.09. Also, below T c the EPR signals of the lightly doped Mn samples vanish. It is argued that this is due to fluxoids motion within the superconductor, which gives rise to very large non-reproducible signals. It is suggested that the signals originate from Cu, impurity contaminants and multiple phases produced when the 1:2:3 superconductor is doped with Manganese (author)

High pressure study of high temperatures superconductors: Material base, universal Tc-behavior, and charge transfer

International Nuclear Information System (INIS)

Chu, C.W.; Hor, P.H.; Lin, J.G.; Xiong, Q.; Huang, Z.J.; Meng, R.L.; Xue, Y.Y.; Jean, Y.C.

1991-01-01

The superconducting transition temperature (T c ) has been measured in YBa 2 Cu 3 O 6.7 , YBa 2 Cu 3 O 7 , Y 2 Ba 4 Cu 7 O 15 , YBa 2 Cu 4 O 8 , Tl 2 Ba 2 Ca n-1 Cu n O n+4-δ , La 2-x Sr x CuO 4 , and La 2-x Ba x CuO 4 under high pressures. The pressure effect on the positron lifetime (τ) has also been determined in the first four compounds. Based on these and other high pressure data, the authors suggest that (1) all known cuprate high temperature superconductors (HTS's) may be no more than mere modifications of either 214-T, 214-T', 123, or a combination of 214-T' and 123, (2) a nonmonotonic T c -behavior may govern the T c -variation of all hole cuprate HTS's and (3) pressure can induce charge transfer leading to a T c -change. The implications of these suggestions will also be discussed

Nonequilibrium theory of dirty, current-carrying superconductors: Phase-slip oscillators in narrow filaments near T/sub c/

International Nuclear Information System (INIS)

Watts-Tobin, R.J.; Kraehenbuehl, Y.; Kramer, L.

1981-01-01

General equations for the dynamic behavior of dirty superconductors in the Ginzburg--Landau regime Vertical BarT/sub c/-TVertical Bar<< T/sub c/ are derived from microscopic theory. In the immediate vicinity of T/sub c/ a local equilibrium approximation leads to a simple generalized time-dependent Ginzburg--Landau equation. The oscillatory phase-slip solutions presented previously are discussed in greater detail

Copper based superconductors by the combination of blocking and mediating layers

International Nuclear Information System (INIS)

Shimizu, K.; Nobumasa, H.; Kawai, T.

1992-01-01

Copper based high temperature superconductors are composed of Cu-O 2 sheets in combination with thin atomic mediating layers and thick blocking layers which mediate and intercept interactions between Cu-O 2 sheets, respectively. New possible superconductors can be designed by the stacking of the Cu-O 2 sheets along with the periodic insertion of the mediating layers and different kinds of blocking layers. (orig.)

Room temperature chemically oxidized La2CuO4+y: Phase separation induced by thermal treatment

DEFF Research Database (Denmark)

Rial,C.; Moran, E.; Alario-Franco, M.A.

1997-01-01

The structure of roam temperature chemically oxidized La2CuO4+y [y = 0.103(4)] has been refined from powder neutron diffraction data using the space group Bmab. The modifications induced in the CuO2 and the LaO planes by the insertion of oxygen are consistent with the high T-c measured for this m......The structure of roam temperature chemically oxidized La2CuO4+y [y = 0.103(4)] has been refined from powder neutron diffraction data using the space group Bmab. The modifications induced in the CuO2 and the LaO planes by the insertion of oxygen are consistent with the high T-c measured...... a short treatment at 433 K, La2CuO4.103(4) undergoes a phase separation into two phases: phase 1, with estimated y(1) = 0.086(4) and T-cl = 30 K, and phase 2, with estimated y(2) = 0.12(1) and T-c2 = 17 K. By increasing the annealing times, phase 2 transforms to phase I and finally disappears. Therefore...

Dopant structural distortions in high-temperature superconductors: an active or a passive role?

International Nuclear Information System (INIS)

Haskel, D.; Stern, E.A.; Dogan, F.; Moodenbaugh, A.R.

2001-01-01

The parent compounds of high-temperature superconductors, such as YBa 2 Cu 3 O 6 and La 2 CuO 4 , are strongly interacting electron systems, rendering them insulators with Mott-Hubbard gaps of a few electron volts. Charge carriers (holes) are introduced by chemical doping, causing an insulator-metal (IM) transition and, at low temperatures, superconductivity. The role of dopants is widely seen as limited to the introduction of holes into the CuO 2 planes (i.e. occupying electronic states derived from Cu 3d x2-y2 and O 2p x,y atomic orbitals). Most theories of high-T c superconductivity deal with pairing interactions between these planar holes. Local distortions around dopants are poorly understood, because of the experimental difficulty in obtaining such information, particularly at low doping. This has resulted in the neglect, in most theories, of the effect of such distortions on the chemical and electronic structure of high-T c superconductors. Angular-resolved X-ray absorption fine structure (XAFS) spectroscopy on oriented samples is an ideal technique to elucidate the dopant distortions. Element specificity, together with a large orientation dependence of the XAFS signal in these layered structures, allows the local structure around dopants to be resolved. Results are presented here on (Sr, Ba) and Ni dopants, which substitute at the La and Cu sites, respectively, of insulating La 2 CuO 4 . The relevance of the measured local distortions for a complete understanding of the normal and superconducting properties of cuprates is discussed. (au)

Electronic structure and electron-phonon coupling in layered copper oxide superconductors

International Nuclear Information System (INIS)

Pickett, W.E.; Cohen, R.E.; Krakauer, H.

1991-01-01

Experimental data on the layered Cu-O superconductors seem more and more to reflect normal Fermi-liquid behavior and substantial correspondence with band structure predictions. Recent self-consistent, microscopic band theoretic calculations of the electronic structure, lattice instabilities, phonon frequencies, and electron-phonon coupling characteristics and strength for La 2 CuO 4 and YBa 2 Cu 3 O 7 are reviewed. A dominant feature of the coupling is a novel Madelung-like contribution which would be screened out in high density of states superconductors but survives in cuprates because of weak screening. Local density functional theory correctly predicts the instability of (La, Ba) 2 CuO 4 to both the low-temperature orthorhombic phase (below room temperature) and the lower-temperature tetragonal phase (below 50 K). (orig.)

Mercury nonstoichiometry of the Hg1-xBa2CuO4+δ superconductor and the P(Hg)-P(O2)-T phase diagram of the Hg-Ba-Cu-O system

International Nuclear Information System (INIS)

Alyoshin, V.A.; Mikhailova, D.A.; Rudnyi, E.B.; Antipov, E.V.

2002-01-01

The P(Hg)-P(O 2 )-T phase diagram of the Hg-Ba-Cu-O system for the Ba:Cu=2:1 ratio was experimentally studied and followed by means of the thermodynamic modeling. It was shown that the Hg 1-x Ba 2 CuO 4+δ (Hg-1201) superconductor possesses a significant range of Hg-nonstoichiometry and exists in a certain P(Hg), P(O 2 ) and T range. Mercury nonstoichiometry of Hg-1201 was investigated in the 923≤T≤1095 K; 2.0≤P(Hg)≤8.4 atm; 0.09≤P(O 2 )≤0.86 atm ranges. It was found that the mercury content varies in the range of 0.80-0.94 under these conditions. The Gibbs energy of the Hg-1201 phase was estimated as a function of temperature and mercury concentration. The obtained results allow optimizing the synthesis conditions of Hg-1201 with a given Hg-content including preparation of the Hg-stoichiometric phase

Coherent diffusive transport mediated by Andreev reflections at V=Delta/e in a mesoscopic superconductor/semiconductor/superconductor junction

DEFF Research Database (Denmark)

Kutchinsky, Jonatan; Taboryski, Rafael Jozef; Kuhn, Oliver

1997-01-01

We present experiments revealing a singularity in the coherent current across a superconductor/semiconductor/superconductor (SSmS) junction at the bias voltage corresponding to the superconducting energy gap V=Delta/e. The SSmS structure consists of highly doped GaAs with superconducting electrodes...

Hybrid crystals of cuprates and iron-based superconductors

Science.gov (United States)

Xia, Dai; Cong-Cong, Le; Xian-Xin, Wu; Jiang-Ping, Hu

2016-07-01

We propose two possible new compounds, Ba2CuO2Fe2As2 and K2CuO2Fe2Se2, which hybridize the building blocks of two high temperature superconductors, cuprates and iron-based superconductors. These compounds consist of square CuO2 layers and antifluorite-type Fe2 X 2 (X = As, Se) layers separated by Ba/K. The calculations of binding energies and phonon spectra indicate that they are dynamically stable, which ensures that they may be experimentally synthesized. The Fermi surfaces and electronic structures of the two compounds inherit the characteristics of both cuprates and iron-based superconductors. These compounds can be superconductors with intriguing physical properties to help to determine the pairing mechanisms of high T c superconductivity. Project supported by the National Basic Research Program of China (Grant No. 2015CB921300), the National Natural Science Foundation of China (Grant Nos. 1190020 and 11334012), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07000000).

Electronic-structure Fermi-liquid theory of high-Tc superconductors: Comparison of predictions with experiments

International Nuclear Information System (INIS)

Yu, Jaejun; Freeman, A.J.

1991-01-01

Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations

Effect of exciton pairing on the stationary Josephson current in superconductor-semimetal-superconductor junctions

International Nuclear Information System (INIS)

Itskovich, I.F.; Shekhter, R.I.

1983-01-01

The effect of exciton pairing of charge carriers in a semimetal on the stationary Josephson current in superconductor-semimetal-superconductor junctions is considered. It is shown that the phase transition of the semimetal interlayer into an exciton dielectric state for T/sub γ/< T/sub c/ (T/sub γ/, T/sub c/ are the superconducting and exciton transition temperatures, respectively) is accompanied by a kink on the critical current j/sub c/ versus temperature curve at the point T = T/sub γ/. A sharp nonmonotonic temperature dependence of the reduced current j/sub c//j/sub c/0 (j/sub c/0 is the critical current at T/sub γ/ = 0) is also possible in the range T< T/sub γ/. At low temperatures T<< v/sub 1,2//d<< T/sub γ/ (v/sub 1,2/ are the Fermi velocities of the carriers in the semimetal, d is the thickness of the interlayer) the critical current of the superconductor-semimetal-superconductor junction is exponentially smaller than the current in the absence of exciton pairing

NQR study in superconducting La2CuO4+δ

International Nuclear Information System (INIS)

Ueda, K.; Sugata, T.; Kohori, Y.; Oda, Y.; Kohara, T.

1992-01-01

Cu NQR signals were observed around 33.1 and 36.0 MHz together with the antiferromagnetic Cu NMR signals in the superconducting La 2 CuO 4+ δ obtained by annealing in high pressure oxygen gas. The NQR intensity increases with increasing oxygen contents. The nuclear spin-lattice relaxation time, T 1 , of Cu NQR indicates that the paramagnetic phase is in the superconducting state at low temperatures. These results show that the NQR and NMR signals were coming from the Cu sites in the superconducting phase and the antiferromagnetic phase, respectively. No appreciable differences were observed in the Cu NQR spectrum and the relaxation time between the superconducting La 2 CuO 4 + δ samples annealed under the oxygen pressure of 400 ≅ 1200 bar. (orig.)

Magnetic properties of the high-Tsub(c) superconductors RBa/sub 2/Cu/sub 3/Osub(9-delta) (R=Y) (Gd, Dy, Er)

Energy Technology Data Exchange (ETDEWEB)

Groot, P.A.J. de; Rainford, B.D.; McK-Paul, D.; Balakrishnan, G.; Lanchester, P.C.; Weller, M.T.; Grasmeder, J.

1987-08-01

Magnetic properties of RBa/sub 2/Cu/sub 3/Osub(9-delta) with R = Y, Gd, Dy, Er have been measured for 4.2 K < T < 300 K and magnetic fields up to 7 T. They exhibit a superconductive transition around 91 K, above which temperature the magnetisation can be described by a Curie-Weiss law. The magnetic and superconductive properties develop independently below the phase transition. Magnetic hysteresis is prominent at low temperatures (T

Creation of the best performance high-$T_{c}$ superconductor based on Cu-1234

CERN Document Server

Ihara, H; Iyo, A; Kito, H; Terada, N; Tokumoto, M; Ishida, K; Sekita, Y; Yamamoto, H; Hayashi, H; Khan, N A; Sundaresan, A; Nie, J; Harashima, E; Ishiura, Y; Tateai, F; Kawamura, M

1999-01-01

The purpose of this project is to create the best performance superconductor on the basis of our original Cu-1234 (CuBa/sub 2/Ca /sub 3/Cu/sub 4/O/sub 12-y/) superconductor. Its best performance superconductor will be realized by the modification of superconducting wave function (MSWF) and application of new preparation techniques of thin films. The MSWF leads to the enhancement of coherence length along the c-axis and transformation from d-wave to (d+is)-wave, and then low superconducting anisotropy. The thin film techniques are APE (amorphous phase epitaxy) method and SAE (self assembling epitaxy) method by using a structure stabilizer such as Tl. The best superconductor with long coherence length, low anisotropy, high T/sub c/, high J/sub c/ and high H/sub irr/ will be realized for wire and Josephson junctions and microwave device application at 77 K. (16 refs).

Substitution effect of Sr2+ by Ca2+ on structure and superconducting properties of Bi2Sr1.6La0.4CuO6+δ (Bi-2201) ceramics

Science.gov (United States)

Boudjaoui, S.; Amira, A.; Mahamdioua, N.; Altintas, S.; varilci, A.; Terzioglu, C.

2018-02-01

In this work, the effect of Ca2+ iso-valence substitution for Sr2+ on properties of Bi2Sr1.6La0.4CuO6+δ superconductors is presented. Samples series with nominal composition of Bi2Sr1.6-xCaxLa0.4CuO6+δ (x= 0, 0.2, 0.4, 0.6 and 0.8) are prepared by a solid-state reaction method. When Ca content is increased, the X-ray diffraction technique shows that the cell parameters a and c decrease, while b one is almost constant. The scanning electron microscopy analysis reveals that the substitution has no significant effect on the porosity and the grain size of the samples. The physical properties of the samples are studied by the analysis of the magneto-resistivity curves measured under magnetic fields in the range 0-1 T. As Ca is added, the results show that the high temperature transition appears and is pushed up to 94.87 K for x=0.8. The substitution also improves the bulk onset critical transition temperature, the transition width, the residual resistivity, the activation energy of vortices and the irreversibility field. The best results are seen for x=0.4 of Ca content.

T/sub 4/ radioimmunoassay with ion-exchange resin separation

Energy Technology Data Exchange (ETDEWEB)

Michael, J D; Modha, K [Hoechst Pharmaceuticals Research Ltd., Milton Keynes (UK)

1977-05-28

An explanation is provided for the reports of falsely low values of serum-thyroxine (T/sub 4/) measured by radioimmunoassay (RIA), particularly in sera containing raised concentrations of thyroxine-binding globulin (TBG) (Burr, W.A., Evans, S.E., Hogan, T.C., 1977, Lancet, April 2, 757). A re-examination of the assay technique used in commercial RIA kits ('RIA-gnost T/sub 3/' and 'RIA-gnost T/sub 4/', Behring Diagnostics) showed that blocking of binding proteins by 8-anilino-1-naphthalene sulphonic acid (ANS) was incomplete in sera with raised TBG levels. Spectroscopic determination of the blocker concentration during the time the solution was in contact with the ion exchange resin showed that 98% of the ANS was removed from solution by 10 min contact with the resin, yet 60 min was required to absorb the free T/sub 4/. There was therefore ample time for unblocked TBG to recombine with free T/sub 4/ which was then misclassified as antibody-bound T/sub 4/. The assay technique used in the kits was therefore modified. The less polar TBG blocking agent, ethylmercurithiosalicylate (merthiolate), replaced ANS and it was demonstrated that accurate T/sub 3/ and T/sub 4/ measurements in high TBG sera could be made by resin-separation RIA without resorting to prior denaturation or alcohol extraction.

Study of magnetic excitations in the high critical temperature La2-xSrxCuO4 superconductor with neutrons inelastic scattering

International Nuclear Information System (INIS)

Petit, S.

1997-01-01

In this work, we question the relevance of spin correlations in the problem of high-T c superconductivity. To characterize these correlations, we present a detailed inelastic neutron scattering study of the magnetic excitations spectrum, in the high T c La 2-x Sr x CuO 4 copper oxide superconductor, as a function of temperature and strontium content x. Our study demonstrates the existence of two distinct types of fluctuations. The first type corresponds to two-dimensional isotropic fluctuations peaked at incommensurate points around the antiferromagnetic wavevector. These fluctuations show a gap below T c . The second type of fluctuations corresponds to two-dimensional very low energy, typically 1 MeV, antiferromagnetic correlations. They arise at low temperatures, for T ≤T f ∼ 10 K ≤T c . Different scenarios are discussed, namely particle-hole excitation arising because of nesting properties of the Fermi surface, stripes, and localized carriers in the CuO 2 plane because of the La/Sr substitution disorder. Next, aiming to study the interrelation between magnetism and superconductivity, we present a theoretical perturbative treatment of the t-t'-J model. This model is believed to describe the physics of the CuO 2 plane. The considered quasiparticles describe the motion of a doped hole, followed by localized spins on the copper sites. For a given doping x, two phases can exist, containing either x or 1 + x of these quasiparticles. We show at in the second phase, the exchange interaction between localized spins, combined to the intrinsic anharmonicity of these quasiparticles leads to an attractive interaction between them. We study the stability and the symmetry of a superconducting phase based on this mechanism. (author)

Raman studies of lanthanum cuprate superconductors

International Nuclear Information System (INIS)

Weber, W.H.; Peters, C.R.; Logothetis, E.M.

1989-01-01

Raman-scattering studies of the high-T/sub c/ superconductor La/sub 2-//sub x/(Sr, Ba)/sub x/CuO 4 are briefly reviewed. A detailed analysis of the phonon-mode symmetries is given along with a discussion of the effects expected from the orthorhombic-to-tetragonal phase transition, which is known to occur in these materials. Survey spectra are given for powders, ceramics, and single crystals, and an oxide of Cu is identified as the primary impurity phase. Extensive spectra are given from oriented single crystals of La 2 CuO 4 and La/sub 1.85/Sr/sub 0.15/CuO 4 , and several mode assignments are made. Spectra for the high-temperature tetragonal phase and the low-temperature orthorhombic phase are given for each material. The soft phonon associated with the phase transition is seen in La 2 CuO 4 as is a broad peak arising from two-magnon scattering. Neither of these features is seen in the Sr-doped sample

Orbitals, correlation, valencies in high-Tc superconductors

International Nuclear Information System (INIS)

Khomskii, D.I.

1990-09-01

The survey is given of certain properties of high-Tc superconductors connected with the details of their electronic structure such as the kind of orbitals involved and the degree of correlation. Special attention is paid to the properties of cuprates at high doping level. The problem whether there exists a ''Mott transition'' at high electron or a hole concentration is discussed. We also discuss physical factors (d-p Coulomb interaction, orbital mixing) leading to the partial occupation of copper d x 2 -orbital. In particular we show that in localized picture (x 2 -y 2 ) and z 2 -levels in La 2-x Sr x CuO 4 may cross at x approx. 0.4 which may be responsible for a marked change of many properties at this doping. The possible role of x 2 -electrons in pairing is discussed in connection with some recent experiments. (author). 28 refs, 6 figs, 1 tab

Oxygen desorption from YBa2Cu3O(7-x) and Bi2CaSr2Cu2O(8 + delta) superconductors

Science.gov (United States)

Mesarwi, A.; Levenson, L. L.; Ignatiev, A.

1991-01-01

Oxygen desorption experiments from YBa2Cu3O(7-x) (YBCO) and Bi2CaSr2Cu2O(8 + delta) (BSCCO) superconductors were carried out using a quadrupole mass spectrometer for monitoring the desorbing species and X-ray photoemission spectroscopy for surface characterization. Molecular oxygen was found to desorb from both superconductors following photoirradiation with ultraviolet/optical radiation and subsequent heating at over 150 C. Both YBCO and BSCCO were found to have similar oxygen desorption rates and similar activation energies. The desorption data as well as the X-ray photoemission data indicate that the oxygen desorption is not intrinsic to the superconductors but rather due to molecular oxygen entrapped in the material.

Random phase approximations for the screening function in high Tc superconductors

International Nuclear Information System (INIS)

Lopez-Aguilar, F.; Costa-Quintana, J.; Sanchez, A.; Puig, T.; Aurell, M.T.; Martinez, L.M.; Munoz, J.S.

1990-01-01

This paper reports on the electronic transferences from the CuO 2 sheets toward the CuO 3 linear chain, which locate electrons in the orbitals p y /p z of O4/O1 and d z 2 -y 2 of Cu1, and holes in the orbitals d x 2 -y 2 - P z /p y of Cu2 - P2/O3. These holes states present large interatomic overlapping. In this paper, we determine the screening function within the random phase approximation applied to the high-T c superconductors. This screening function is vanishing for determined values of the frequency which correspond to renormalized plasmon frequencies. These frequencies depends on the band parameters and their knowledge is essential for determining the self energy. This self energy is deduced and it contain independent terms for each of the channels for the localization

Effect of rare-earth ion size on local electron structure in RBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (R = Tm, Dy, Gd, Eu, Nd and Y) superconductors: A positron study

Energy Technology Data Exchange (ETDEWEB)

Chen Zhenping [Department of Technology and Physics, Zhengzhou University of Light Industry, 5 Dongfeng Road, Zhengzhou, Henan 450002 (China)]. E-mail: czhping@zzuli.edu.cn; Zhang Jincang [Department of Physics, Shanghai University, Shanghai 200436 (China); Su Yuling [Department of Technology and Physics, Zhengzhou University of Light Industry, 5 Dongfeng Road, Zhengzhou, Henan 450002 (China); Xue Yuncai [Department of Technology and Physics, Zhengzhou University of Light Industry, 5 Dongfeng Road, Zhengzhou, Henan 450002 (China); Cao Shixun [Department of Physics, Shanghai University, Shanghai 200436 (China)

2006-02-15

The effects of rare-earth ionic size on the local electron structure, lattice parameters and superconductivity have been investigated by positron annihilation technique (PAT) and related experiments for RBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (R = Tm, Dy, Gd, Eu, Nd and Y) superconductors. The local electron density n {sub e} is evaluated as a function of the rare-earth radius. The results show that both the bulk-lifetime {tau} {sub B} and the defect lifetime {tau} {sub 2} increase with increasing rare-earth ionic radius, while the local electron density n {sub e} decrease with increasing rare-earth ionic radius. These results prove that the changes of n {sub e}, the degree of orthorhombic distortion and the coupling between the Cu-O chains and the CuO{sub 2} planes all have an effect on the superconductivity of RBa{sub 2}Cu{sub 3}O{sub 7-{delta}} systems.

Positron annihilation studies on high temperature superconductors

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.

1991-01-01

The results of positron annihilation measurements as a function of temperature, across Tc, in a variety of high temperature superconductors such as Y-Ba-Cu-O (Y1237), Y-Ba-Cu-O (Y1248), Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu-O, Ba-K-Bi-O and Nd-Ce-Cu-O are presented. It is shown that the variation of annihilation parameters in the superconducting state is correlated with the diposition of the positron density distribution with respect to the superconducting CuO planes. An increase in positron lifetime is observed below Tc when the positrons probe the CuO planes whereas a decrease in lifetime is observed when the positron density overlaps predominantly with the apical oxygen atom. With this correlation, the different temperature variation of annihilation parameters, seen in the various high temperature superconductors, is understood in terms of a local charge transfer from the planar oxygen atom to the apical oxygen atom. The significance of these results in the context of various theoretical models of high temperature superconductivity is discussed. In addition, the application of positron annihilation spectroscopy to the study of oxygen defects in the Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O and Nd-Ce-Cu-O is presented. (author). 53 refs., 17 figs., 2 tabs

μSR-investigation of high-Tc superconductors at the LNP JINR phasotron

International Nuclear Information System (INIS)

Bezhitadze, D.T.; Borovinskaya, I.P.; Burianek, J.

1989-01-01

High-T c superconductors La 2-x Sr x CuO 4 (x=0+0.25), Ho(Er)Ba 2 Cu 3 O 7-y and Bi-Sr-Ca-Cu-O (the main phase 2212 with a small admixture of the 2223-phase) were investigated in the zero and 100+400 Oe transverse external magnetic fields in the temperature interval 4.2+300 K. The magnetic ordering for the La 2-x Sr x CuO 4 samples with x=0.00 and x=0.01 occurs below T N ∝250 K and T N ∝170 K respectively. A considerable increase in the distribution width of the magnetic field on the muon with an increase in the Sr-content indicates an enhancement of the Cu 2+ magnetic moment deviation from the magnetic ordering axis. The results of the analysis of the μSR spectra indicate the formation of the spin glass state in the La 1.93 Sr 0.07 CuO 4 sample. In contrast to the behaviour of the HoBa 2 Cu 3 O 7-y ceramic the magnetic ordering of the Er-atoms in the ErBa 2 Cu 3 O 7-y sample is not observed in the conparable temperature interval. Our data has also allowed the magnetic field penetration depth λ perpendicular (0) to be determined: 3200±70 A for La 1.9 Sr 0.1 CuO 4 , 2420±60 A for La 1.85 Sr 0.15 CuO 4 , 2000±50 A for Bi-Sr-Ca-Cu-O (phase 2212), 1600±50 A for ErBa 2 Cu 3 O 7-y . 20 refs.; 8 figs

The vacancy order-disorder transition in Ba2YCu3Osub(7-delta) observed by means of electron diffraction and electron microscopy

International Nuclear Information System (INIS)

Tendeloo, G. Van; Amelinckx, S.; Zandbergen, H.W.

1987-01-01

It is shown by means of electron microscopy and electron diffraction that the ''structural'' vacancies in Ba 2 YCu 3 Osub(7-delta) undergo an order-disorder transformation accompanied by a change in symmetry from orthorhombic to tetragonal. A superstructure due to the ordering of vacancies was found in certain crystal parts; it leads to doubling of the asub(0) parameter. It is shown that the ordering of the vacancies is important for the superconducting behaviour. In order to obtain a high Tsub(c) superconductor the final heat treatment is crucial. (author)

Charge redistribution and properties of high-temperature superconductors

International Nuclear Information System (INIS)

Khomskii, D.I.; Kusmartsev, F.V.

1992-01-01

We show that in high-T c superconductors (HTSC) with two groups of electrons (e.g., holes in CuO 2 planes and in a ''reservoir'') there should exist a charge redistribution with the temperature: the hole concentration N h in ''active'' superconducting CuO 2 planes increases below T c . This effect may explain structural changes such as the shift of the apical oxygen atom, anomalous thermal expansion, the shift of nuclear quadrupole resonance lines, the change of the positron lifetime, and the modification of the ion channeling below T c . Some other possible consequences of the charge redistribution (the modification of the temperature dependence of a gap Δ and of the ratio 2Δ 0 /T c , the phenomena at a contact of HTSC with normal metals and semiconductors) are discussed

HREM study of Bi-oxide based high Tc superconductors

International Nuclear Information System (INIS)

Hewat, E.A.

1988-01-01

A HREM study of the superstructure and structural defects in Bi 2-x Pb x Sr 2 CaCu 2 O 8 and Bi 2-x Pb x (SrCa) 2 CuO 6 (for x=0 and x=0.4) is presented. The superstructures are shown to involve waves of distortion along the b-axis. These waves are locked on to the lattice positions so that they have a local wave length of 4,5,6,7 or 8 times the basic unit cell. The superstructures are composed of roughly periodic combinations of these basic building blocks (waves). The lead doped superconductors show a less pronounced but more complicated superstructure along b where two distinct periodicities close to 4 and 7 times the basic unit cell predominate. In each of the compounds studied the superstructure, in the better ordered crystals, is shown to be commensurate with a unit cell between 5 and 23 times the basic unit cell. The superstructure in Bi 2-x Pb x Sr 2 CaCu 2 O 8 is orthorhombic where as the superstructure in Bi 2-x Pb x (SrCa) 2 CuO 6 is monoclinic. All these superconductors have a low ''twin'' density (ie density of 90 0 twist boundaries). They exhibit many dislocations and dislocation arrays associated with the weak bonding between BiO planes. They also form non-stoechiometric stacking faults with local changes in the c-axis spacing between layers

Oxygen diffusion in cuprate superconductors

International Nuclear Information System (INIS)

Routbort, J.L.; Rothman, S.J.

1995-01-01

Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. This article reviews studies of the diffusion of oxygen in La 2-x Sr x CuO 4 , YBa 2 Cu 3 O 7- δ, YBa 2 Cu 4 O 8 , and the Bi 2 Sr 2 Ca n-1 Cu n O 2+4 (n = 1, and 2) superconductors, and attempt to elucidate the atomic mechanisms responsible

Study of the glass formation of high temperature superconductors

Science.gov (United States)

Ethridge, Edwin C.; Kaukler, William F.; Rolin, Terry

1992-01-01

A number of compositions of ceramic oxide high T(sub c) superconductors were elevated for their glass formation ability by means of rapid thermal analysis during quenching, optical, and electron microscopy of the quenched samples, and with subsequent DSC measurements. Correlations between experimental measurements and the methodical composition changes identified the formulations of superconductors that can easily form glass. The superconducting material was first formed as a glass; then, with subsequent devitrification, it was formed into a bulk crystalline superconductor by a series of processing methods.

Macroscopic phase separation in high-temperature superconductors

Science.gov (United States)

Wen, Hai-Hu

2000-01-01

High-temperature superconductivity is recovered by introducing extra holes to the Cu-O planes, which initially are insulating with antiferromagnetism. In this paper I present data to show the macroscopic electronic phase separation that is caused by either mobile doping or electronic instability in the overdoped region. My results clearly demonstrate that the electronic inhomogeneity is probably a general feature of high-temperature superconductors. PMID:11027323

Observation of a hexatic vortex glass in flux lattices of the High-Tc superconductor Bi(2.1)Sr(1.9)Ca(0.9)Cu2O(8 + delta)

Science.gov (United States)

Murray, C. A.; Gammel, P. L.; Bishop, D. J.; Mitzi, D. B.; Kapitulnik, A.

1990-05-01

Hexatic order is observed in Abrikosov flux lattices in very clean crystals of the high-Tc superconductor Bi(2.1)Sr(1.9)Ca(0.9)Cu2O(8 + delta) by in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants, while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent eta6 = 0.06 + or - 0.01. These results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order, and that the low-temperature ordered phase of the flux lines in these systems might be a hexatic glass.

Positron annihilation study of the high-Tc (Bi, Pb)2Sr2Ca2Cu3Ox superconductor

International Nuclear Information System (INIS)

Lim, H.J.; Byrne, J.G.

1997-01-01

Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high-T c lead-doped Bi 2 Sr 2 Ca 2 Cu 3 O x (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters (S, W, and S/W) showed significant change through T c . This may result from having the highest positron density in the open BiO 2 double layers and no significant positron density in the superconducting CuO 2 layers where positrons, if mainly present, are known to be sensitive to the transition in other high-T c superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample (τ 1 ) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample (τ 2 ) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps. (orig.)

Spectroscopic study of the CuO chains in YBa2Cu3O7-x

International Nuclear Information System (INIS)

Edwards, H.; Derro, D.J.; Barr, A.L.; Markert, J.T.; de Lozanne, A.L.

1996-01-01

We interpret our previously published results obtained using a technique called current-imaging tunneling spectroscopy (CITS) to study the detailed electronic structure of the CuO chains in the high-temperature superconductor YBa 2 Cu 3 O 7-x near the Fermi level. Our CITS data comprise sequences of 32 simultaneously obtained images taken at bias voltages ranging from -78 to 72 mV. Cross sections of the CITS data, normalized-conductance analysis, and logarithmic-derivative analysis allow us to examine in detail the behavior of electronic modulations along the CuO chains and the energy gap in the CuO chains of YBa 2 Cu 3 O 7-x . This new analysis lends a strong foundation to our previous interpretation of the CITS data [H. L. Edwards et al., Phys. Rev. Lett. 75, 1387 (1995)]. copyright 1996 American Vacuum Society

Debye frequency and interplay of superconductivity and antiferromagnetism in high T{sub c} superconductors

Energy Technology Data Exchange (ETDEWEB)

Panigrahy, N N [Siddartha Nagar 2, Berhampur (India); Mahapatra, D [T.T. College, Ganjam (India); Panda, B N [DAV College, Koraput (India); Rout, G C [Govt. Science College, Ganjam (India)

2006-04-15

The interplay between superconductivity (SC) and antiferromagnetism (AFM) is studied in strongly correlated systems: R{sub 2-x}M{sub x}CuO{sub 4} (R = Nd, La, Pr. Gd; M = Sr, Ce) due to electron-phonon interaction, It is assumed that SC arises due to BCS pairing mechanism in presence of AFM in Cu lattices of Cu-O planes, Debye frequency {omega}{sub D} dependence of high temperature SC gap as well as staggered magnetic field at different temperatures are calculated analytically and solved self-consistently with respect to half-filled band situation for different model parameters (temperature parameter {theta} and hybridization parameter {nu}, {lambda}{sub 1} and {lambda}{sub 2} being the SC and AF coupling parameters, respectively). The SC gap and AFM gap are studied in their coexistence phase for different Debye frequencies. (author)

Bulk electronic structures of n-type superconductor Nd1.85Ce0.15CuO4 probed by high energy angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Tsunekawa, M.; Sekiyama, A.; Kasai, S.; Yamasaki, A.; Fujiwara, H.; Sing, M.; Shigemoto, A.; Imada, S.; Onose, Y.; Tokura, Y.; Muro, T.; Suga, S.

2005-01-01

We report on a high-energy angle-resolved photoemission (ARPES) study of the n-type high-T C cuprate, Nd 1.85 Ce 0.15 CuO 4 (NCCO). Our bulk sensitive results suggest a hole-like Fermi surface as seen by the so far reported low-energy ARPES studies. The soft X-ray Cu 2p core-level photoemission spectra show clear polar-angle dependence, suggesting the difference in electron states between the bulk and surface

Proximity-coupled CuO2 planes in high-Tc superconductors: evidence from pressure experiments up to 34 GPa on Y2Ba4Cu7O15.32

International Nuclear Information System (INIS)

Eenige, E.N. van; Griessen, R.; Heeck, K.; Schnack, H.G.; Wijngaarden, R.J.; Genoud, J.Y.; Graf, T.; Junod, A.; Muller, J.

1992-01-01

The Tc of superconducting Y 2 Ba 4 Cu 7 O 15.32 is measured up to a pressure of 33.7 GPa. After an initial increase from 95 K to 101.7 K a decrease down to 26.6 K is found, with a clear kink at 22 GPa. We demonstrate that Y 2 Ba 4 Cu 7 O 15.32 behaves as a multilayer of YBa 2 Cu 3 O 7 and YBa 2 Cu 4 O 8 building blocks coupled via the proximity effect. These data are not consistent with the idea that the coupling of two adjacent CuO 2 planes is necessary for superconductivity. (orig.)

Positron annihilation study in La2CuO4

International Nuclear Information System (INIS)

Kubo, Y.; Asano, S.

1992-01-01

The positron annihilation study for La 2 CuO 4 are performed using the full-potential linearized augmented-plane-wave(FLAPW) calculated electron and positron densities. The electron-positron momentum density(EPMD) is computed, and the well known Lock-Crisp-West(LCW) zone folding of the EPMD is produced. In the LCW analysis, small residual variations of order about 3 % are observed. The calculations show that the relative weights of the Fermi surface discontinuities are substantially altered due to the positron preferentially sampling the Cu-O plane region

Thermal conductivity in high critical temperature superconductors. Conductividad termica en los superconductores de alta temperatura critica

Energy Technology Data Exchange (ETDEWEB)

Castello, D J

1990-01-01

A measuring procedure to obtain the electrical resistivity, thermal conductivity and thermoelectric power of samples of low conductivity has been developed. The setup was designed to allow removal of the sample in clean fashion so that further heat treatments could be performed. The heat equation has been analyzed with time-dependent boundary conditions, with the purpose of developing a dynamic measuring method which avoids the long delays involved in reaching thermal equilibrium above 30K. The developed measuring method allows precise, reliable measurements in a continuous fashion for temperatures above 25K. The same setup is used in a stationary mode at low temperatures. {kappa}(T) has been measured in two ceramic samples of La{sub 2}CuO{sub 4}: the first semiconducting, the other superconducting (SC) as a consequence of an oxygen annealing. Both exhibit strong thermal resistivity due to defects, though lower in the SC, where two maxima are observed and are attributed to an AF ordering: T{sub N}' {approx equal} 40K and T{sub N}'' {approx equal} 240K. A third synthesized sample of CuO exhibits a typical behavior of an insulator, with T{sup 2}.6 at low temperatures, a maximum at 40K and a decrease in T{sup -1} at high temperatures. {kappa}(T) in a SC sample of La{sub 1}.85Sr{sub 1}.15CuO{sub 4} with T{sub c}=35.5K has also been measured. {kappa}(T) is lower than in the previous samples and thus a greater number of defects was inferred.

Electronic Structure of TlBa2CaCu2O(7-Delta)

Science.gov (United States)

Vasquez, R. P.; Novikov, D. L.; Freeman, A. J.; Siegal, M. P.

1997-01-01

The core levels of TlBa2CaCu2O(7-delta) (Tl-1212) epitaxial films have been measured with X-ray photoelectron spectroscopy (XPS). The valence electronic structure has been determined using the full-potential linear muffin-tin-orbital band-structure method and measured with XPS. The calculations show that a van Hove singularity (VHS) lies above the Fermi level (E(sub F)) for the stoichiometric compound (delta = 0.5), while for 50% oxygen vacancies in the Tl-O layer (delta = 0.5) E(sub F) is in close proximity to the VHS. Samples annealed in nitrogen (to reduce the hole overdoping by the removal of oxygen) exhibit higher core-level binding energies and a higher T(sub c), consistent with a shift of E(sub F) closer to the VHS. Comparisons are made to the core levels and valence bands of Tl2Ba2CaCu2O(8 + delta)(Tl-2212) and HgBa2CaCu2O)6 + delta) (Hg- 1212). The similarity of the Cu 2p(sub 3/2) spectra for Tl-1212 and Tl-2212 indicates that the number of Tl-O layers has little effect on the Cu-O bonding. However, the Tl-1212 and Hg-1212 Cu 2p(sub 3/2) signals exhibit differences which suggest that the replacement of T(sup 3+) with Hg(sup 2+) results in a decrease in the O 2p right arrow Cu 3d charge-transfer energy and differences in the probabilities of planar vs apical oxygen charge transfer and/or Zhang-Rice singlet-state formation. Differences between the Tl-1212 and the Tl-2212 and Hg-1212 measured valence bands are consistent with the calculated Cu 3d and (Tl,Hg) 6s/5d partial densities of states.

Revisiting 63Cu NMR evidence for charge order in superconducting La1.885Sr0.115CuO4

Science.gov (United States)

Imai, T.; Takahashi, S. K.; Arsenault, A.; Acton, A. W.; Lee, D.; He, W.; Lee, Y. S.; Fujita, M.

2017-12-01

The presence of charge and spin stripe order in the La2CuO4 -based family of superconductors continues to lead to new insight on the unusual ground-state properties of high-Tc cuprates. Soon after the discovery of charge stripe order at Tcharge≃65 K in Nd3 + co-doped La1.48Nd0.4Sr0.12CuO4 (Tc≃6 K) [Tranquada et al., Nature (London) 375, 561 (1995), 10.1038/375561a0], Hunt et al. demonstrated that La1.48Nd0.4Sr0.12CuO4 and superconducting La2 -xSrxCuO4 with x ˜1 /8 (Tc≃30 K) share nearly identical NMR anomalies near Tcharge of the former [Phys. Rev. Lett. 82, 4300 (1999), 10.1103/PhysRevLett.82.4300]. Their inevitable conclusion that La1.885Sr0.115CuO4 also undergoes charge order at a comparable temperature became controversial, because diffraction measurements at the time were unable to detect Bragg peaks associated with charge order. Recent advances in x-ray diffraction techniques finally led to definitive confirmations of the charge order Bragg peaks in La1.885Sr0.115CuO4 with an onset at as high as Tcharge≃80 K. Meanwhile, improved instrumental technology has enabled routine NMR measurements that were not feasible two decades ago. Motivated by these new developments, we revisit the charge order transition of a La1.885Sr0.115CuO4 single crystal based on 63Cu NMR techniques. We demonstrate that 63Cu NMR properties of the nuclear spin Iz=-1/2 to +1/2 central transition below Tcharge exhibit unprecedentedly strong dependence on the measurement time scale set by the separation time τ between the 90∘ and 180∘ radio-frequency pulses; a new kind of anomalous, very broad winglike 63Cu NMR signals gradually emerge below Tcharge only for extremely short τ ≲4 μ s , while the spectral weight INormal of the normal NMR signals is progressively wiped out. The NMR linewidth and relaxation rates depend strongly on τ below Tcharge, and their enhancement in the charge ordered state indicates that charge order turns on strong but inhomogeneous growth of Cu spin

Generation of the J/sub c/, H/sub c/, T/sub c/ surface for commercial superconductor using reduced-state parameters

International Nuclear Information System (INIS)

Green, M.A.

1988-04-01

This report presents a method for calculating the J/sub C/, H/sub C/, T/sub C/ surface for Type II Superconductors. The method requires that one knows T/sub C/ at zero current and field, H/sub c2/ at zero current and temperature, and J/sub c/ at at least one temperature and field. The theory presented in this report agrees with the measured data quite well over virtually the entire J/sub c/, H/sub c/, T/sub c/ surface given the value of J/sub c/ versus H at one or two temperatures. This report presents calculated and measured values of J/sub c/ versus T and B for niobium titanium, niobium zirconium, niobium tin, niobium titanium tin, niobium tantalum tin, vanadium zirconium hafnium, and vanadium gallium. Good agreement of theory with measured data was obtained for commercial niobium titanium and niobium tin. 76 refs., 26 figs., 6 tabs

Effects of magnetic field on the cuprate high-Tc superconductor La2-xSrxCuO4

DEFF Research Database (Denmark)

Lake, B.; Aeppli, G.; Christensen, N.B.

2004-01-01

This article discusses neutron scattering measurements on the cuprate, high transition temperature superconductor La2-xSrxCuO4 (LSCO) in an applied magnetic field. LSCO is a type-II superconductor and magnetic flux can penetrate the material via the formation of vorticies. Phase coherent...

Influence of doping on the electronic structure of (La, Sr)2CuO4

International Nuclear Information System (INIS)

Howell, R.H.; Fluss, M.J.; Sterne, P.A.; Kaiser, J.H.; Kitazawa, K.; Kojima, H.

1994-01-01

High-statistics (>4 x 10 8 counts), room-temperature measurements of the electron positron momentum density of La 2-x Sr x CuO 4 have been performed for samples with Sr concentrations of x = 0.0, 0.1, 0.13, and 0.2. These spectra have been analyzed in conjunction with theoretical calculations of the electron positron momentum density. The metallic samples show features consistent with the presence of a Fermi surface, but its evolution with increasing Sr concentration does not follow the predictions of band theory. These results may indicate the effects of electron-electron correlation on the electron momentum distribution in the Cu-O plane. 12 refs., 2 figs

Cu-O superconductors: through a lens, but darkly

International Nuclear Information System (INIS)

Orenstein, J.; Thomas, G.A.; Rapkine, D.H.

1987-01-01

Measurements of reflectivity R, for single crystal samples of La 2 CuO 4 (c-La) and pressed pellets of ceramic La/sub 2-x/Sr/sub x/CuO 4 (LaSr) for x = 0, 0.04, 0.075, 0.175, 0.225 are reported. A plot of R vs log nu for c-La is shown. The samples were cube-like objects approximately 2 mm on a side, which were polished as previously described

An investigation about the improvement of Tc for the n-type superconductor Nd2-xCexCuO4

International Nuclear Information System (INIS)

Wang Cong; Liang Jingkui; Chen Xiaolong; Min Jinrong; Cheng Xiangrong; Zhuang Weidong; Rao Guanghui

1994-01-01

Nd 2-x Ce x CuO 4 (x = 0.12 to 0.18) with T onset = 17 to 26 K is synthesized from the nominal composition of Nd 2-x Ce x CuO 4 + nSrCuO 2 (+nCaCuO 2 ) (n = 1, 2) under standard conditions without high pressure treatment. The sintering temperature, atmosphere, and synthetic procedure are important for the superconductivity of Nd 2-x Ce x CuO 4 . It is difficult to build up n blocks of SrCuO 2 , CaCuO 2 , or CdCuO 2 on Nd 2-x Ce x CuO 4 so as to add CuO 2 layers. In addition, the crystal structure and electrical resistance of Nd 2-x Ce x CuO 4 are studied. (orig.)

Novel CuCr_2O_4 embedded CuO nanocomposites for efficient photodegradation of organic dyes

International Nuclear Information System (INIS)

Mageshwari, K.; Sathyamoorthy, R.; Lee, Jeong Yong; Park, Jinsub

2015-01-01

Graphical abstract: - Highlights: • Novel CuO–CuCr_2O_4 nanocomposites synthesized by reflux condensation method. • Methyl orange and methylene blue dye degradation studied under UV light irradiation. • Nanocomposites characterized by XRD, FESEM, TEM, EDX, UV–vis DRS and PL. • CuCr_2O_4 loading effectively enhanced the catalytic activity of CuO. - Abstract: Novel photocatalyst based on CuO–CuCr_2O_4 nanocomposites was synthesized for different Cr"3"+ concentration by reflux condensation method, and their photocatalytic activity was evaluated by monitoring the photodegradation of methyl orange (MO) and methylene blue dyes (MB) under UV light irradiation. Phase evolution by X-ray diffraction showed monoclinic CuO and tetragonal CuCr_2O_4 as the components of the prepared nanocomposites. Morphological analysis by scanning electron microscope and transmission electron microscope revealed that the incorporation of Cr"3"+ in CuO lattice alters the morphology of CuO from microsphere to cluster shape. Photoluminescence spectra of CuO–CuCr_2O_4 nanocomposites exhibited reduced PL emissions compared to pure CuO, indicating the low recombination rate of photogenerated electrons and holes. As expected, the CuCr_2O_4 loaded CuO showed enhanced photocatalytic activity for MO and MB dyes, and the kinetic studies suggest that the degradation follows pseudo-first-order kinetics. The enhanced photocatalytic activity of CuO–CuCr_2O_4 nanocomposites can be attributed to the presence of CuCr_2O_4 as an electron acceptor, which improves the effective charge separation in CuO.

Experimental aspects of high T/sub c/ superconductors

International Nuclear Information System (INIS)

Gray, K.E.

1988-01-01

The incredible growth of the field of high-T/sub c/ superconductivity makes it difficult for this paper to be extensive or even up-to-date by the time it is published. The references list is in no way complete, but rather gives representative examples known to the author. The discussion in this paper is restricted to the YBa 2 Cu 3 O/sub 7-x/ compound (denoted also as YBCO) which exhibits superconductivity at about 90 K, i.e., above liquid nitrogen temperature of 77 K, since such an increase in operating temperature seems to be the major reason for considering these materials for rf applications. An overview of the various fabrication methods is given, which include bulk samples made by ceramic processing and thin films made by MBE/electron beam co-evaporation/co-sputtering/pulsed excimer laser evaporation/etc. Particularly interesting examples include single crystals and epitaxial thin films. Although these are not expected to be useful in cavity applications, they provide them with the best information on the intrinsic properties of the material, from which they can project its potential usefulness if these properties can be duplicated using more practical fabrication methods. This brief review will include examples of microstructure, traditional superconducting properties like T/sub c/, H/sub c2/ and J/sub c/, specific heat, thermal conductivity, photoemission, infra-red(ir) reflectance, tunneling and Raman scattering. Four important considerations for rf cavity work will emerge: the transport critical current density; the energy gap; impurity phases; and potential surface problems especially related to oxygen deficiencies. 37 references, 8 figures

Distinct Nature of Static and Dynamic Magnetic Stripes in Cuprate Superconductors

DEFF Research Database (Denmark)

Jacobsen, H.; Holm, S. L.; Lăcătuşu, M. E.

2018-01-01

We present detailed neutron scattering studies of the static and dynamic stripes in an optimally doped high-Temperature superconductor, La2CuO4+y. We observe that the dynamic stripes do not disperse towards the static stripes in the limit of vanishing energy transfer. Therefore, the dynamic stripes...

The oxygen-isotope effect on the in-plane penetration depth in underdoped Y{sub 1-x} Pr{sub x} Ba{sub 2} Cu{sub 3} O{sub 7-{delta}} as revealed by muon-spin rotation

Energy Technology Data Exchange (ETDEWEB)

Khasanov, R [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Shengelaya, A [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Conder, K [Laboratory for Neutron Scattering, ETH Zuerich and PSI Villigen, CH-5232 Villigen PSI (Switzerland); Morenzoni, E [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Savic, I M [Faculty of Physics, University of Belgrade, 11001 Belgrade (Yugoslavia); Keller, H [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland)

2003-01-22

The oxygen-isotope ({sup 16}O/{sup 18}O) effect (OIE) on the in-plane penetration depth {lambda}{sub ab} (0) in underdoped Y{sub 1-x} Pr{sub x} Ba{sub 2} Cu{sub 3} O{sub 7-{delta}} was studied by means of muon-spin rotation. A pronounced OIE on {lambda}{sub ab}{sup -2} (0) was observed with a relative isotope shift of {delta}{lambda}{sub ab}{sup -2} /{lambda} {sub ab}{sup -2} = -5(2)% for x=0.3 and -9(2)% for x=0.4. The OIE exponents of T{sub c} and of {lambda}{sub ab}{sup -2} (0) exhibit a relation that appears to be generic for cuprate superconductors. (letter to the editor)

Aurivillius-Popper mixed superconductors in BiO--CuO--(Sr/sub 0.5/, Ca/sub 0.5/)O system

International Nuclear Information System (INIS)

Fukuhara, M.; Bhalla, A.S.; Mulay, L.N.; Newnham, R.E.

1989-01-01

We report the effect of inhomogeneities on the electric resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO--Cuo--(Sr/sub 0.5/, Ca/sub 0.5/)O system and propose a crystal structure of the major phase having highest T/sub c/. Nominal Aurivillius compositions with molar ratios of BiO/(Sr/sub 0.5/, Ca/sub 0.5/)O = 1/2 are superconductors with T/sub c/ ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. T/sub c/ increases with decreasing of the c lattice parameter. An oxide BiSrCaCu 2 O/sub x/ (n = 2) shows a maximum T/sub c/ value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi 2 Sr 2 CaCu 2 O/sub x/ consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain

Distinct Nature of Static and Dynamic Magnetic Stripes in Cuprate Superconductors

Science.gov (United States)

Jacobsen, H.; Holm, S. L.; Lǎcǎtuşu, M.-E.; Rømer, A. T.; Bertelsen, M.; Boehm, M.; Toft-Petersen, R.; Grivel, J.-C.; Emery, S. B.; Udby, L.; Wells, B. O.; Lefmann, K.

2018-01-01

We present detailed neutron scattering studies of the static and dynamic stripes in an optimally doped high-temperature superconductor, La2 CuO4 +y . We observe that the dynamic stripes do not disperse towards the static stripes in the limit of vanishing energy transfer. Therefore, the dynamic stripes observed in neutron scattering experiments are not the Goldstone modes associated with the broken symmetry of the simultaneously observed static stripes, and the signals originate from different domains in the sample. These observations support real-space electronic phase separation in the crystal, where the static stripes in one phase are pinned versions of the dynamic stripes in the other, having slightly different periods. Our results explain earlier observations of unusual dispersions in underdoped La2 -xSrx CuO4 (x =0.07 ) and La2 -xBax CuO4 (x =0.095 ).

Chemical bond properties and Mossbauer spectroscopy in (La1-xMx)2CuO4 (M=Ba, Sr)

Institute of Scientific and Technical Information of China (English)

无

2002-01-01

By using the average band-gap model, the chemical bond properties of (La1-x Mx)2CuO4(M=Ba, Sr) were calculated . The calculated covalencies for Cu(O and La(O bond in the compounds are 0.3 and 0.03 respectively. M?ssbauer isomer shifts of 57Fe doped in La2CuO4 and 119Sn doped in La2CuO4 were calculated by using the chemical surrounding factor defined by covalency and electronic polarizability. Four valence state tin and three valence iron sites were identified in 57Fe and 119Sn doped La2CuO4.

Crystal structure of Nd4Cu2O7

International Nuclear Information System (INIS)

Pederzolli, D.R.; Attfield, J.P.

1998-01-01

The structure of Nd 4 Cu 2 O 7 (A2/m, a = 8.449 A, b = 3.759 A, c = 12.601 A, β = 109.57 ), prepared by topotactic reduction of the high-T c superconductor parent phase Nd 2 CuO 4 , has been determined from time-of-flight neutron powder diffraction data revealing a new oxygen vacancy-ordered arrangement containing cooperatively distorted Cu 2 O 3 planes in which 2- and 4- coordinate Cu - sites are present. (orig.)

Vortex states of Tl2Ba2CuO6+δ studied via 205Tl NMR at 2 tesla

International Nuclear Information System (INIS)

Itoh, Yutaka; Michioka, Chishiro; Yoshimura, Kazuyoshi; Hayashi, Akihiko; Ueda, Yutaka

2005-01-01

We report a 205 Tl NMR study of vortex states in an aligned polycrystalline sample of an overdoped high-T c superconductor, Tl 2 Ba 2 CuO 6+δ (Tc - 85 K), at a magnetic field of 2 T along the c axis. We observed an imperfect vortex lattice, so-called Bragg glass, at T=5 K, the coexistence of vortex solid and vortex liquid between 10 and 60 K, and vortex melting between 65 and 85 K. No evidence for local antiferromagnetic ordering at vortex cores was found for our sample. (author)

Novel phenomenon of magnetism and superconductivity in Fe-doped superconductor Bi{sub 4-x}Fe{sub x}O{sub 4}S{sub 3} (0 ≤ x ≤ 0.1)

Energy Technology Data Exchange (ETDEWEB)

Li, Qing [Shanghai University, Department of Physics, Shanghai (China); Shanghai University, Materials Genome Institute, Shanghai (China); Wang, Difei; Yu, Chuan; Yin, Xunqing; Kang, Jian; Cheng, Cheng; Deng, Dongmei; Jing, Chao [Shanghai University, Department of Physics, Shanghai (China); Feng, Zhenjie; Cao, Shixun; Zhang, Jincang [Shanghai University, Department of Physics, Shanghai (China); Shanghai University, Materials Genome Institute, Shanghai (China); Shanghai Key Laboratory of High Temperature Superconductors, Shanghai (China); Chu, Hao [California Institute of Technology, Department of Applied Physics, Pasadena, CA (United States); Li, Xiaolong [Chinese Academy of Sciences, Shanghai Institute of Applied Physics, Shanghai (China)

2017-06-15

We report the effects of Fe doping on the BiS{sub 2}-based superconductor Bi{sub 4}O{sub 4}S{sub 3}. It has been found that the superconducting transition temperature (T{sub C}{sup onset}) is slightly enhanced by Fe doping. The magnetic susceptibility results reveal the coexistence of superconductivity and long-range ferrimagnetism in these samples. A new magnetic transition temperature T{sub V} (Verwey transition) from the M-T curves at ∝112 K is observed. The isothermal magnetization curves (M-H) indicate a weak ferrimagnetism, which is probably due to the antiparallel ordering of Fe{sup 2+} and Fe{sup 3+} magnetic moments. The coexistence of superconductivity and ferro/ferrimagnetism makes bismuth oxysulfide superconductor a platform for understanding superconductivity from a new perspective. (orig.)

Magnetic excitations in La2CuO4

International Nuclear Information System (INIS)

Singh, R.R.P.

1989-01-01

The authors compare the experimentally observed magnetic excitations in La 2 CuO 4 with those calculated for a square lattice spin-1/2 Heisenberg antiferromagnet. They find that the short-wavelength spin-pair excitation spectrum deduced from light scattering, and the long wavelength spin- wave dispersion deduced from neutron scattering are both consistent with a nearest neighbor model with the exchange constant J of about 1500 K

X-ray photo-emission studies of Cu1-xTlxBa2Ca3Cu4O12-y superconductor thin films

International Nuclear Information System (INIS)

Khan, Nawazish A.; Mumtaz, M.; Ahadian, M.M.; Iraji-zad, Azam

2006-01-01

X-ray photo-emission spectroscopy (XPS) studies of Cu 1-x Tl x Ba 2 Ca 3 Cu 4 O 12-y superconductor thin films have been carried out for understanding the mechanism of superconductivity and to find out the reasons for the increase of zero resistivity critical temperature T c (R = 0) with post-annealing in a nitrogen atmosphere. It is observed from these studies that reduction of charge state of thallium is a source of doping of carriers to the CuO 2 planes. The reduced charge state of thallium (i.e. Tl 1+ ) promotes lower oxygen concentration in the charge reservoir layer, which possibly results in movement of electrons to the conducting CuO 2 planes. The higher density of electrons in the CuO 2 planes optimizes the hole concentration 'n p ' in these planes. The reduced charge state of thallium in the Cu 1-x Tl x Ba 2 O 4-δ charge reservoir layer is also supported by a shift of the Ba 3d 5/2 and Ba 3d 3/2 XPS lines to lower binding energies with post-annealing in nitrogen atmosphere. Moreover, the movement of the valance band spectrum to lower binding energies suggested that the electronic density of states changes in the valance band with the post-annealing in nitrogen, which possibly becomes a source of doping of carriers to the CuO 2 planes. The increased doping of electrons to the CuO 2 planes optimizes the Fermi-vector K F and Fermi-velocity V F of the carriers and increases the T c (R = 0) of final compound

Raman spectra of Hg-based superconductors: Effect of oxygen defects

Science.gov (United States)

Zhou, Xingjiang; Cardona, M.; Chu, C. W.; Lin, Q. M.; Loureiro, S. M.; Marezio, M.

1996-09-01

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa2Can-1CunO2n+2+δ (n=1, 2, 3, 4, and 5) high-Tc superconductor family. A systematic evolution of the spectrum, which mainly involves oxygen-related phonons around 590, 570, 540, and 470 cm-1, with an increasing number of CuO2 layers, has been observed. Local laser annealing measurements clearly demonstrate that all these phonons are closely related to interstitial oxygen in the HgOδ planes. The origin of the spectrum evolution with the number of CuO2 layers lies in the variation of interstitial oxygen content.

Evidence for a pseudogap above T{sub c} in underdoped superconductors

Energy Technology Data Exchange (ETDEWEB)

Mesot, J; Boettger, G; Furrer, A [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Berastegui, P; Mutka, H [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

1997-09-01

Our measurements of the temperature dependence of the relaxation rate of crystal field excitations in underdoped high temperature superconductors show clear evidences for the opening of a pseudogap in the normal state. The critical temperature related to the opening of the pseudogap appears to be extremely dependent upon the energy window at which the static susceptibility is being probed. (author) 2 figs., 4 refs.

Optical properties of La2CuO4 and La2−xCaxCuO4 crystallites in UV–vis–NIR region synthesized by sol–gel process

International Nuclear Information System (INIS)

Li Yifeng; Huang Jianfeng; Cao Liyun; Wu Jianpeng; Fei Jie

2012-01-01

La 2 CuO 4 and La 2−x Ca x CuO 4 crystallites were prepared via a simple sol–gel process. The as-prepared La 2 CuO 4 and La 2 −x Ca x CuO 4 crystallites were characterized by X-ray diffraction, transmission electron microscope and UV–vis–NIR spectra. Results show that the grain size of La 2 CuO 4 crystallites increases with the increase of heat treatment temperature from 600 °C to 800 °C. Optical properties show that La 2 CuO 4 crystallites have broad absorption both in the UV–vis region and in the NIR region. The band gap of the as-prepared crystallites decreases from 1.367 eV to 1.284 eV with the increase of calcination temperature from 600 °C to 800 °C. In the series of La 2−x Ca x CuO 4 compounds (x = 0.05, 0.08, 0.10, 0.12, 0.15 and 0.20), all of the samples exhibit an orthogonal crystal structure and the solubility limit of Ca 2+ in La 2 CuO 4 is within the range of x = 0.12–0.15. In the whole UV–vis–NIR region, La 2−x Ca x CuO 4 crystallites exhibit a broad absorption and the corresponding band gap first increases and then decreases with increasing of Ca 2+ content. - Highlights: ► The optical band gap can be tuned by adjusting the grain size and Ca 2+ content. ► La 2 CuO 4 crystallites exhibit a broad absorption band both in the UV–vis region and in the NIR region. ► The band gap increases from 1.284 eV to 1.319 eV with the decrease of heat treatment temperature. ► In the whole UV–vis–NIR region, the La 2−x Ca x CuO 4 crystallites displayed a broad absorption. ► The band gap of La 2−x Ca x CuO 4 increases linearly with doping level when 0 ≤ x ≤ 0.12.

Superconductivity in La1.56Sr0.44CuO4/La2CuO4 Superlattices

International Nuclear Information System (INIS)

Bozovic, I.; Suter, A.; Morenzoni, E.; Prokscha, T.; Luetkens, H.; Wojek, B.M.; Logvenov, G.; Gozar, A.

2011-01-01

Superlattices of the repeated structure La 1.56 Sr 0.44 CuO 4 /La 2 CuO 4 (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T(prime) c 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy μSR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account the layered structure and the difference in the chemical potential between LCO and LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could estimate a strict upper limit of the London penetration depth to 380 nm in these superlattices. The temperature dependence of the muon depolarization rate in field cooling experiments is very similar to what is observed in intercalated BSCCO and suggests that vortex-vortex interaction is dominated by electromagnetic coupling but negligible Josephson interaction.

Collective Dynamics and Strong Pinning near the Onset of Charge Order in La1.48Nd0.4Sr0.12CuO4

Science.gov (United States)

Baity, P. G.; Sasagawa, T.; Popović, Dragana

2018-04-01

The dynamics of charge-ordered states is one of the key issues in underdoped cuprate high-temperature superconductors, but static short-range charge-order (CO) domains have been detected in almost all cuprates. We probe the dynamics across the CO (and structural) transition in La1.48Nd0.4Sr0.12CuO4 by measuring nonequilibrium charge transport, or resistance R as the system responds to a change in temperature and to an applied magnetic field. We find evidence for metastable states, collective behavior, and criticality. The collective dynamics in the critical regime indicates strong pinning by disorder. Surprisingly, nonequilibrium effects, such as avalanches in R , are revealed only when the critical region is approached from the charge-ordered phase. Our results on La1.48Nd0.4Sr0.12CuO4 provide the long-sought evidence for the fluctuating order across the CO transition, and also set important constraints on theories of dynamic stripes.

Oxygen partial pressure treatment of the electron-doped superconductor (Nd0.92Ce0.08)2CuO4-δ

International Nuclear Information System (INIS)

Suzuki, M.; Ami, T.; Isobe, M.; Tanaka, M.

1992-01-01

The condition under which the superconducting phase in (Nd 1-x Ce x ) 2 CuO 4-δ with x=0.08 is obtained was determined in the 1/T-log Po 2 phase diagram using an oxygen partial pressure (Po 2 ) controllable heat treatment system in conjunction with a quench system. The superconducting area is very narrow and is adjacent to the area of significant decomposition. We determined that the a-axis lattice constant increased slightly as the character of the electric conduction changed from semiconductive to metallic. (orig.)

Oxygen partial pressure treatment of the electron-doped superconductor (Nd0.92Ce0.08)2CuO4-δ

International Nuclear Information System (INIS)

Suzuki, M.; Ami, T.; Isobe, M.; Tanaka, M.

1992-01-01

The condition under which the superconducting phase in (Nd 1-x Ce x ) 2 CuO 4-δ with x = 0.08 is obtained was determined in the 1/T-log Po 2 phase diagram using an oxygen partial pressure (Po 2 ) controllable heat treatment system in conjunction with a quench system. The superconducting area is very narrow and is adjacent to the area of significant decomposition. In this paper, the authors determined that the a-axis lattice constant increased slightly as the character of the electric conduction changed from semiconductive to metallic

Larmor diffraction in the ferromagnetic superconductor UGe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Ritz, Robert; Pfleiderer, Christian [Physik Department E21, TU Muenchen, D-85748 Garching (Germany); Sokolov, Dmitry; Huxley, Andrew [School of Physics and Astronomy, Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Keller, Thomas [MPI fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart (Germany)

2010-07-01

Larmor Diffaction (LD) is a neutron resonance spin-echo technique which allows the study of the lattice constant as well the distribution of lattice constants. It was traditionally thought that neutron spin-echo measurements cannot be used in materials such as superconductors or ferromagnets, because they strongly depolarize a polarized neutron beam. In UGe{sub 2} we are able to demonstrate that this technique may be applied in ferromagnetic superconductors with a magnetic Ising anisotropy. UGe{sub 2} exhibits two ferromagnetic phases which are separated by a transition at temperature T{sub x}. With increasing hydrostatic pressure superconductivity emerges at the pressure for which T{sub x} is suppressed. Using LD we studied the temperature dependence of the lattice constant as well as the distribution of lattice constants for all three axis of UGe{sub 2} down to 0.5 K and at pressures up to 12 kbar.

Chemical Bonding in Tl Cuprates Studied by X-Ray Photoemission

Energy Technology Data Exchange (ETDEWEB)

Lao, J.Y.; Overmyer, D.L.; Ren, Z.F.; Siegal, M.P.; Vasquez, R.P.; Wang, J.H.

1999-04-05

Epitaxial thin films of the Tl cuprate superconductors Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, and TL{sub 0.78}Bi{sub 0.22}Ba{sub 0.4}Sr{sub 1.6}Ca{sub 2}Cu{sub 3}O{sub 9{minus}{delta}} are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}, comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E{sub s}-E{sub m}) and a lower intensity ratio (I{sub s}/I{sub m}) are found to correlate with higher values of T{sub c}. Analysis of these spectra within a simple configuration interaction model suggests that higher values of T{sub c} are related to low values of the O 2p {r_arrow} Cu 3d charge transfer energy. In the O 1s region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by Ba{sup 2+} ions. For samples near optimum doping, maximum T{sub c} is observed to occur when the Tl 4f{sub 7/2} binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher Tl 4f{sub 7/2} binding energies, corresponding to formal oxidation states nearer Tl{sup 1+}, are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the O 1s signal associated with Tl-O bonding.

Chemical bonding in Tl cuprates studied by x-ray photoemission

Energy Technology Data Exchange (ETDEWEB)

Vasquez, R.P. [Center for Space Microelectronics Technology, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099 (United States); Siegal, M.P.; Overmyer, D.L. [Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States); Ren, Z.F.; Lao, J.Y.; Wang, J.H. [Materials Synthesis Laboratory, Department of Chemistry, State University of New York, Buffalo, New York 14260-3000 (United States)

1999-08-01

Epitaxial thin films of the Tl cuprate superconductors Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}, Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}, and Tl{sub 0.78}Bi{sub 0.22}Ba{sub 0.4}Sr{sub 1.6}Ca{sub 2}Cu{sub 3}O{sub 9{minus}{delta}} are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}, comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu 2p spectra, a larger energy separation between the satellite and main peaks (E{sub s}{minus}E{sub m}) and a lower intensity ratio (I{sub s}/I{sub m}) are found to correlate with higher values of T{sub c}. Analysis of these spectra within a simple configuration interaction model suggests that higher values of T{sub c} are related to low values of the O&hthinsp;2p{r_arrow}Cu&hthinsp;3d charge transfer energy. In the O&hthinsp;1s region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by Ba{sup 2+} ions. For samples near optimum doping, maximum T{sub c} is observed to occur when the Tl 4f{sub 7/2} binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher Tl&hthinsp;4f{sub 7/2} binding energies, corresponding to formal oxidation states nearer Tl{sup 1+}, are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the O&hthinsp;1s signal associated with Tl-O bonding. {copyright} {ital 1999} {ital The American Physical Society}

Probing the CuO planes with positrons in high Tc cuprates: theoretical predictions

International Nuclear Information System (INIS)

Barbiellini, B.; Jarlborg, T.; Massidda, S.; Peter, M.

1995-01-01

Positron annihilation spectroscopy is a useful tool to investigate the Fermi surface in high T c superconductors. To study the physics of the copper-oxygen subsystem that forms the Cu-O layers, it is important to provide theoretical predictions, on materials where there is a large overlap between the positron and the interesting Cu-O planes. We have performed first-principle electronic structure calculations obtained using the linear muffin-tin orbital and the full-potential linearized augmented plane wave methods. The positron charge distributions and their sensitivity to different potentials are calculated. Secondly, we have computed the annihilation rates and the electron-positron momentum density in order to give predictions of the Fermi surface signals. (orig.)

Electrical and thermoluminescence properties of γ-irradiated La2CuO4 crystals

Science.gov (United States)

El-Kolaly, M. A.; Abd El-Kader, H. I.; Kassem, M. E.

1994-12-01

Measurements of the electrical properties of unirradiated as well as ?-irradiated La2CuO4 crystals were carried out at different temperatures in the frequency range of 0.1-100 kHz. Thermoluminescence (TL) studies were also performed on such crystals in the temperature range of 300-600K. The conductivity of the unirradiated La2CuO4 crystals were found to obey the power law frequency dependence at each measured temperature below the transition temperature (Tc = 450K). The activation energies for conduction and dielectric relaxation time have been calculated. The TL response and the dc resistance were found to increase with ?-irradiation dose up to 9-10 kGy. The results showed that the ferroelastic domain walls of La2CuO4 crystal as well as its TL traps are sensitive to ?-raditaion. This material can be used in radiation measurements in the range 225 Gy-10 kGy.

Cu-O network dependence of optical charge-transfer gaps and spin-pair excitations in single-CuO2-layer compounds

International Nuclear Information System (INIS)

Tokura, Y.; Koshihara, S.; Arima, T.; Takagi, H.; Ishibashi, S.; Ido, T.; Uchida, S.

1990-01-01

Spectra of optical conductivity and magnon Raman scattering have been investigated in single crystals of a parent family of cuprate superconductors with various types of Cu-O single-layer networks. The analysis of the spectra shows the systematic dependence of the charge-transfer gaps and covalent character of Cu-O bonds on the pattern of the Cu-O network, while the spin-exchange energy is rather convergent for all the single-CuO 2 -sheet compounds

Strongly disordered superconductors

International Nuclear Information System (INIS)

Muttalib, K.A.

1982-01-01

We examine some universal effects of strong non-magnetic disorder on the electron-phonon and electron-electron interactions in a superconductor. In particular we explicitly take into account the effect of slow diffusion of electrons in a disordered medium by working in an exact impurity eigenstate representation. We find that the normal diffusion of electrons characterized by a constant diffusion coefficient does not lead to any significant correction to the electron-phonon or the effective electron-electron interactions in a superconductor. We then consider sufficiently strong disorder where Anderson localization of electrons becomes important and determine the effect of localization on the electron-electron interactions. We find that due to localization, the diffusion of electrons becomes anomalous in the sense that the diffusion coefficient becomes scale dependent. This results in an increase in the effective electron-electron interaction with increasing disorder. We propose that this provides a natural explanation for the unusual sensitivity of the transition temperature T/sub c/ of the high T/sub c/ superconductors (T/sub c/ > 10 0 K) to damage effects

Structural phase transformation in K2SeO4

International Nuclear Information System (INIS)

Iizumi, M.; Axe, J.D.; Shirane, G.; Shimaoka, K.

1977-01-01

Successive phase transformations in K 2 SeO 4 at T 1 = 130 K and T/sub c/ = 93 K were studied by the neutron-scattering technique. The superlattice reflections in the intermediate phase were found to be incommensurate with the lattice periodicity. The wave vector characterizing the reflections is q/sub delta/ = (1-delta) a*/3 with delta = 0.07 at 122.5 K. The deviation delta decreases with decreasing temperature with an apparently discontinuous jump to zero at T/sub c/. Below this temperature, the crystal remains commensurate and is known to be ferroelectric. The incommensurate-commensurate transition and the simultaneous occurrence of the commensurate phase and the spontaneous polarization are discussed using a Landau-type expansion of the free energy in which a term proportional to Q 3 (q/sub delta/) P/sub z/ (q 3 /sub delta/) plays an essential role in driving the incommensurate-commensurate phase transformation and in inducing the spontaneous polarization. Here, Q (q/sub delta/) is the amplitude of the primary atomic displacements with wave vector q/sub delta/ and P/sub z/(q 3 /sub delta/) is the polarization wave with wave vector q 3 /sub delta/ = 3delta (a*/3) and becomes the macroscopic polarization below T/sub c/. Above T/sub i/, a Σ 2 optic-phonon branch along (xi,0,0) shows a striking softening and ω/sub j/(q) for q approx. (1/3,0,0) tends to zero at T/sub i/. The softening results from a temperature-dependent decrease of the interlayer forces with ranges a/2 and a (a is one unit-cell length along the a axis) in the presence of strong and persisting forces with a range 3a/2. The intensities of the soft phonon were measured about different reciprocal-lattice points and were used to determine the nature of the soft-phonon mode and suggest a coupled translation of potassium ions with rotational motion of SeO 4 groups to be the origin of the lattice instability

Electronic structure of (La,Sr)2CuO4 and Ba0.6K0.4BiO3

International Nuclear Information System (INIS)

Howell, R.H.; Sterne, P.A.; Fluss, M.J.; Kaiser, J.H.; Kitazawa, K.; Kojima, H.; Mosley, W.D.; Dykes, J.W.; Shelton, R.N.

1995-01-01

We have measured and calculated the electron-positron momentum distribution of La 2-x Sr x CuO 4 samples for Sr concentrations of 0, 0.1,0.13, and 0.2 and Ba 0.6 K 0.4 BiO 3 . The momentum distribution of all samples contained features derived from the overlap of the positron distribution with the valence electrons. In addition, discontinuities typical of a Fermi surface are seen in the superconducting samples. The form and position of these features are in general agreement with band theory for both La 2-x Sr x CuO 4 and Ba 0.6 K 0.4 BiO 3 . However the evolution of the Fermi surface with doping in La 2-x Sr x CuO 4 differed significantly from expectations based on single electron band theories. (orig.)

Magnetic field dependence of ultrasound velocity in high-Tc superconductors

International Nuclear Information System (INIS)

Higgins, M.J.; Goshorn, D.P.; Bhattacharya, S.; Johnston, D.C.

1989-01-01

The magnetic field dependence of ultrasound velocity in the superconductor La 1.8 Sr 0.2 CuO 4-y is studied. The sound velocity anomaly near T c is shown to be unambiguously related to superconductivity. Below T c , the sound velocity is found to be sensitive to the dynamics of a pinned flux lattice. A combination of sound velocity and magnetization measurements suggests three regimes of pinning behavior. A generic pinning ''phase diagram'' is obtained in the superconducting state. An anomalous peak effect in the magnetization is also observed at intermediate field strengths

X-ray photoelectron spectroscopy of high-temperature superconductor clean surfaces and interfaces

International Nuclear Information System (INIS)

Hill, D.M.

1989-01-01

X-ray photoelectron spectroscopy was used to determine the characteristic spectra for the high temperature superconductors La 1.85 Sr 0.15 CuO 4 , YBa 2 Cu 3 O 7-x , and Bi 2 Sr 2-x Ca 1+x Cu 2 O 8+y and their impurity phases. The oxidation state of Cu in all of these materials was predominantly Cu 2+ . The O 1s emission for clean surfaces was a single broad peak near 529 eV derived from emission from inequivalent O sites in the superconductors. The valence bands were a -6 eV wide manifold of Cu 3d-O 2p hybrid bands in the ∼ 1-7 eV binding energy range, with very low emission at E F arising from antibonding Cu 3d-O 2p orbitals. Emission from grain boundary and other impurity phases appeared at 531 eV for the O 1s core level, and in general ∼ 1-2 eV higher energy than the superconductor peak for other core levels except for Cu 2p. Impurity phases appeared in the valence bands as a shoulder at ∼ 5 eV. The amount of impurities detected was shown to be dependent on the fracture properties of the superconductors. All of the materials were shown to be stable under vacuum. The products and spatial extent of chemical reactions with Ag, Al, Al oxide, Au, Bi, Bi oxide, CaF 2 , Cu, Fe, Si, and Si oxide overlayers on these materials also were examined. Au, CaF 2 , and metal oxides deposited by activated oxidation during evaporation were non-reactive and non-disruptive of the superconductor surfaces. Ag overlayers were unique in that they disrupted the superconductor during deposition, but exhibited no evidence of any chemical reactions. Overlayers with an affinity for oxygen withdrew O from the superconductor. The O loss occurred preferentially from Cu atoms in the superconductor and disrupted the planar bonding structure

Irradiation effects in superconductor oxides. Effets d'irradiation dans les oxydes supraconducteurs

Energy Technology Data Exchange (ETDEWEB)

Rullier-Albenque, F; Konczykowski, M [CEA-Ecole Polytechnique, 91 - Palaiseau (France). Lab. d' Etudes des Solides Irradies

1993-01-01

Several effects of irradiation on the 92 K - oxide superconductor YBa[sub 2]Cu[sub 3]O[sub 7] are reported. Whatever irradiation type, the critical temperature T[sub c] is found to decrease and the resistivity to increase. At sufficiently high damage levels, YBa[sub 2]Cu[sub 3]O[sub 7] is no longer superconducting and even displays a semiconducting-like behaviour. The alterations of superconducting properties are clearly related to oxygen defects - in the CuO[sub 2] planes or CuO chains... but we have shown experimentally that copper defects are also important. Magnetic properties of YBa[sub 2]Cu[sub 3]O[sub 7] in mixed state are also very sensitive to irradiation. By pinning the flux lines, irradiation defects can considerably increase the critical current density j[sub c]. At present, irradiations by highly energetic heavy ions (6 GeV Pb for instance), which produce cylindrical tubes of amorphous material (latent tracks) throughout the whole thickness of the samples, are probably the most efficient way to enhance j[sub c]. (Author). 18 refs., 7 figs.

Optical excitations in CuO2-sheets doped and undoped with electrons

International Nuclear Information System (INIS)

Tokura, Y.; Arima, T.; Koshihara, S.; Takagi, H.; Ido, T.; Ishibashi, S.; Uchida, S.

1989-01-01

This paper reports optical reflectance spectra measured on single crystals of parent families of high T c copper oxide compounds with single-layered CuO 2 -sheets, which clearly show the strong transitons across the charge-transfer (CT) gaps at 1.5-2.0 eV in various types of CuO 2 -sheets. The carrier-doping effects on the CT excitations have been investigated on the Sr-doped La 2 CuO 4 and Ce-doped Nd 2 O 4 crystals

Rotational loss of a ring-shaped flywheel supported by high T{sub c} superconducting levitation

Energy Technology Data Exchange (ETDEWEB)

Teshima, Hidekazu [Nippon Steel Corp., Kawasaki, Kanagawa (Japan). Advanced Materials and Technology Research Labs.; Tawara, Taichi; Shimada, Ryuichi

1997-08-01

This paper describes the experimental results for the rotational loss of a ring-shaped flywheel supported by high T{sub c} superconducting levitation. Superconducting levitation is appropriate for rotating a ring-shaped flywheel which has neither shaft nor hub because it is a non-contact and automatically stable levitation without any control systems. The rotational loss has been investigated using a small-scaled experimental machine consisting of 16 bulk superconductors 46 mm in diameter and a ring-shaped flywheel about 300 mm in diameter. The rotational loss decreased as the levitation gap height increased. In low-speed rotational regions, the rotational loss was in proportion to the rotation speed and depended more on the levitation gap. In high-speed rotational regions, the rotational loss was in proportion to the third power of the rotation speed and depended less on the levitation gap. The cubic rotational loss in He was reduced to one-fifth of that in air. The magnetic field pinned in bulk superconductors induces a loss in the materials composing the ring-shaped flywheel. The rotational loss of a ring-shaped flywheel supported by superconducting levitation can be reduced by improving the uniformity of the magnetic fields along the ring, enlargement of the bulk superconductor(s), and densely arranging the bulk superconductors. (author)

Sr{sub 2}RuO{sub 4} at high uniaxial strain

Energy Technology Data Exchange (ETDEWEB)

Steppke, Alexander; Hicks, Clifford [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Zhao, Lishan; Brodsky, Daniel; Barber, Mark; Mackenzie, Andrew [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); University of St. Andrews (United Kingdom); Gibbs, Alexandra [Max Planck Institute for Solid State Research, Stuttgart (Germany); Maeno, Yoshiteru [Kyoto University (Japan)

2016-07-01

We applied high anisotropic strains to high-quality single crystals of the superconductor Sr{sub 2}RuO{sub 4}, to gain information on the influence of anisotropic Fermi surface distortions on its superconductivity. Due to proximity to a van Hove singularity, one of the Fermi surfaces distorts particularly strongly in response to anisotropic strain. The superconducting properties also vary strongly: we show susceptibility and resistivity data indicating that T{sub c} more than doubles as strain is applied, and passes through a sharp peak. Similarly, the upper critical field H{sub c2} for fields both parallel and perpendicular to the crystallographic c axis increases substantially. For fields perpendicular to the c axis, there is strongly hysteretic behaviour at low temperatures, that may be due to Pauli limiting.

Screen printed Y and Bi-based superconductors

Science.gov (United States)

Haertling, Gene H.; Hsi, Chi-Shiung

1992-01-01

High T(sub c) superconducting thick film was prepared by screen printing process. Y-based (YBa2Cu3O(7 - x)) superconducting thick films were printed on 211/Al2O3, SNT/Al2O3, and YSZ substrates. Because of poor adhesion of the superconducting thick films to 211/Al2O3 and SNT/Al2O3 substrates, relatively low T(sub c) and J(sub c) values were obtained from the films printed on these substrates. Critical temperatures of YBa2Cu3O(7 - x) thick films deposited on 211/Al2O3 and SNT/Al2O3 substrates were about 80 K. The critical current densities of these films were less than 2 A/cm(exp 2). Higher T(sub c) and J(sub c) films were printed on the YSZ substrates; T(sub c) = 86.4 K and J(sub c) = 50.4 A/cm(exp 2). Multiple lead samples were also prepared on the YSZ substrates. These showed lower T(sub c) and J(sub c) values than plain samples. The heat treatment conditions of the multiple lead samples are still under investigation. Bi-based superconductor thick films have been obtained so far. Improving the superconducting properties of the BSCCO screen printed thick films will be emphasized in future work.

Observation of an hexatic vortex glass in flux lattices of the high-Tc superconductor Bi sub 2. 1 Sr sub 1. 9 Ca sub 0. 9 Cu sub 2 O sub 8+. delta

Energy Technology Data Exchange (ETDEWEB)

Bishop, D J; Gammel, P L; Murray, C A [AT and T Bell Labs., Murray Hill, NJ (USA); Mitzi, D B; Kapitulnik, A [Stanford Univ., CA (USA)

1991-02-01

We report observation of hexatic order in Abrikosov flus lattices in very clean crystals of the high-Tc superconductor Bi{sub 2.1}Sr{sub 1.9}Ca{sub 0.9}Cu{sub 2}O{sub 8+{delta}} (BSCCO). Our experiments consist of in situ magnetic decoration of the flux lattice at 4.2 K. Analysis of the decoration images shows that the positional order decays exponentially with a correlation length of a few lattice constants while the orientational order persists for hundreds of lattice constants and decays algebraically with an exponent {eta}{sub 6}=0.6{+-}0.01. Our results confirm recent theoretical speculation that the positional order should be far more sensitive to disorder than the orientational order and that the low-temperature ordered phase of the flux lines in these systems might be an hexatic glass. (orig.).

Positron annihilation studies in the high-temperature superconductors YBa2Cu3Osub(7-x) and HoBa2Cu3Osub(7-x)

International Nuclear Information System (INIS)

Mandal, P.; Poddar, A.; Nambissan, P.M.G.; Choudhury, P.; Ghosh, B.; Sen, P.; Majumdar, C.K.

1988-01-01

In the high-Tsub(c) superconductors YBa 2 Cu 3 Osub(7-x) and HoBa 2 Cu 3 Osub(7-x) the Doppler-broadened positron annihilation lineshape parameter is studied as a function of temperature. Anomalies are detected around the transition temperature found by resistance measurements, giving indirect support for an electronic mechanism for superconductivity. The positron lifetimes in these compounds are measured at room temperature and are found to be similar. The origins of the several lifetimes found and their intensities are discussed. (author)

Porous SnO2-CuO nanotubes for highly reversible lithium storage

Science.gov (United States)

Cheong, Jun Young; Kim, Chanhoon; Jung, Ji-Won; Yoon, Ki Ro; Kim, Il-Doo

2018-01-01

Facile synthesis of rationally designed structures is critical to realize a high performance electrode for lithium-ion batteries (LIBs). Among different candidates, tin(IV) oxide (SnO2) is one of the most actively researched electrode materials due to its high theoretical capacity (1493 mAh g-1), abundance, inexpensive costs, and environmental friendliness. However, severe capacity decay from the volume expansion and low conductivity of SnO2 have hampered its use as a feasible electrode for LIBs. Rationally designed SnO2-based nanostructures with conductive materials can be an ideal solution to resolve such limitations. In this work, we have successfully fabricated porous SnO2-CuO composite nanotubes (SnO2-CuO p-NTs) by electrospinning and subsequent calcination step. The porous nanotubular structure is expected to mitigate the volume expansion of SnO2, while the as-formed Cu from CuO upon lithiation allows faster electron transport by improving the low conductivity of SnO2. With a synergistic effect of both Sn and Cu-based oxides, SnO2-CuO p-NTs deliver stable cycling performance (91.3% of capacity retention, ∼538 mAh g-1) even after 350 cycles at a current density of 500 mA g-1, along with enhanced rate capabilities compared with SnO2.

Kohn anomalies in superconductors

International Nuclear Information System (INIS)

Flatte, M.E.

1994-01-01

The detailed behavior of phonon dispersion curves near momenta which span the electronic Fermi sea in a superconductor is presented. An anomaly, similar to the metallic Kohn anomaly, exists in a superconductor's dispersion curves when the frequency of the photon spanning the Fermi sea exceeds twice the superconducting energy gap. This anomaly occurs at approximately the same momentum but is stronger than the normal-state Kohn anomaly. It also survives at finite temperature, unlike the metallic anomaly. Determination of Fermi-surface diameters from the location of these anomalies, therefore, may be more successful in the superconducting phase than in the normal state. However, the superconductor's anomaly fades rapidly with increased phonon frequency and becomes unobservable when the phonon frequency greatly exceeds the gap. This constraint makes these anomalies useful only in high-temperature superconductors such as La 1.85 Sr 0.15 CuO 4

Hard-Wired Dopant Networks and the Prediction of High Transition Temperatures in Ceramic Superconductors

International Nuclear Information System (INIS)

Phillips, J.C.

2010-01-01

The review multiple successes of the discrete hard-wired dopant network model ZZIP, and comment on the equally numerous failures of continuum models, in describing and predicting the properties of ceramic superconductors. The prediction of transition temperatures can be regarded in several ways, either as an exacting test of theory, or as a tool for identifying theoretical rules for defining new homology models. Popular first principle methods for predicting transition temperatures in conventional crystalline superconductors have failed for cuprate HTSC, as have parameterized models based on CuO2 planes (with or without apical oxygen). Following a path suggested by Bayesian probability, it was found that the glassy, self-organized dopant network percolative model is so successful that it defines a new homology class appropriate to ceramic superconductors. The reasons for this success in an exponentially complex (non-polynomial complete, NPC) problem are discussed, and a critical comparison is made with previous polynomial (PC) theories. The predictions are successful for the superfamily of all ceramics, including new non-cuprates based on FeAs in place of CuO2.

Raman spectra of Hg-based superconductors: Effect of oxygen defects

International Nuclear Information System (INIS)

Zhou, X.; Cardona, M.; Chu, C.W.; Lin, Q.M.; Loureiro, S.M.; Marezio, M.

1996-01-01

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa 2 Ca n-1 Cu n O 2n+2+δ (n=1, 2, 3, 4, and 5) high-T c superconductor family. A systematic evolution of the spectrum, which mainly involves oxygen-related phonons around 590, 570, 540, and 470 cm -1 , with an increasing number of CuO 2 layers, has been observed. Local laser annealing measurements clearly demonstrate that all these phonons are closely related to interstitial oxygen in the HgO δ planes. The origin of the spectrum evolution with the number of CuO 2 layers lies in the variation of interstitial oxygen content. copyright 1996 The American Physical Society

Labelled T{sub 3}, T{sub 4} and TBP for In Vitro Testing of Thyroid Function in Man and Animals

Energy Technology Data Exchange (ETDEWEB)

Czerniak, P.; Boruchowski, Sabina; Shomron, I. [Dept. of Radiotherapy and Isotopes, Tel-Hashomer Hospital, Tel-Aviv University Medical School, Faculty of Continuing Medical Education, Tel-Aviv (Israel)

1970-02-15

Iodothyronines are bound to determined electrophoretic fractions of serum proteins - TBP (TBG, TBA, TBPA). Radioiodine labelled T{sub 3} and T{sub 4} complex the free TBP fractions until saturation. The excess of added in vitro thyronines is then absorbed by the RBC. The changes described can be detected and quantitatively determined by radioisotope tests: radioelectrophoresis - T{sub 3/4} BP test, and RBC - {sup 125}I T{sub 3} test (Hamolsky test). The in vitro tests of the thyroid function can be clinically reliable if the protein fractions are normal, and they may be altered without thyroid pathology if the TBG fractions are abnormal. The electrophoretic fractions vary quantitatively and qualitatively in animals of different classes and orders. We chose these features to study the correlation between iodothyronines, plasma proteins and the above-mentioned thyroid tests. Twenty-two animal species (arranged according to the increasing percentage of the Hamolsky test) were examined: goat (8.6%, cow, lamb, calf, man, camel, goose, hamster, rat, turkey, marmot, duck, horse, donkey, hen, dog, pigeon, rabbit, guinea-pig, mouse, fish and frog (91.5%). The following additional parameters were examined: PBI, serum quantitative electrophoresis, T{sub 3} BP studies. All the tests were performed under identical technical conditions. Results and conclusions: (1) The Hamolsky test in the examined animals ranges from 9% to 92%. It is highest in the poicolothermics, in which much prealbumin and few glubulins are found on electrophoresis. The T{sub 3} BP is low, and about a half of the added {sup 125}I T{sub 3} remains unbound. (2) T{sub 3} and T{sub 4} are complexed with T{sub 3} BP and T{sub 4} BP fractions, which correspond to prealbumin, albumin, alpha 1-2, beta and exceptionally gamma globulin. The fractions are variable but characteristic for each animal species. T{sub 3} BP does not correlate exactly with T{sub 4} BP, and seems to be distributed over more fractions

Crystal Growth and Neutron Scattering Study of Spin Correlations of the T‧-Structured Pr2‑x Ca x CuO4

Science.gov (United States)

Fujita, Masaki; Tsutsumi, Kenji; Miura, Tomohiro; Danilkin, Sergey

2018-03-01

We studied Ca-doping effect on spin correlations in T‧-structured cuprate oxide RE2CuO4 (RE: rear earth) with growing a sizable single crystal of Pr2‑x Ca x CuO4 (x=0.05 and 0.10) as well as synthesizing powder samples of Pr1.90Ca0.10CuO4 and Eu1.90Ca0.10CuO4. In the all as-prepared and annealed samples, no evidence of shielding signal associated with superconductivity was observed by magnetic susceptibility measurement. Elastic neutron scattering measurements on the as-grown Pr1.90Ca0.10CuO4 clarified the existence of long-ranged magnetic order with commensurate spin correlation. The ordering temperature was determined to be ∼290K, which is comparable to Néel temperature in the parent compound of Pr2CuO4. The existence of commensurate low-energy spin excitation was also confirmed by inelastic neutron scattering measurements for the annealed Pr1.95Ca0.05CuO4. These results strongly suggest a negligible Ca-doping effect on the physical properties in T‧-RE2CuO4, which is quite different from the drastic doping evolution of magnetism in T -RE2CuO4.

Correlation mediated superconductivity in a 'High-Tsub(c)' model

International Nuclear Information System (INIS)

Long, M.W.

1987-08-01

A simple model is presented to account for the High-Tsub(c) perovskite superconductors. The superconducting mechanism is purely electronic and comes from local Hubbard correlations. The model comprises a Hubbard model for the copper sites with a single particle oxygen band between the two copper Hubbard bands. The electrons move only between nearest neighbour atoms which are of different types. Using two very different approximation schemes, one related to 'Slave-Boson' mean field theory and the other based on an exact local Fermion transformation, the possibility of copper-oxygen or a mixture of copper-oxygen and oxygen-oxygen pairing is shown. The author believes that the most promising situation for superconductivity is with the Oxygen band over half-filled and closer in energy to the lower Hubbard band. (author)

Tl Cuprate Superconductors Studied by XPS

International Nuclear Information System (INIS)

Vasquez, R. P.; Siegal, M. P.; Overmyer, D. L.; Ren, Z. F.; Lao, J. Y.; Wang, J. H.

1999-01-01

XPS measurements on epitaxial thin films of the Tl cuprate superconductors Tl2Ba2CaCu2O8, Tl2Ba2Ca2Cu3O10, and Tl0.78Bi0.22Ba0.4Sr1.6Ca2Cu3O9-δ are presented. These data, together with previous measurements in this lab on Tl2Ba2CuO6-δ and TlBa2CaCu2O7-δ, comprise a comprehensive data set for comparison of Tl cuprates in which the number of Tl-O and Cu-O layers, and hence the chemical and electronic properties, vary. (c) 2000 American Vacuum Society

Atomic resolution chemical bond analysis of oxygen in La2CuO4

Science.gov (United States)

Haruta, M.; Nagai, T.; Lugg, N. R.; Neish, M. J.; Nagao, M.; Kurashima, K.; Allen, L. J.; Mizoguchi, T.; Kimoto, K.

2013-08-01

The distorted CuO6 octahedron in La2CuO4 was studied using aberration-corrected scanning transmission electron microscopy at atomic resolution. The near-edge structure in the oxygen K-edge electron energy-loss spectrum was recorded as a function of the position of the electron probe. After background subtraction, the measured spectrum image was processed using a recently developed inversion process to remove the mixing of signals on the atomic columns due to elastic and thermal scattering. The spectra were then compared with first-principles band structure calculations based on the local-density approximation plus on-site Coulomb repulsion (LDA + U) approach. In this article, we describe in detail not only anisotropic chemical bonding of the oxygen 2p state with the Cu 3d state but also with the Cu 4p and La 5d/4f states. Furthermore, it was found that buckling of the CuO2 plane was also detectable at the atomic resolution oxygen K-edge. Lastly, it was found that the effects of core-hole in the O K-edge were strongly dependent on the nature of the local chemical bonding, in particular, whether it is ionic or covalent.

Josephson plasma resonance in vortex filament state of high temperature superconductors

International Nuclear Information System (INIS)

Matsuda, Yuji; Gaifullin, M.B.

1996-01-01

High temperature superconductors have the crystalline structure in which two-dimensional CuO 2 planes are piled in layers, consequently, the anisotropy of electroconductivity arises, and this brings about stable and low energy Josephson plasma in superconducting state. Also as to the vortex filament state of high temperature superconductors, the effect of thermal fluctuation due to low dimensionality, short coherence length and high transition temperature becomes conspicuous. In reality, these plasma and vortex filament state are related closely. Light reflection and plasma edge in superconducting state, Josephson plasma resonance in the vortex filament state of BiO 2 Sr 2 CaCu 2 O 8+δ , the plasma vibration in Josephson junction, Josephson plasma in magnetic field, Josephson plasma in the liquid state of vortex filament, Josephson plasma in the solid state of vortex filament, and Josephson plasma in parallel magnetic field are reported. The Josephson plasma resonance is the experimental means for exploring vortex filament state from microscopic standpoint, and its development hereafter is expected. (K.I.)

Dependence of Tc on the oxygen distribution in the Cu-O chains in the high temperature superconductors YBa2Cu3O6+x

International Nuclear Information System (INIS)

Uimin, G.V.; Gantmakher, V.F.; Neminsky, A.M.; Novomlinsky, L.A.; Shovkun, D.V.; Bruell, P.

1992-01-01

It is experimentally confirmed that in YBa 2 Cu 3 O 6+x ceramics with x fixed within the range 0.4-0.5 the temperature of the superconducting transition Tc can be appreciably reduced by quenching a sample from moderate temperatures between 50degC and 200degC. The theory developed for the description of the ensemble of Cu-O-... chain fragments in orthorhombic phase is applied for the explanation of the experimental results, which can be interpreted as follows. In ortho-II phase the oxygen filling factors in oxygen deficient Cu(1) planes alternate from row to row. Alternation decreases with temperature increasing. Redistribution of the oxygen ions between the rows increases the fraction of short Cu-O-... chain fragments which cannot inject holes into CuO 2 planes. This diminishes the hole concentration in the Cu(2) planes and, hence, Tc. Near 150degC the sample undergoes the second order transition into ortho-I phase where rows are equally filled with oxygen. Further increasing of the temperature does not reveal an appreciable reduction of Tc. A comparison of the experiment with the simplest model is performed. (orig.)

Superconducting specific heat jump Δ C ∝ T{sub c}{sup β} (β ∝ 2) and gapless Fermi surfaces in K{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Grinenko, V.; Efremov, D.V.; Drechsler, S.L.; Aswartham, S.; Gruner, D.; Roslova, M.; Morozov, I.; Nenkov, K.; Wolter, A.U.B. [Leibniz-Institute for Solid State and Materials Research, IFW-Dresden (Germany); Wurmehl, S.; Buechner, B. [Leibniz-Institute for Solid State and Materials Research, IFW-Dresden (Germany); Institut fuer Festkoerperphysik, TU Dresden (Germany); Holzapfel, B. [Leibniz-Institute for Solid State and Materials Research, IFW-Dresden (Germany); Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen (Germany)

2014-07-01

We present a systematic study of the electronic specific heat jump (Δ C{sub el}) at the superconducting transition temperature T{sub c} of K{sub 1-x}Na{sub x}Fe{sub 2}As{sub 2}. Both T{sub c} and Δ C{sub el} monotonously decrease with increasing x. The jump scales approximately with a novel power-law: Δ C{sub el} ∝ T{sub c}{sup β} with β ∼ 2 determined by the impurity scattering rate. This finding is in sharp contrast to most of all iron-pnictide superconductors with a cubic Bud'ko-Ni-Canfield (BNC) scaling. Our observations, also, suggests that disorder diminishes the small gaps leading to partial gapless superconductivity which results in a large residual Sommerfeld coefficient in the superconducting state for x > 0. Both T-dependence of C{sub el}(T) in the superconducting state and the nearly quadratic scaling of Δ C{sub el} at T{sub c} are well described by the Eliashberg-theory for a single-band d-wave superconductor with weak pair-breaking due to nonmagnetic impurities having reduced the density of superconducting quasi-particles.

Phase Equilibria Relationships of High-Tc Superconductors

International Nuclear Information System (INIS)

Wong-Ng, Winnie

2011-01-01

As an integral part of a R and D program partially supported by the Electricity Delivery and Energy Reliability Office of DOE, we have determined phase equilibria data and phase diagrams for the three generations of superconductor materials: 1st generation, (Bi,Pb)-Sr-Ca- Cu-O systems; 2nd generation, Ba-R-Cu-O systems (R=lanthanides and yttrium); and 3rd generation, MgB2 systems. Our studies involved bulk materials, single crystals and thin films. This report gives a summary of our accomplishments, a list of publications, and 15 selected journal publications.

Dynamic T{sub 2}-mapping during magnetic resonance guided high intensity focused ultrasound ablation of bone marrow

Energy Technology Data Exchange (ETDEWEB)

Waspe, Adam C.; Looi, Thomas; Mougenot, Charles; Amaral, Joao; Temple, Michael; Sivaloganathan, Siv; Drake, James M. [Centre for Image Guided Innovation and Therapeutic Intervention, The Hospital for Sick Children, Toronto, ON, M5G 1X8 (Canada); Philips Healthcare Canada, Markham, ON, L6C 2S3 (Canada); Centre for Image Guided Innovation and Therapeutic Intervention, The Hospital for Sick Children, Toronto, ON, M5G 1X8 (Canada); Department of Applied Mathematics, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada); Centre for Image Guided Innovation and Therapeutic Intervention, The Hospital for Sick Children, Toronto, ON, M5G 1X8 (Canada)

2012-11-28

Focal bone tumor treatments include amputation, limb-sparing surgical excision with bone reconstruction, and high-dose external-beam radiation therapy. Magnetic resonance guided high intensity focused ultrasound (MR-HIFU) is an effective non-invasive thermotherapy for palliative management of bone metastases pain. MR thermometry (MRT) measures the proton resonance frequency shift (PRFS) of water molecules and produces accurate (<1 Degree-Sign C) and dynamic (<5s) thermal maps in soft tissues. PRFS-MRT is ineffective in fatty tissues such as yellow bone marrow and, since accurate temperature measurements are required in the bone to ensure adequate thermal dose, MR-HIFU is not indicated for primary bone tumor treatments. Magnetic relaxation times are sensitive to lipid temperature and we hypothesize that bone marrow temperature can be determined accurately by measuring changes in T{sub 2}, since T{sub 2} increases linearly in fat during heating. T{sub 2}-mapping using dual echo times during a dynamic turbo spin-echo pulse sequence enabled rapid measurement of T{sub 2}. Calibration of T{sub 2}-based thermal maps involved heating the marrow in a bovine femur and simultaneously measuring T{sub 2} and temperature with a thermocouple. A positive T{sub 2} temperature dependence in bone marrow of 20 ms/ Degree-Sign C was observed. Dynamic T{sub 2}-mapping should enable accurate temperature monitoring during MR-HIFU treatment of bone marrow and shows promise for improving the safety and reducing the invasiveness of pediatric bone tumor treatments.

ESR of Gd3+ in magnetically ordered Eu2CuO4

International Nuclear Information System (INIS)

Rettori, C.; Oseroff, S.B.; Rao, D.; Valdivia, J.A.; Barberis, G.E.; Martins, G.B.; Sarrao, J.; Fisk, Z.; Tovar, M.

1996-01-01

Electron spin resonance (ESR) experiments of Gd 3+ in the antiferromagnetic (AF) ordered phase (T N ) of Eu 2 CuO 4 can be interpreted in terms of four magnetically nonequivalent rare-earth sites with local internal fields H i =±310(30) Oe along the [100] and [010] directions. The internal field is well described by a dipolar magnetic field of a noncollinear AF array of 0.35(4) μ B per Cu moment aligned along the [100] and [010] directions. This is consistent with recent results of magnetic-field-dependent neutron-diffraction experiments. From the ESR and magnetic susceptibility data, the crystal field parameters for Gd 3+ and Eu 3+ in Eu 2 CuO 4 are determined. The exchange parameters between the rare earths are also estimated. copyright 1996 The American Physical Society

High critical magnetic field superconductor La3S4

International Nuclear Information System (INIS)

Westerholt, K.; Bach, H.; Wendemuth, R.; Methfessel, S.

1979-01-01

A report is presented on electrical conductivity, specific heat and magnetization measurements on La 3 S 4 single crystals. The results show that La 3 S 4 is a strong coupling superconductor with a BCS coherence length of 132 A. This extremely low value makes La 3 S 4 an intrinsic high critical magnetic field superconductor with a Landau-Ginsburg parameter of 20. For the temperature gradient of the upper critical magnetic field at the transition temperature values are found up to 35 kG/K. (author)

Spectroscopic views of high-Tc superconductors

International Nuclear Information System (INIS)

Wendin, G.

1989-01-01

In this paper progress in the field of photoelectron spectroscopy, electron energy loss spectroscopy, inverse photoemission, and infrared- and optical reflectivity applied to high-T c superconductors in analyzed in terms of correlation effects, transport properties and Fermi liquid behavior. For the CuO 2 based materials, a picture emerges of localized holes in copper 3d levels and itinerant holes in oxygen 2p-like bands. A Fermi liquid picture and a superconducting gap is indicated by angle-resolved photoemission, infrared absorption, and NMR. A Fermi surface is indicated by positron annihilation. Infrared absorption revels strongly frequency and temperature dependent scattering and polaronic behavior for frequencies below 0.1 eV. Infrared absorption indicates a maximum superconducting gas of 2Δ/K B T c = 8 and suggests that ordinary samples may show a range of gaps 2 B T c B = 5

Gadolinium-enhanced T{sub 1}-weighted MR urography versus T{sub 2}-weighted (HASTE) MR urography in children; Kontrastangehobene T{sub 1}-gewichtete MR-Urographie versus T{sub 2}-gewichtete (HASTE) MR-Urographie im Kindesalter

Energy Technology Data Exchange (ETDEWEB)

Staatz, G.; Nolte-Ernsting, C.C.A.; Haage, P.; Tacke, J.; Guenther, R.W. [Technische Hochschule Aachen (Germany). Klinik fuer Radiologische Diagnostik; Rohrmann, D. [Technische Hochschule Aachen (Germany). Urologische Klinik; Stollbrink, C. [Technische Hochschule Aachen (Germany). Kinderklinik

2001-11-01

Purpose: To evaluate gadolinium-enhanced T{sub 1}-weighted excretory MR urography (EMRU) versus T{sub 2}-weighted (HASTE) MR urography in children with upper urinary tract abnormalities. Patients and Methods: In a prospective study 63 children, aged from 3 weeks to 15 years, underwent MR urography in a 1.5-T scanner. Before and after an intravenous injection of 0.05 mg/kg body weight of furosemide, respiratory-triggered HASTE images were obtained for T{sub 2}-weighted MR urography. EMRU was performed subsequent to i.v. gadolinium injection with respiratory-gated, coronal 3D-gradient-echo sequences. Results: Compared to T{sub 2}-weighted (HASTE) MR urography, gadolinium-enhanced MR urography revealed a superior diagnostic accuracy in non-dilated collecting systems (horseshoe kidneys, ectopic kidneys, duplex systems, single ectopic ureters, ureteroceles). EMRU and T{sub 2}-weighted (HASTE) MRU turned out to be equivalent in the assessment of obstructed but normal functioning upper urinary tracts (UPJ obstructions, megaureters). Non-functioning dilated collecting systems and multicystic dysplastic kidneys were best visualized with use of T{sub 2}-weighted (HASTE) MR urography. Conclusion: Respiratory-gated gadolinium-enhanced T{sub 1}-weighted MRU allows accurate evaluation of most upper urinary tract abnormalities. T{sub 2}-weighted (HASTE) MRU complements GMRU in the evaluation of non-functioning renal units and cystic disease of the kidneys. (orig.) [German] Ziel: Vergleich der kontrastangehobenen T{sub 1}-gewichteten MR-Urographie mit der T{sub 2}-gewichteten (HASTE) MR-Urographie bei Kindern mit Anomalien des oberen Harntraktes. Methoden: In einer prospektiven Studie wurde bei 63 Kindern (3 Wo. - 15J.) eine MR-Urographie (MRU) in einem 1,5-Tesla-Magneten durchgefuehrt. Die T{sub 2}-gewichtete MRU erfolgte vor und nach intravenoeser Injektion von 0,05 mg/kg KG Furosemid mit atemgetriggerten HASTE-Sequenzen. Fuer die T{sub 1}-gewichtete MRU wurden nach

Evidence for monoclinic distortion in the ground state phase of underdoped La_1_._9_5Sr_0_._0_5CuO_4: A single crystal neutron diffraction study

International Nuclear Information System (INIS)

Singh, Anar; Schefer, Jürg; Frontzek, Matthias; Sura, Ravi; Conder, Kazimierz; Sibille, Romain F.; Ceretti, Monica; Paulus, Werner

2016-01-01

The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La_1_._9_5Sr_0_._0_5CuO_4 has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for “forbidden” reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La_1_._9_5Sr_0_._0_5CuO_4 at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in a continuous way; however, the structure is stable below ∼120 K which agrees with other observed phenomena. Our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.

Electron energy-loss spectroscopy on n-type doped high-temperature superconductors and related systems

International Nuclear Information System (INIS)

Alexander, M.

1992-08-01

Electron-enery loss spectroscopy measurements on n-type doped high temperature superconductors, their undoped parent compounds, Y-doped Bi 2 Sr 2 CaCu 2 O 8 and some rare earth oxides are presented. The undoped parent compounds Ln 2 CuO 4 (Ln = Pr, Nd, Sm) are charge transfer insulators with a charge transfer energy gap of 1.4 eV. The conduction band lies in the CuO 2 plane and has mainly Cu3d x 2 -y 2 character. O2p x,y states are slightly hybridized with this band. Upon partially substituting the trivalent Ln ions by tetravalent Ce or Th and monovalent F for the O ions, electron doping of the CuO 2 plane occurs with the electrons having mainly Cu3d character. A rigid band behaviour is proposed by several band structure calculations could be ruled out, as well as the occurence of so called 'mid-gap' states appearing inside the band gap between the valence and conduction bands. The position of the Fermi level was found to be at the bottom of the conduction bands. No measurable influence of the reduction process, necessary to obtain superconductivity, was detected in the unoccupied density of states. Characteristics shifts of the measured oxygen and copper edges were correlated with crossing the metal-insulator transition. These shifts are most probably caused by an improved screening capacity of the free charge carriers. A similar effect was also observed in Y-doped Bi 2 Sr 2 CaCu 2 O 8 . Thus, it was possible to show that the disappearance of the valence band hole states upon doping did not occur in a rigid-band-like manner. The low energy excitations in Nd 1.85 Ce 0.15 CuO 4-δ showed a plasmon like excitation at about 1 eV as well as a reduction and an energy shift of the charge transfer excitation. The dispersion of this plasmon excitation was determined. (orig.)

Muon and neutron investigations of vortex correlations in high-Tc superconductors

International Nuclear Information System (INIS)

Aeppli, G.

1991-01-01

The muon spin relaxation (μSR) and neutron scattering techniques have made the following contributions to the author's understanding of copper oxide superconductors: (1) determination in absolute units of the magnetic length λ(T); (2) observation in YBa 2 Cu 3 O 7 of well ordered flux lattices, composed of straight flux lines, at low T and intermediate fields; (3) demonstration that sample multiphase coexistence is the most likely cause of reduced Meissner fractions found for La 2-x Sr x CuO 4 ceramics with non-optimal (i.e. x ≠ 0.15); (4) finding that microscopic irreversibility sets in at surprisingly low T; (5) observation of microscopic vortex motion in BiSrCaCuO single crystals. While studies of type (1) have been extensively performed, there have been relatively few experiments of the other four varieties. Therefore, he concludes that both μSR and neutron diffraction still have the potential to provide new information about the magnetic correlations in high-T c materials

Magnetic tri-axial orientation in (Y1-xErx)2Ba4Cu7O15-y superconductors

International Nuclear Information System (INIS)

Horii, S.; Okuhira, S.; Yamaki, M.; Haruta, M.; Maeda, T.; Shimoyama, J.

2011-01-01

(Y 1-x Er x ) 2 Ba 4 Cu 7 O 15-y [(Y,Er)247] was synthesized for clarifying a magnetic role of Er ion. The three magnetization axes of (Y,Er)247 were obtained from tri-axial orientation using a modulated rotation magnetic field. Magnetic anisotropy of Er ion is roughly ten times higher than that for Y247 at room temperature. Importance of rare-earth ions was shown for reduction of required magnetic fields in the tri-axial magnetic orientation. We report the tri-axial grain-orientation effects under a modulated rotation magnetic field for (Y 1-x Er x ) 2 Ba 4 Cu 7 O y [(Y, Er)247]. The magnetic easy axis at room temperature was drastically changed around x ∼ 0.1; however, the Er-doping levels for the conversion of magnetic easy axes from the c-axis to the ab-direction and from the a- to b-axes were quite different. Tri-axial single-ion magnetic anisotropy of Er 3+ was roughly 10 times greater than tri-axial magnetic anisotropy generated by both the superconducting CuO 2 plane and the blocking Cu-O chain layer. An appropriate choice of rare-earth (RE) ions in RE-based cuprate superconductors enables the reduction of the required magnetic field for the production of bulks and thick films based on the magnetic orientation technique.

Raman study of HgBa 2Ca n-1 Cu nO 2 n+2+ δ ( n=1,2,3,4 and 5) superconductors

Science.gov (United States)

Zhou, Xingjiang; Cardona, M.; Chu, C. W.; Lin, Q. M.; Loureiro, S. M.; Marezio, M.

1996-02-01

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa 2Ca n-1 Cu nO 2 n+2+ δ ( n=1,2,3,4 and 5) high- Tc superconductor family using different laser frequencies. Local laser annealing measurements were carried out to investigate the variation of the Raman spectra with the excess oxygen content, δ. A systematic evolution of the spectra, which display mainly peaks near 590, 570, 540 and 470 cm -1, with increasing number of CuO 2 layers has been observed; its origin has been shown to lie in the variation of the interstitial oxygen content. In addition to confirming that the 590 cm -1 mode represents vibration of apical oxygens in the absence of neighboring excess oxygen, the 570 cm -1 mode, which may be composed of some finer structures, has been assigned to the vibration of the apical oxygen modified by the presence of the neighboring excess oxygens. The 540 and 470 cm -1 modes may represent the direct vibration of excess oxygens. The implication of possible different distribution sites of excess oxygens is discussed. All other observed lower-frequency modes are also assigned.

Critical current density of four-CuO2-layer T1Ba2Ca3Cu4O11-δ

International Nuclear Information System (INIS)

Zhang, L.; Liu, J.Z.; Shelton, R.N.

1998-01-01

Full text: A key requirement for technological application is to have superconductors with high critical current density at practical operating temperatures and magnetic fields. The critical current density is strongly related to underlying properties of high T c superconductors, such as layering, anisotropy and other intrinsic material structures. The thallium-based superconductors attracted much attention at early stage mainly due to their high superconducting transitions. Recent studies show that these materials appear to be a better choice for achieving higher critical current density because of a stronger interlayer coupling between superconducting layers. Single crystals of TlBa 2 Ca 3 Cu 4 O 11-δ were grown by a self-flux method. This material is a strong-layered superconductor with four-CuO 2 -planes in a unit cell and a superconducting transition temperature of 128K. Our experimental results show that TlBa 2 Ca 3 Cu 4 O 11-δ crystals have high irreversibility line, large critical current density and high upper critical field. The impact of layering and the number of Cu-O layers on flux pinning, critical current density and other magnetic properties will also be discussed

Geometric distribution of CuO chains in YBa2Cu3O6+x

International Nuclear Information System (INIS)

Matic, V.M.; Lazarov, N.Dj.

2006-01-01

Statistics of CuO chains in basal planes of YBa 2 Cu 3 O 6+x high-T c superconductor has been studied in terms of two dimensional asymmetric next-to-nearest-neighbor Ising (ASYNNNI) model, with accentuation on distribution of CuO chains per different chain lengths. It has been shown that the fraction p(l) of CuO chains containing l oxygen ions (i.e., having the length equal to l), satisfies so-called ''law of geometric distribution''p(l)=ω(1-ω) l-1 , where the quantity ω is equal to the inverse of average chain length l av in the system, for given values of oxygen content x and temperature T. In the case of ortho-II (OII) structural phase, the geometric chain probability distribution is shown to hold separately for each of two different sublattices of oxygen sites, commonly known as α 1 and α 2 , with respectively defined l av α 1 (x,T) and l av α 2 (x,T). The theoretically derived result of the chain probability distribution p(l) is shown to be in a remarkable agreement with the results obtained out of extensive Monte Carlo calculations that were made within region of stability of orthorhombic structural phases in (x,T) space. The relevance of chain length distribution for accurate count of the number of transferred electronic holes to superconducting CuO 2 layers has been pointed out and expression for hole concentration has been derived. The concept of critical chain length for charge transfer mechanism was briefly discussed

Transport Measurements on NEODYMIUM(1.85) CERIUM(.15) Copper OXYGEN(4-DELTA) Thin Films

Science.gov (United States)

Kussmaul, Andreas

1992-01-01

This work describes the synthesis and the study of the transport properties of thin films of Nd _{1.85}Ce_{.15 }CuO_{4-delta} carried out respectively at the IBM T. J. Watson Research Center in collaboration with Dr. A. Gupta, and at the Francis Bitter National Magnet Laboratory under the direction of Dr. P. M. Tedrow. The thin films were prepared by laser ablation of a stoichiometric target on heated substrates in a reactive ambient. The influence of the deposition parameters was studied, and the use of a nitreous oxide ambient was found to yield a clear improvement of the sample quality. The transport properties of the films were measured at low temperatures and in high magnetic fields. Non superconducting samples showed a strong, highly anisotropic, negative magnetoresistance that is consistent with two dimensional weak-localization. Superconducting samples show two dimensional fluctuation effects above T_{c}. The theory of fluctuations in a magnetic field was used to extract the position of H_{c2} (in the perpendicular direction) in the broad and almost featureless resistive transition, and the extracted values were fit to the theory of dirty superconductors. The angular dependence of the resistive transition was studied close to T _{c} and found to be somewhat better described by a two-dimensional model. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

Extraordinary superconductor with nearly trivalent cerium, CeCu2Si2

International Nuclear Information System (INIS)

Ishikawa, M.; Jaccard, D.; Jorda, J.-L.

1982-01-01

Concentrating on the ternary phase diagram, the authors have performed a complementary investigation on CeCu 2 Si 2 and confirm that the compound containing nearly trivalent cerium ions is a new type of superconductor with Tsub(c) around 0.5 K. The analyses of the upper critical field curve support the description of the compound by heavy fermion quasiparticles. Other particular features of this compound are also presented. (Auth.)

Serum levels of triiodothyronine (T{sub 3}) and thyroxine (T{sub 4}) in buffalo (Bubalus bubalis Lin.) raised in Amazon region; Niveis sericos de triiodotironina (T{sub 3}) e tiroxina (T{sub 4}) em bubalinos (Bubalus bubalis Lin.) criados na regiao Amazonica

Energy Technology Data Exchange (ETDEWEB)

Silva, A O.A. da

1991-08-01

Through the use of radioimmunoassay (RIA) it was determined blood serum concentration of triiodothyronine (T{sub 3}) and thyroxine (T{sub 4}) (n=78) for two different water buffalo racial groups. Blood serum was collected from young and adult animals belonging to two farms in Castanhal country, state of Para, Brazil, through the year of 1988. The serum levels of T{sub 3} and T{sub 4} were statistically correlated with climatic parameters, e.g., pluviometric precipitation, environmental temperature, humidity, light intensity variation and physiological factors such as age, breed and sex. It was identified two seasons during experiment, one season the rainfall period with high precipitation rates and the other one was considered as dry season, with low precipitation rates. The average rate of temperature and humidity have shown no significant statistic difference between the two seasons. On the other hand, it was found a significant relationship between luminosity and seasons, since when the luminosity decreases the pluviometric rates increases. (author). 51 refs, 15 figs, 15 tabs.

(Bi, Pb).sub.2, Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x superconductor and method of making same utilizing sinter-forging

Science.gov (United States)

Chen, Nan; Goretta, Kenneth C.; Lanagan, Michael T.

1998-01-01

A (BiPb).sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x (Bi223) superconductor with high J.sub.c, phase purity, density and mechanical strength is formed from Bi2223 powder which is synthesized from a mixture of Bi.sub.2 O.sub.3, PbO, SrCO.sub.3, CaCo.sub.3 and CuO. The mixture is milled, then dried and calcined to synthesize the Bi2223 powder with the desired phase purity. The calcination is performed by heating the dried mixture for 50 hours at 840.degree. C. The partially synthesized powder is then milled for 1-4 hours before calcining further for another 50 hours at 855.degree. C. to complete the synthesis. After calcination, the Bi2223 powder is cold pressed to a predetermined density and sinter forged under controlled temperature and time to form a Bi2223 superconductor with the desired superconducting properties.

(Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconductor and method of making same utilizing sinter-forging

Science.gov (United States)

Chen, N.; Goretta, K.C.; Lanagan, M.T.

1998-10-13

A (BiPb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}(Bi223) superconductor with high J{sub c}, phase purity, density and mechanical strength is formed from Bi2223 powder which is synthesized from a mixture of Bi{sub 2}O{sub 3}, PbO, SrCO{sub 3}, CaCo{sub 3} and CuO. The mixture is milled, then dried and calcined to synthesize the Bi2223 powder with the desired phase purity. The calcination is performed by heating the dried mixture for 50 hours at 840 C. The partially synthesized powder is then milled for 1--4 hours before calcining further for another 50 hours at 855 C to complete the synthesis. After calcination, the Bi2223 powder is cold pressed to a predetermined density and sinter forged under controlled temperature and time to form a Bi2223 superconductor with the desired superconducting properties. 5 figs.

Distribution of flux-pinning energies in YBa2Cu3O(7-delta) and Bi2Sr2CaCu2O(8+delta) from flux noise

Science.gov (United States)

Ferrari, M. J.; Johnson, Mark; Wellstood, Frederick C.; Clarke, John; Mitzi, D.

1990-01-01

The spectral density of the magnetic flux noise measured in high-temperature superconductors in low magnetic fields scales approximately as the inverse of the frequency and increases with temperature. The temperature and frequency dependence of the noise are used to determine the pinning energies of individual flux vortices in thermal equilibrium. The distribution of pinning energies below 0.1 eV in YBa(2)Cu(3)O(7-delta) and near 0.2 eV in Bi(2)Sr(2)CaCu(2)O(8+delta). The noise power is proportional to the ambient magnetic field, indicating that the vortex motion is uncorrelated.

Positron-annihilation studies on the YBa2Cu4O8 superconductor

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.; Jean, Y.C.; Hor, P.H.; Meng, R.L.; Xue, Y.Y.; Huang, Z.J.; Chu, C.W.

1990-01-01

Positron-lifetime and Doppler-broadened annihilation-radiation line-shape parameter S in YBa 2 Cu 4 O 8 are observed to decrease with temperature below T c . The calculation of the positron-density distribution shows that the maximum of the positron density is in the region between the Cu-O double chains. The correlation between the temperature dependence of annihilation parameters and the positron-density distribution is discussed. The decrease in annihilation parameters below T c is understood in terms of a local electron transfer from the CuO 2 layers to the Cu-O chains in the superconducting state

Preparation of quality control samples for its use in the radioimmunoassay de T{sub 3}, T{sub 4} and TSH; Preparacion de muestras de control de calidad para su uso en el radioinmunoanalisis de T{sub 3}, T{sub 4} y TSH

Energy Technology Data Exchange (ETDEWEB)

Lavalley E, C; Delgado S, B; Ruiz J, A; Zambrano A, F

1991-09-15

The use of quality control samples is necessary to evaluate, in a very simple way, the quality of the assays in the radioimmunoanalysis, since allows to settle down a quality control intra and inter analysis. In this work the methodology used for the preparation of these samples with low, media and high concentration for hormones related with the thyroid is shown, being obtained the following concentrations: 50, 200 and 500 ng/dl for T{sub 3}; 5.6, 7.8 and 14.4 {mu} g/dl for T{sub 4} and 5.4, 13.4 and >50 {mu} U I/ml for TSH. (Author)

X-ray absorption spectroscopy on high-temperature superconductors and related compounds

International Nuclear Information System (INIS)

Pellegrin, E.J.H.A.

1995-07-01

The electronic structure of the cuprate high-temperature superconductors La 2-x Sr x CuO 4+δ , Tl 2 Ba 2 CaCu 2 O 8 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 has been investigated using polarization-dependent near-edge X-ray absorption fine structure spectroscopy (NEXAFS). In addition, La 2-x Sr x NiO 4+δ has been included in the actual study as an isostructural analogue to the La 2-x Sr x CuO 4+δ system. It appears that the electronic structure of these compounds corresponds to that of a p-type doped charge-transfer insulator including electron-electron interactions on the Cu(Ni) sites and a strong hybridization between Cu(Ni) and O atoms. It is concluded that the low-energy excitations in these compounds can be described on the basis of an effective one-band Mott-Hubbard model. The polarization-dependence of the above spectra gives evidence for the strong in-plane character of the intrinsic and the doped holes. The small amount and the doping-dependence of the out-of-plane character of these charge carriers rule out models for a microscopic mechanism of superconductivity based on a large amount of hole states in the corresponding Apex-O2p z /Cu3d 3z 2 -r 2 orbitals. On the other hand, the reduction of this anisotropy in the overdoped compounds together with similar findings in the macroscopic properties seems to indicate a detrimental influence of non-planar orbitals on the superconducting properties. The differences in the energetic ordering and atomic character of the states close to the Fermi level between the undoped compounds La 2 CuO 4+δ , La 2 NiO 4+δ , and NiO have been determined from the NEXAFS data. It is found that these differences can be explained by the different size of the tetragonal crystal field splitting E Z compared to that of the Hund's rule interaction J H in these systems. This gives evidence for the high-spin d 8 ground state of the undoped nickelates (i.e. J H >E Z ). It is suggested that the polarons in La 2-x Sr x NiO 4+δ can be seen as non

Comparison of internal friction in high Tc superconductors and CuO

International Nuclear Information System (INIS)

Gzowski, O.; Davoli, I.; Stizza, S.; Mancini, G.; Kusz, B.; Barczynski, R.; Gazda, M.; Sadowski, W.; Murawski, L.

1990-01-01

This paper reports on the internal friction and shielding effect in CuO, superconducting yttrium and bismuth ceramics and yttrium monocrystal that have been measured. Several features, some of them common for all specimens, have been found

Photocatalytic generation of hydrogen under visible light on La2CuO4

Indian Academy of Sciences (India)

Laboratory of Storage and Valorization of Renewable Energies, Faculty of Chemistry (USTHB),. B.P. 32, 16111 ... The energy diagram shows the feasibility of La2CuO4 for the H2 evolution under visible light. The best ... An efficient photocata-.

Positron annihilation studies on high temperature superconductors

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.

1996-01-01

A survey of the positron annihilation studies on high temperature superconductors (HTSC), with results drawn mainly from our work, is presented. These include results of the studies on the temperature dependence of positron lifetime across T c , which have been carried out in the whole gamut of oxide superconductors. These experimental results are discussed in conjunction with the results of theoretically calculated positron density distribution, and it is shown that the observed temperature dependence of lifetime is intimately linked to the probing of the Cu-O network by the positrons. Results on the investigation of oxygen defects, which play a crucial role in HTSC, are presented. The most significant contribution of positrons to HTSC relates to the investigation of Fermi surface and the results of these studies, drawn from literature, are indicated. Some of our recent results in other novel superconducting materials, viz., the fullerenes and borocarbides are also presented. (author). 69 refs., 15 figs

NMR/NQR study of the superconductor Y2Ba4Cu7O15

International Nuclear Information System (INIS)

Stern, R.

1995-01-01

This dissertation concentrates on several important aspects of the high temperature superconductivity research. Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies in Y-Ba-O compounds contribute information regarding various aspects, ranging from the direct observation of strong coupling between the adjacent planes in the double plane to conclusions concerning the spatial symmetry of paring state in these cuprates. We report the first results in the 93 K superconductor Y 2 Ba 4 Cu 7 O 15 . This compound turns out to be a structure containing differently doped CuO 2 planes. The planes in the 1-2-3(1-2-4) block are only slightly lower (higher) doped than those in the corresponding parent compounds YBa 2 Cu 3 O 7 and YBa 2 Cu 4 O 8 . The results obtained from measurements on oxygen depleted Y 2 Ba 4 Cu 7 O 15-x show two new features which could explain the dissimilar variation of T c with oxygen content compared to YBa 2 Cu 3 O 7-x : i) the double chains donate charge carriers to the planes and ii) the chain fragments which survive when emptying single chains are longer than in YBa 2 Cu 3 O 7-x . The pressure induced charge transfer from chain to plane in each block of Y 2 Ba 4 Cu 7 O 15 is the same as in the corresponding parent compound. We explore the strong coupling between nonequivalent planes in this compound using the three main NMR/NQR quantities, K spin , 1/T 1 ; and T 2G,ind , and estimate its approximate strength directly from spin-echo double resonance (SEDOR) experiments. We obtain for the ratio of the effective inter- and intraplane exchange-coupling constants the value of 0.3 just above T c . This ratio decreases with increasing temperature. (author) figs., tabs., refs

Electronic structure studies of La2CuO4

International Nuclear Information System (INIS)

Wachs, A.L.; Turchi, P.E.A.; Jean, Y.C.

1988-01-01

We report results of positron-electron momentum-distribution measurements of single-crystal La 2 CuO 4 using two-dimensional angular correlation of positron-annihilation-radiation techniques. The data contain two components: a large (∼85%), isotropic corelike electron contribution and a remaining, anisotropic valence-electron contribution modeled using a linear combination of atomic orbitals--molecular orbital method and a localized ion scheme, within the independent-particle model approximation. This work suggests a ligand-field Hamiltonian to be justified for describing the electronic properties of perovskite materials

Electronic structure studies of La2CuO4

Science.gov (United States)

Wachs, A. L.; Turchi, P. E. A.; Jean, Y. C.; Wetzler, K. H.; Howell, R. H.; Fluss, M. J.; Harshman, D. R.; Remeika, J. P.; Cooper, A. S.; Fleming, R. M.

1988-07-01

We report results of positron-electron momentum-distribution measurements of single-crystal La2CuO4 using two-dimensional angular correlation of positron-annihilation-radiation techniques. The data contain two components: a large (~85%), isotropic corelike electron contribution and a remaining, anisotropic valence-electron contribution modeled using a linear combination of atomic orbitals-molecular orbital method and a localized ion scheme, within the independent-particle model approximation. This work suggests a ligand-field Hamiltonian to be justified for describing the electronic properties of perovskite materials.

Anomalous magnetoresistance in the spinel superconductor LiTi2O4.

Science.gov (United States)

Jin, K; He, G; Zhang, X; Maruyama, S; Yasui, S; Suchoski, R; Shin, J; Jiang, Y; Yu, H S; Yuan, J; Shan, L; Kusmartsev, F V; Greene, R L; Takeuchi, I

2015-05-20

LiTi2O4 is a unique compound in that it is the only known spinel oxide superconductor. The lack of high quality single crystals has thus far prevented systematic investigations of its transport properties. Here we report a careful study of transport and tunnelling spectroscopy in epitaxial LiTi2O4 thin films. An unusual magnetoresistance is observed which changes from nearly isotropic negative to prominently anisotropic positive as the temperature is decreased. We present evidence that shows that the negative magnetoresistance likely stems from the suppression of local spin fluctuations or spin-orbit scattering centres. The positive magnetoresistance suggests the presence of an orbital-related state, also supported by the fact that the superconducting energy gap decreases as a quadratic function of magnetic field. These observations indicate that the spin-orbital fluctuations play an important role in LiTi2O4 in a manner similar to high-temperature superconductors.

Microscopic unravelling of nano-carbon doping in MgB{sub 2} superconductors fabricated by diffusion method

Energy Technology Data Exchange (ETDEWEB)

Wong, D.C.K. [School of Physics, The University of Sydney, New South Wales 2006 (Australia); Yeoh, W.K. [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, New South Wales 2006 (Australia); Australian Centre for Microscopy & Microanalysis, The University of Sydney, New South Wales 2006 (Australia); De Silva, K.S.B. [Institute for Superconducting & Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Institute for Nanoscale Technology, Faculty of Science, University of Technology Sydney, Ultimo, New South Wales 2007 (Australia); Kondyurin, A.; Bao, P. [School of Physics, The University of Sydney, New South Wales 2006 (Australia); Li, W.X. [School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China); Xu, X.; Peleckis, G.; Dou, S.X. [Institute for Superconducting & Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Ringer, S.P. [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, New South Wales 2006 (Australia); Australian Centre for Microscopy & Microanalysis, The University of Sydney, New South Wales 2006 (Australia); Zheng, R.K., E-mail: rongkun.zheng@sydney.edu.au [School of Physics, The University of Sydney, New South Wales 2006 (Australia)

2015-09-25

Highlights: • First report on nano-carbon doped MgB{sub 2} superconductors synthesized by diffusion method. • Microstructure and superconducting properties of the superconductors are discussed. • B{sub 4}C region blocks the Mg from reacting with B in the 10% nano-carbon doped sample. • MgB{sub 2} with 2.5% nano-carbon doped showed the highest J{sub c}, ≈10{sup 4} A/cm{sup 2} for 20 K at 4 T. - Abstract: We investigated the effects of nano-carbon doping as the intrinsic (B-site nano-carbon substitution) and extrinsic (nano-carbon derivatives) pinning by diffusion method. The contraction of the in-plane lattice confirmed the presence of disorder in boron sublattice caused by carbon substitution. The increasing value in full width half maximum (FWHM) in the X-ray diffraction (XRD) patterns with each increment in the doping level reveal smaller grains and imperfect MgB{sub 2} crystalline. The strain increased across the doping level due to the carbon substitution in the MgB{sub 2} matrix. The broadening of the T{sub c} curves from low to high doping showed suppression of the connectivity of the bulk samples with progressive dirtying. At high doping, the presence of B{sub 4}C region blocked the Mg from reacting with crystalline B thus hampering the formation of MgB{sub 2}. Furthermore, the unreacted Mg acted as a current blocking phase in lowering down the grain connectivity hence depressing the J{sub c} of the 10% nano-carbon doped MgB{sub 2} bulk superconductor.

High-resolution T{sub 2}-weighted cervical cancer imaging: a feasibility study on ultra-high-field 7.0-T MRI with an endorectal monopole antenna

Energy Technology Data Exchange (ETDEWEB)

Hoogendam, Jacob P.; Verheijen, Rene H.M.; Zweemer, Ronald P. [University Medical Centre Utrecht, Department of Gynaecological Oncology, UMC Utrecht Cancer Centre, PO Box 85500, Utrecht (Netherlands); Kalleveen, Irene M.L.; Castro, Catalina S.A. de; Raaijmakers, Alexander J.E.; Bosch, Maurice A.A.J. van den; Klomp, Dennis W.J.; Veldhuis, Wouter B. [University Medical Centre Utrecht, Department of Radiology, Utrecht (Netherlands)

2017-03-15

We studied the feasibility of high-resolution T{sub 2}-weighted cervical cancer imaging on an ultra-high-field 7.0-T magnetic resonance imaging (MRI) system using an endorectal antenna of 4.7-mm thickness. A feasibility study on 20 stage IB1-IIB cervical cancer patients was conducted. All underwent pre-treatment 1.5-T MRI. At 7.0-T MRI, an external transmit/receive array with seven dipole antennae and a single endorectal monopole receive antenna were used. Discomfort levels were assessed. Following individualised phase-based B{sub 1} {sup +} shimming, T{sub 2}-weighted turbo spin echo sequences were completed. Patients had stage IB1 (n = 9), IB2 (n = 4), IIA1 (n = 1) or IIB (n = 6) cervical cancer. Discomfort (ten-point scale) was minimal at placement and removal of the endorectal antenna with a median score of 1 (range, 0-5) and 0 (range, 0-2) respectively. Its use did not result in adverse events or pre-term session discontinuation. To demonstrate feasibility, T{sub 2}-weighted acquisitions from 7.0-T MRI are presented in comparison to 1.5-T MRI. Artefacts on 7.0-T MRI were due to motion, locally destructive B{sub 1} interference, excessive B{sub 1} under the external antennae and SENSE reconstruction. High-resolution T{sub 2}-weighted 7.0-T MRI of stage IB1-IIB cervical cancer is feasible. The addition of an endorectal antenna is well tolerated by patients. (orig.)

Three-dimensional superconductivity and vortex glass transition in La1.87Y0.13CuO4

International Nuclear Information System (INIS)

Lee, Hyun-Sook; Kim, Heon-Jung; Kim, Hyun-Jung; Jung, Myung-Hwa; Jo, Younghun; Lee, Sung-Ik; Tsukada, Akio; Naito, Michio

2006-01-01

The angular dependence of the critical current density (J c (θ)) and the vortex glass transition temperature (T g (θ)) in La 1.87 Y 0.13 CuO 4 were measured at different fields and temperatures. Both J c (θ) and T g (θ) showed a strong angular variation, which is typical for anisotropic superconductors. The angular variation could be described by using the anisotropic three-dimensional Ginzburg-Landau theory. From our analysis, we were able to estimate the anisotropy ratio

New Developments in the Theory of HTSC [High Temperature Superconductors

Science.gov (United States)

Abrikosov, A.A.

1994-09-01

The superconductor is supposed to consist of alternating layers of two kinds: (1) layers with an attractive electron interaction and an effective mass of usual magnitude, (2) layers without interaction and with a large effective mass. The overlap between the layers is assumed to be small, its energy, t, being much less than {Delta}. It is shown, that such a model explains the most peculiar property found in experiments on electronic Raman light scattering in BSCCO 2212: different threshold values for the Raman satellite measured at two different polarizations of the incident and scattered light. The tunneling conductance G(V)= dJ/dV is analyzed for the same model. In order to fit the qualitative features of experimental data, it is assumed that the tunneling probability to the normal layers is much less, than to the superconducting layers. The conductance is calculated for the case t{much_lt}{Delta}. A brief analysis is given for the case t{approximately}{Delta}, which proves that such an assumption definitely contradicts the experimental data for BSCCO. The possible nature of the electronic states in the normal layers is discussed. In connection with the experimental discovery (angle resolved photoemission spectroscopy, ARPES) of the extended saddle point singularities in the electron spectrum of a variety of HTSC consequences are derived for T{sub c} and {Delta} in a simple model. A large enhancement of superconductivity is possible if the singularity has a sufficient extension and is located close to the Fermi energy. In order to explain the anisotropy of the energy gap, observed in ARPES experiments, on the basis of the "extended saddle point singularities" an assumption is done that the Coulomb interactions are weakly screened, i.e. the Debye screening radius is much larger than the lattice period; this makes the electron interaction long ranged (E-L model).

Electron-$\\gamma$ - perturbed angular correlation studies on high-T$_{C}$ superconductors

CERN Document Server

Correia, J G; Marques, J G; Ramos, A R; Lourenço, A A; Amaral, V S; Galindo, V; Senateur, J P; Weiss, F; Wahl, U; Melo, A A; Soares, J C; Sousa, J B

2000-01-01

Recent results on the study of high-T$_{c}$ superconductors using the e$^-\\!-\\gamma$ perturbed angular correlation technique are presented. The basic features of the experimental equipment and its installation at the ISOLDE facility are briefly described. Results obtained from $^{197m}$Hg implanted into high quality Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{6+\\delta}$ epitaxy thin films are presented and discussed.

Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214

International Nuclear Information System (INIS)

Yung Moo Huh

2001-01-01

Thermodynamics has been studied systematically for the high temperature cuprate superconductor La 2-x Sr x CuO 4-δ , La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H(parallel)c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below T c , magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range from 0.060 (strongly underdoped) to 0.234 (strongly overdoped), the free energy change goes through a maximum at the optimum doped in a manner similar to the T c0 vs. x curve. The density of states, N(0), remains nearly constant in the overdoped and optimum doped regimes, taking a broad maximum around x = 0.188, and then drops abruptly towards zero in the underdoped regime. The La 2-x Sr x CuO 4 (La-214) system displays the fluctuating vortex behavior with the characteristic of either 2D or 3D fluctuations as indicated by clearly identifiable crossing points T* close to T c . The dimensional character of the fluctuations depends on both applied magnetic fields and the density of charge carriers. The dimensional crossover from 2D to 3D occurs in the strongly underdoped regime when the c-axis coherence distance ζ c becomes comparable to the spacing between adjacent CuO 2 layers s at sufficiently high magnetic fields near H c2

Thermodynamic Critical Field and Superconducting Fluctuation of Vortices for High Temperature Cuprate Superconductor: La-214

International Nuclear Information System (INIS)

Finnemore, Douglas K.

2001-01-01

Thermodynamics has been studied systematically for the high temperature cuprate superconductor La 2-x Sr x CuO 4-δ , La-214, in the entire superconductive region from strongly underdoped to strongly overdoped regimes. Magnetization studies with H (parallel) c have been made in order to investigate the changes in free energy of the system as the number of carriers is reduced. Above the superconducting transition temperature, the normal-state magnetization exhibits a two-dimensional Heisenberg antiferromagnetic behavior. Below T c , magnetization data are thermodynamically reversible over large portions of the H-T plane, so the free energy is well defined in these regions. As the Sr concentration is varied over the wide range from 0.060 (strongly underdoped) to 0.234 (strongly overdoped), the free energy change goes through a maximum at the optimum doped in a manner similar to the T c0 vs. x curve. The density of states, N(0), remains nearly constant in the overdoped and optimum doped regimes, taking a broad maximum around x = 0.188, and then drops abruptly towards zero in the underdoped regime. The La 2-x Sr x CuO 4 (La-214) system displays the fluctuating vortex behavior with the characteristic of either 2D or 3D fluctuations as indicated by clearly identifiable crossing points T* close to T c . The dimensional character of the fluctuations depends on both applied magnetic fields and the density of charge carriers. The dimensional crossover from 2D to 3D occurs in the strongly underdoped regime when the c-axis coherence distance ξ c becomes comparable to the spacing between adjacent CuO 2 layers s at sufficiently high magnetic field near H c2

High temperature superconductors applications in telecommunications

Energy Technology Data Exchange (ETDEWEB)

Kumar, A.A.; Li, J.; Zhang, M.F. [Prairie View A& M Univ., Texas (United States)

1994-12-31

The purpose of this paper is twofold: to discuss high temperature superconductors with specific reference to their employment in telecommunications applications; and to discuss a few of the limitations of the normally employed two-fluid model. While the debate on the actual usage of high temperature superconductors in the design of electronic and telecommunications devices-obvious advantages versus practical difficulties-needs to be settled in the near future, it is of great interest to investigate the parameters and the assumptions that will be employed in such designs. This paper deals with the issue of providing the microwave design engineer with performance data for such superconducting waveguides. The values of conductivity and surface resistance, which are the primary determining factors of a waveguide performance, are computed based on the two-fluid model. A comparison between two models-a theoretical one in terms of microscopic parameters (termed Model A) and an experimental fit in terms of macroscopic parameters (termed Model B)-shows the limitations and the resulting ambiguities of the two-fluid model at high frequencies and at temperatures close to the transition temperature. The validity of the two-fluid model is then discussed. Our preliminary results show that the electrical transport description in the normal and superconducting phases as they are formulated in the two-fluid model needs to be modified to incorporate the new and special features of high temperature superconductors. Parameters describing the waveguide performance-conductivity, surface resistance and attenuation constant-will be computed. Potential applications in communications networks and large scale integrated circuits will be discussed. Some of the ongoing work will be reported. In particular, a brief proposal is made to investigate of the effects of electromagnetic interference and the concomitant notion of electromagnetic compatibility (EMI/EMC) of high T{sub c} superconductors.

Properties of amorphous and microcrystalline superconductors

International Nuclear Information System (INIS)

Johnson, W.L.; Poon, S.J.

1975-01-01

Results of x-ray diffraction, electrical resistivity, critical field(H/sub c2/) and transport measurements are presented and discussed for bulk amorphous and microcrystalline transition metal alloys (Au--La, Nb--Rh, Nb--Ni--Rh, and Pd--Zr) obtained by liquid quenching. The transition temperature of the alloys is in the range 1.5 to 4.7 0 K. The J/sub c/--H/sub c2/--T/sub c/ relations are rather simple for this class of material and are compared with the theories of type II superconductors. The high resistance of bulk metallic glass to radiation damage might render them suitable for magnetic field applications in high radiation environments

Deformation of high-temperature superconductors

International Nuclear Information System (INIS)

Goretta, K.C.; Routbort, J.L.; Miller, D.J.; Chen, N.; Dominguez-Rodriguez, A.; Jimenez-Melendo, M.; De Arellano-Lopez, A.R.

1994-08-01

Of the many families of high-temperature superconductors, only the properties of those discovered prior to 1989 - Y-Ba-Cu-O, Tl-Ba(Sr)-Ca-Cu-O, and Bi(Pb)-Sr-Ca-Cu-O - have been studied extensively. Deformation tests have been performed on YBa 2 Cu 3 O x (Y-123), YBa 2 Cu 4 O x (Y-124), TlBa 2 Ca 2 Cu 3 O x (Bi-2223). The tests have revealed that plasticity is generally limited in these compounds and that the rate-controlling diffusional kinetics for creep are very slow. Nevertheless, hot forming has proved to be quite successful for fabrication of bulk high-temperature superconductors, so long as deformation rates are low or large hydrostatic stresses are applied. Steady-state creep data have proved to be useful in designing optimal heat treatments for superconductors and in support of more-fundamental diffusion experiments. The high-temperature superconductors are highly complex oxides, and it is a challenge to understand their deformation responses. In this paper, results of interest and operant creep mechanisms will be reviewed

Positron lifetime studies in undoped and Sr doped La2CuO4

International Nuclear Information System (INIS)

Sundar, C.S.; Bharathi, A.; Hariharan, Y.; Vasumathi, D.

1992-01-01

The results of positron lifetime measurements as a function of temperature, in undoped and Sr doped La 2 CuO 4 are presented. A second component of lifetime with a value of 225 ps is seen to develop after 100degC, whose intensity grows sharply in the range of 100degC to 250degC. The mean lifetime increases from 170 ps to 207 ps as the temperature is increased from room temperature to 300degC. Using the results of the theoretical calculations of positron lifetimes at vacancies in La 2 CuO 4 , it is argued that the increase in lifetime with temperature is due to positron trapping at the thermally generated La vacancies. From a two state trapping model analysis, the formation energy is estimated to be 0.39±0.04 eV

Photoemission study of absorption mechanisms in Bi2.0Sr1.8Ca0.8La0.3Cu2.1O8+δ, BaBiO3, and Nd1.85Ce0.15CuO4

International Nuclear Information System (INIS)

Lindberg, P.A.P.; Shen, Z.; Wells, B.O.; Dessau, D.S.; Ellis, W.P.; Borg, A.; Kang, J.; Mitzi, D.B.; Lindau, I.

1989-01-01

Photoemission measurements in the constant-final-state (absorption) mode were performed on three different classes of high-temperature superconductors Bi 2.0 Sr 1.8 Ca 0.8 La 0.3 Cu 2.1 O 8+δ , BaBiO 3 , and Nd 1.85 Ce 0.15 CuO 4 using synchrotron radiation from 20 to 200 eV. Absorption signals from all elements but Ce are identified. The results firmly show that the Bi 6s electrons are more delocalized in BaBiO 3 than in Bi 2.0 Sr 1.8 Ca 0.8 La 0.3 Cu 2.1 O 8+δ , in agreement with the results of band-structure calculations. Differences in the absorption signals due to O and Bi excitations between BaBiO 3 and Bi 2.0 Sr 1.8 Ca 0.8 La 0.3 Cu 2.1 O 8+δ are discussed. Delayed absorption onsets attributed to giant resonances (Ba 4d→4f, La 4d→4f, and Nd 4d→4f transitions) are also reported

Novel β-C3N4/CuO nanoflakes: facile synthesis and unique photocatalytic performance

Science.gov (United States)

Zou, Lan-Rong; Huang, Gui-Fang; Li, Dong-Feng; Tian, Qing-Nan; Yang, Ke; Si, Yuan; Chang, Shengli; Zhang, Xue-Ao; Huang, Wei-Qing

2017-09-01

For the first time, novel β-C3N4/CuO composites with superior photocatalytic activity are successfully fabricated via a facile reflux method followed by a thermal process. The morphologies, particle size and microstructure of the synthesized β-C3N4/CuO composites largely depended upon copper chloride and the volume ratio of V water:V ethanol in the mixed precursors. The fabricated β-C3N4/CuO nanoflakes exhibited obviously enhanced visible light photocatalytic activity for the degradation of methylene blue (MB) with an  ˜3.4 and 1.9 fold increase in efficiency over that of pure g-C3N4 and commercial P25, respectively. The β-C3N4/CuO composite photocatalyst also showed photocatalytic activity for the degradation of methyl orange (MO). Moreover, the β-C3N4/CuO nanoflakes showed almost no loss of photocatalytic activity after three recycles of the degradation of the MB. A multiple synergetic mechanism in β-C3N4/CuO nanoflakes, which is featured by the highly reactive {0 0 2} facets, exposed many active sites of nanoflakes and the efficient charge separation are proposed to account for the distinguished photocatalytic activity. This work provides a facile and cost-effective strategy for designing novel β-C3N4/CuO photocatalysts for application in environmental purification.

Superconductivity in hydrogen-rich materials at high pressures

Energy Technology Data Exchange (ETDEWEB)

Drozdov, Alexander

2016-07-01

A room temperature superconductor is probably one of the most desired systems in solid state physics. The highest critical temperature (T{sub c}) that has been achieved so far is in the copper oxide system: 133 kelvin (K) at ambient pressure ([82]Schilling et al. 1993) and 160 K under pressure ([42]Gao et al. 1994). The nature of superconductivity in the cuprates and in the recently discovered iron-based superconductor family (T{sub c}=57 K) is still not fully understood. In contrast, there is a class of superconductors which is well-described by the Bardeen, Cooper, Schrieffer (BCS) theory - conventional superconductors. Great efforts were spent in searching for high-temperature (T{sub c} > 77 K) conventional superconductor but only T{sub c} = 39 K has been reached in MgB2 ([68]Nagamatsu et al. 2001). BCS theory puts no bounds for T{sub c} as follows from Eliashberg's formulation of BCS theory. T{sub c} can be high, if there is a favorable combination of high-frequency phonons, strong electron-phonon coupling, and a high density of states. It does not predict however in which materials all three parameters are large. At least it gives a clear indication that materials with light elements are favorable as light elements provide high frequencies in the phonon spectrum. The lightest element is hydrogen, and Ashcroft made a first prediction that metallic hydrogen will be a high-temperature superconductor ([6]Ashcroft 1968). As pressure of hydrogen metallization was too high (about 400-500 GPa) for experimental techniques then he proposed that compounds dominated by hydrogen (hydrides) also might be good high temperature superconductors ([6]Ashcroft 1968; [7]Ashcroft 2004). A lot of the followed calculations supported this idea. T{sub c} in the range of 50-235 kelvin was predicted for many hydrides. Unfortunately, only a moderate T{sub c} of 17 kelvin has been observed experimentally ([27]Eremets et al. 2008) so far. A goal of the present work is to find a

Formation pathways in the synthesis and properties of (Tl0.5Pb0.5)(Sr0.9Ba0.1)2Ca2Cu3Oz and (Tl0.5Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3Oz-1223 superconductors

International Nuclear Information System (INIS)

Auinger, M; Gritzner, G; Bertrand, Ch; Galez, Ph; Soubeyroux, J-L

2007-01-01

The formation pathway of (Tl 0.5 Pb 0.5 )(Sr 0.9 Ba 0.1 ) 2 Ca 2 Cu 3 O z and (Tl 0.5 Pb 0.5 )(Sr 0.8 Ba 0.2 ) 2 Ca 2 Cu 3 O z was studied by neutron and x-ray diffraction. The following reaction pathway was proposed: thallium oxide and lead oxide react with Sr-rich (Sr 1-x Ca x )CuO 2 and Ca-rich (Ca x Sr 1-x )O to form Sr 4 Tl 2 O 7 and (Ca x Sr 1-x )PbO 3 , respectively. The thallate and the plumbate compounds then form the (Tl 0.5 Pb 0.5 )-1212 phase starting at a temperature of 600 deg. C. Finally, between 850 and 900 deg. C, the 1223 phase is formed from (Tl 0.5 Pb 0.5 )-1212 (Ca x Sr 1-x ) 2 CuO 3 and CuO. Parallel experiments to fabricate the (Tl, Pb)-1223 superconductor resulted in specimens with critical temperatures of 117.5 K and 116 K, respectively, and transition widths of 2 K. Differences between the pathways for the formation of Pb-doped, Sr-rich and Pb-free, Ba-rich Tl-1223 superconductors are discussed

Thermal history dependence of superconducting properties in La2CuO4+δ

International Nuclear Information System (INIS)

Hirayama, T.; Nakagawa, M.; Sumiyama, A.; Oda, Y.

1998-01-01

We studied the thermal history dependence of the superconducting properties below/above room temperature (RT) in the ceramic La 2 CuO 4-δ with excess oxygen. The phase separation (O-rich phase: superconducting and O-poor phase: antiferromagnetic) was concluded to occur above 373 K, in contrast with the usual report of the phase separation around 320 K. As for the superconducting phases, the well-known T c onset of 32 or 36 K, dependent on thermal history around 200 K, in the samples annealed in high-pressure oxygen gas, was not changed by thermal history between RT and 373 K. The samples electrochemically oxidized at RT included the phase with the high T c of 45 K, which was not changed by thermal history below RT, and the phase with the low T c of 32 or 36 K. The 45 K phase was changed into the low-T c phase by annealing at 373 K. The samples electrochemically oxidized at 333 K, which was accompanied with the diffusion of excess oxygen, showed gradual change of superconducting behavior: the single low-T c (32 or 36 K) phase (oxidation time = 24 h), coexistence of the low-T c phase and the high-T c (45 K) phase (36 h), and the single high T c phase (48 and 72 h). Thus, the single superconducting phase with the high T c of 45 K has been obtained, which showed a metallic behavior in normal resistivity and apparent changes of lattice constant in comparison with that of stoichiometric La 2 CuO 4 . (orig.)

Cu charge fluctuations and anomalous behaviour in the phonon spectrum of La2CuO4

International Nuclear Information System (INIS)

Dobry, A.; Greco, A.; Migoni, R.; Stachiotti, M.

1991-09-01

The additional excitation observed in the phonon spectrum of La 2 CuO 4 is shown to arise from Cu charge fluctuations. A nonlinear breathing shell model is formulated for the coupling of these fluctuations with the lattice. The harmonic dynamics and exact nonlinear solutions are studied in a 2-D model of the CuO 2 planes. A molecular dynamics simulation shows an additional peak of nonphononic character originated by the nonlinear lattice dynamics. (author). 20 refs, 3 figs

Study of magnetic excitations in the high critical temperature La{sub 2-x}Sr{sub x}CuO{sub 4} superconductor with neutrons inelastic scattering; Etude des excitations magnetiques dans le supraconducteur a haute temperature critique La{sub 2-x}Sr{sub x}CuO{sub 4} par diffusion inelastique des neutrons

Energy Technology Data Exchange (ETDEWEB)

Petit, S

1997-11-25

In this work, we question the relevance of spin correlations in the problem of high-T{sub c} superconductivity. To characterize these correlations, we present a detailed inelastic neutron scattering study of the magnetic excitations spectrum, in the high T{sub c} La{sub 2-x}Sr{sub x}CuO{sub 4} copper oxide superconductor, as a function of temperature and strontium content x. Our study demonstrates the existence of two distinct types of fluctuations. The first type corresponds to two-dimensional isotropic fluctuations peaked at incommensurate points around the antiferromagnetic wavevector. These fluctuations show a gap below T{sub c}. The second type of fluctuations corresponds to two-dimensional very low energy, typically 1 MeV, antiferromagnetic correlations. They arise at low temperatures, for T {<=}T{sub f} {approx} 10 K {<=}T{sub c}. Different scenarios are discussed, namely particle-hole excitation arising because of nesting properties of the Fermi surface, stripes, and localized carriers in the CuO{sub 2} plane because of the La/Sr substitution disorder. Next, aiming to study the interrelation between magnetism and superconductivity, we present a theoretical perturbative treatment of the t-t`-J model. This model is believed to describe the physics of the CuO{sub 2} plane. The considered quasiparticles describe the motion of a doped hole, followed by localized spins on the copper sites. For a given doping x, two phases can exist, containing either x or 1 + x of these quasiparticles. We show at in the second phase, the exchange interaction between localized spins, combined to the intrinsic anharmonicity of these quasiparticles leads to an attractive interaction between them. We study the stability and the symmetry of a superconducting phase based on this mechanism. (author) 215 refs.

Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples; Medidas de transporte em supercondutores: corrente critica de supercondutores granulares de alta temperatura critica

Energy Technology Data Exchange (ETDEWEB)

Passos, W.A.C., E-mail: wagner.passos@univasf.edu.br [Universidade Federal do Vale do Sao Francisco (IPCM/UNIVASF), Juazeiro do Norte, BA (Brazil). Instituto de Pesquisas em Ciencia dos Materiais; Silva, E.B. [Companhia Energetica do Sao Francisco (CHESF), Recife, PE (Brazil)

2016-07-01

This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa{sub 2}Cu{sub 3}O{sub 7-δ} sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T{sub c} of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

Positron Annihilation Studies of the Electronic Structure of Selected High-Temperature Cuprate and Organic Superconductors.

Science.gov (United States)

Chan, Lie Ping

The understanding of the electronic structure of the high-T_{c} superconductors could be important for a full theoretical description of the mechanism behind superconductivity in these materials. In this thesis, we present our measurements of the positron -electron momentum distributions of the cuprate superconductors Bi_2Sr_2CaCu _2O_8, Tl _2Ba_2Ca _2Cu_3O_ {10}, and the organic superconductor kappa-(BEDT)_2Cu(NCS) _2. We use the positron Two-dimensional Angular Correlation of Annihilation Radiation technique to make the measurements on single crystals and compare our high-statistics data with band structure calculations to determine the existence and nature of the respective Fermi surfaces. The spectra from unannealed Bi _2Sr_2CaCu _2O_8 exhibit effects of the superlattice modulation in the BiO_2 layers, and a theoretical understanding of the modulation effects on the electronic band structure is required to interpret these spectra. Since the present theory does not consider the modulation, we have developed a technique to remove the modulation effects from our spectra, and the resultant data when compared with the positron -electron momentum distribution calculation, yield features consistent with the predicted CuO_2 and BiO_2 Fermi surfaces. In the data from unannealed Tl_2Ba _2Ca_2Cu_3 O_{10}, we only observe indications of the TlO Fermi surfaces, and attribute the absence of the predicted CuO_2 Fermi surfaces to the poor sample quality. In the absence of positron-electron momentum calculations for kappa-(BEDT)_2Cu(NCS) _2, we compare our data to electronic band structure calculations, and observed features suggestive of the predicted Fermi surface contributions from the BEDT cation layers. A complete positron-electron calculation for kappa-(BEDT)_2 Cu(NCS)_2 is required to understand the positron wavefunction effects in this material.

Homogeneous samples of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

Energy Technology Data Exchange (ETDEWEB)

Hoogenboom, B.W.; Kadowaki, K.; Revaz, B.; Fischer, O

2003-09-15

Recently, much attention has been paid to inhomogeneity in samples of the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. In this work it is shown that homogeneous samples can indeed be obtained in the slightly overdoped range. However, the homogeneity critically depends on sample preparation.

Effect of magnetic ion Ni doping for Cu in the CuO{sub 2} plane on electronic structure and superconductivity on Y123 cuprate

Energy Technology Data Exchange (ETDEWEB)

Cao Shixun; Li Pinglin; Cao Guixin; Zhang Jincang

2003-05-15

The YBa{sub 2}Cu{sub 3-x}Ni{sub x}O{sub 7-{delta}} with x=0-0.4 have been studied using positron annihilation technique. The changes of positron annihilation parameters with the Ni substitution concentration x are given. From the change of electronic density n{sub e} and T{sub c}, it would prove that the localized carriers (electron and hole) in Cu-O chain and CuO{sub 2} planes have enormous influence on superconductivity by affecting charge transfer between the reservoir layer and CuO{sub 2} planes.

Temperature dependence of the electronic structure of La2CuO4 in the multielectron LDA+GTB approach

International Nuclear Information System (INIS)

Makarov, I. A.; Ovchinnikov, S. G.

2015-01-01

The band structure of La 2 CuO 4 in antiferromagnetic and paramagnetic phases is calculated at finite temperatures by the multielectron LDA+GTB method. The temperature dependence of the band spectrum and the spectral weight of Hubbard fermions is caused by a change in the occupation numbers of local multielectron spin-split terms in the antiferromagnetic phase. A decrease in the magnetization of the sublattice with temperature gives rise to new bands near the bottom of the conduction band and the top of the valence band. It is shown that the band gap decreases with increasing temperature, but La 2 CuO 4 remains an insulator in the paramagnetic phase as well. These results are consistent with measurements of the red shift of the absorption edge in La 2 CuO 4 with increasing temperature

High pressure study of high-temperature superconductors

Energy Technology Data Exchange (ETDEWEB)

Souliou, Sofia-Michaela

2014-09-29

The current thesis studies experimentally the effect of high external pressure on high-T{sub c} superconductors. The structure and lattice dynamics of several members of the high-T{sub c} cuprate and Fe-based superconductors families were investigated by means of Raman spectroscopy and X-ray diffraction under well-controlled, hydrostatic high pressure and low temperature conditions. The lattice dynamics of the high-T{sub c} superconductor YBa{sub 2}Cu{sub 3}O{sub 6+x} have been investigated systematically by Raman spectroscopy as a function of doping (x = 0.95, 0.75, 0.60, 0.55, and 0.45) and external pressure. Under ambient pressure conditions, in addition to the Raman modes expected from group theory, we observe new Raman active phonons upon cooling the underdoped samples, at temperatures well above the superconducting transition temperature. The doping dependence and the onset temperatures of the new Raman features suggest that they are associated with the incommensurate charge density wave (CDW) state recently discovered in underdoped cuprates using synchrotron X-ray scattering techniques. Under high pressure conditions (from 2 to 12 GPa), our Raman measurements on highly ordered underdoped YBa{sub 2}Cu{sub 3}O{sub 6.55} samples do not show any of the new Raman phonons seen at ambient pressure. High pressure and low temperature Raman measurements have been performed on the underdoped superconductor YBa{sub 2}Cu{sub 4}O{sub 8}. A clear renormalization of some of the Raman phonons is seen below T{sub c} as a result of the changes in the phonon self-energy upon the opening of the superconducting gap, with the most prominent one being that of the B{sub 1g}-like buckling phonon mode. The amplitude of this renormalization strongly increases with pressure, resembling the effect of hole doping in YBa{sub 2}Cu{sub 3}O{sub 6+x}. At ∝ 10 GPa, the system undergoes a reversible pressure-induced structural phase transition to a non-centrosymmmetric structure (space group

Peroxymonosulfate activation and pollutants degradation over highly dispersed CuO in manganese oxide octahedral molecular sieve

Science.gov (United States)

Li, Jun; Ye, Peng; Fang, Jia; Wang, Manye; Wu, Deming; Xu, Aihua; Li, Xiaoxia

2017-11-01

Manganese oxide octahedral molecular sieves (OMS-2) supported CuO catalysts were synthesized, characterized and used in the removal of Acid Orange 7 (AO7) in aqueous solution by an oxidation process involving peroxymonosulfate (PMS). It was found that the CuO species were highly dispersed in OMS-2 with a high ratio of easily reduced surface oxygen species. The synergetic effect between CuO and OMS-2 significantly improved the dye degradation rate and catalytic stability, compared with CuO, OMS-2 and supported CuO on other materials. About 97% of the dye was removed within 15 min at neutral solution pH by using 0.2 g/L of CuO/OMS-2 and PMS. The effect of initial solution pH, PMS concentration, reaction temperature and CuO content in the composites on AO7 degradation was also investigated. Mechanism study indicated that SO4-rad radicals generated from the interaction between PMS and Mn and Cu species with different oxidation states, mainly accounted for the degradation.

Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose

Science.gov (United States)

Meher, Sumanta Kumar; Rao, G. Ranga

2013-02-01

In the quest to enhance the selectivity and sensitivity of novel structured metal oxides for electrochemical non-enzymatic sensing of glucose, we report here a green synthesis of unique sandwich-structured CuO on a large scale under microwave mediated homogeneous precipitation conditions. The physicochemical studies carried out by XRD and BET methods show that the monoclinic CuO formed via thermal decomposition of Cu2(OH)2CO3 possesses monomodal channel-type pores with largely improved surface area (~43 m2 g-1) and pore volume (0.163 cm3 g-1). The fascinating surface morphology and pore structure of CuO is formulated due to homogeneous crystallization and microwave induced self assembly during synthesis. The cyclic voltammetry and chronoamperometry studies show diffusion controlled glucose oxidation at ~0.6 V (vs. Ag/AgCl) with extremely high sensitivity of 5342.8 μA mM-1 cm-2 and respective detection limit and response time of ~1 μM and ~0.7 s, under a wide dynamic concentration range of glucose. The chronoamperometry measurements demonstrate that the sensitivity of CuO to glucose is unaffected by the absence of dissolved oxygen and presence of poisoning chloride ions in the reaction medium, which essentially implies high poison resistance activity of the sandwich-structured CuO. The sandwich-structured CuO also shows insignificant interference/significant selectivity to glucose, even in the presence of high concentrations of other sugars as well as reducing species. In addition, the sandwich-structured CuO shows excellent reproducibility (relative standard deviation of ~2.4% over ten identically fabricated electrodes) and outstanding long term stability (only ~1.3% loss in sensitivity over a period of one month) during non-enzymatic electrochemical sensing of glucose. The unique microstructure and suitable channel-type pore architecture provide structural stability and maximum accessible electroactive surface for unimpeded mobility of glucose as well as the

Growth of high-temperature superconductor crystals from flux

International Nuclear Information System (INIS)

Demianets, L.N.; Bykov, A.B.; Melnikov, O.K.; Stishov, S.M.

1991-01-01

Crystallization of high-temperature superconductors was studied in La-Sr-Cu-O, Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems. Platelet crystals YBa 2 Cu 3 Osub(6.5+x) were obtained by spontaneous crystallization from homogeneous nonstoichiometric melts enriched in barium and copper oxides. Lasub(2-x)Sr x CuO 4 was prepared by slow cooling of melts enriched in copper oxide. Bi 2 (Sr, Ca)sub(n+1)Cu n O y , (n=1;2) was obtained by melting zone travelling. The crystals show transition to superconducting state at T=93K, ΔT 0.2-0.5 K (Y, Ba cuprate), T=87K, ΔT 2K (Bi, Sr, Ca-cuprate). La, Sr-cuprate single crystals obtained by Czochralski method did not show transition to superconducting state. For flux-grown crystals T c was 5-26 K depending on the composition, growth and heat treatment. The short characterization of some accessory phases (Ba 3 Y 2 Cu 3 PtO 10 , Casub(1.75)Srsub(1.5)Cusub(0.75)PtO 6 , BaCuO 2 , Ba 41 Cu 44 O 84 Cl 2 ) is reported. (author). 15 ref s., 8 figs

Novel-structured electrospun TiO2/CuO composite nanofibers for high efficient photocatalytic cogeneration of clean water and energy from dye wastewater.

Science.gov (United States)

Lee, Siew Siang; Bai, Hongwei; Liu, Zhaoyang; Sun, Darren Delai

2013-08-01

It is still a challenge to photocatalytically cogenerate clean water and energy from dye wastewater owing to the relatively low photocatalytic efficiency of photocatalysts. In this study, novel-structured TiO2/CuO composite nanofibers were successfully fabricated via facile electrospinning. For the first time, the TiO2/CuO composite nanofibers demonstrated multifunctional ability for concurrent photocatalytic organic degradation and H2 generation from dye wastewater. The enhanced photocatalytic activity of TiO2/CuO composite nanofibers was ascribed to its excellent synergy of physicochemical properties: 1) mesoporosity and large specific surface area for efficient substrate adsorption, mass transfer and light harvesting; 2) red-shift of the absorbance spectra for enhanced light utilization; 3) long nanofibrous structure for efficient charge transfer and ease of recovery, 4) TiO2/CuO heterojunctions which enhance the separation of electrons and holes and 5) presence of CuO which serve as co-catalyst for the H2 production. The TiO2/CuO composite nanofibers also exhibited rapid settleability by gravity and uncompromised reusability. Thus, the as-synthesized TiO2/CuO composite nanofibers represent a promising candidate for highly efficient concurrent photocatalytic organic degradation and clean energy production from dye wastewater. Copyright © 2013 Elsevier Ltd. All rights reserved.

Positron annihilation study of the high-T{sub c} (Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconductor

Energy Technology Data Exchange (ETDEWEB)

Lim, H.J. [Utah Univ., Salt Lake City, UT (United States). Dept. of Metallurgical Engineering; Byrne, J.G. [Utah Univ., Salt Lake City, UT (United States). Dept. of Metallurgical Engineering

1997-03-01

Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high-T{sub c} lead-doped Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters (S, W, and S/W) showed significant change through T{sub c}. This may result from having the highest positron density in the open BiO{sub 2} double layers and no significant positron density in the superconducting CuO{sub 2} layers where positrons, if mainly present, are known to be sensitive to the transition in other high-T{sub c} superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample ({tau}{sub 1}) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample ({tau}{sub 2}) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps. (orig.).

Possibility of the vortex-antivortex transition temperature of a thin-film superconductor being renormalized by disorder

International Nuclear Information System (INIS)

Hebard, A.F.; Kotliar, G.

1989-01-01

The universal relation between the Kosterlitz-Thouless transition temperature T/sub c/ and the superfluid sheet density of thin-film superconductors with mean-field transition temperature T/sub c/ 0 results in a monotonically decreasing dependence of the ratio T/sub c//T/sub c0/ on the normal-state sheet resistance R/sub n/. Ambiguity in the experimental definition of R/sub n/ in highly disordered thin-film superconductors is addressed by reexamining previously published data on amorphous composite In/InO/sub x/ films. Arguments are presented in favor of using the zero-temperature value of R/sub n/, a quantity obtained by extrapolation. The dependence of T/sub c//T/sub c0/ on R/sub n/ that results from such a choice is in agreement with theory for dirty superconductors and thus suggests that additional corrections to T/sub c/ in the presence of extreme disorder are not required

Phase compatibilities of YBa2Cu3O(9-delta) type structure in quintenary systems Y-Ba-Cu-O-X (impurity)

Science.gov (United States)

Karen, P.; Fjellvag, H.; Kjekshus, A.

1990-01-01

Electrical transport properties of the oxidic high T(sub c) superconductors are significantly affected by the presence of minor amounts of various elements adventing as impurities, e.g., from the chemical environment during manufacturing. YBa2Cu3O(9-delta) is prone to an extinction of the superconductivity on (partial) substitution of all four elemental components. E.g., Pr (for Y), La (for Ba), Zn (for Cu) or peroxygroup (for O) substituents will alter some of the superconductivity preconditions, like mixed valence state in Cu3O7/O(9-delta) network or structural distortion of the network. Although various pseudoternary chemical equilibrium phase diagrams of the Y(O)-Ba(O)-Cu(O) system now are available, no consensus is generally shown, however, this is partly due to lack of compatible definitions of the equilibrium conditions. Less information is available about the phase compatibilities in the appropriate quaternary phase diagram (including oxygen) and virtually no information exists about any pentenary phase diagrams (including one impurity). Unfortunately, complexity of such systems, stemming both from number of quaternary or pentenary compounds and from visualizing the five-component phase system, limits this presentation to more or less close surroundings of the YBa2Cu3O(9-delta) type phase in appropriate pseudoquaternary or pseudopseudoternary diagrams, involving Y-Ba-Cu and O, O-CO2, alkaline metals, Mg and alkaline earths, and Sc and most of the 3-d and 4-f elements. The systems were investigated by means of x ray diffraction, neutron diffraction and chemical analytical methods on samples prepared by sol-gel technique from citrates. The superconductivity was characterized by measuring the diamagnetic susceptibility by SQUID.

Reply to Comment on ‘Oxygen vacancy-induced magnetic moment in edge-sharing CuO2 chains of Li2CuO2-δ ’

Science.gov (United States)

Shu, G. J.; Tian, J. C.; Lin, C. K.; Hayashi, M.; Liou, S. C.; Chen, W. T.; Wong, Deniz P.; Liou, H. L.; Chou, F. C.

2018-05-01

In this reply to the comment on ‘Oxygen vacancy-induced magnetic moment in edge-sharing CuO2 chains of {{{Li}}}2{{{CuO}}}2-δ ’ (2017 New Journal of Physics 19 023206), we have clarified several key questions and conflicting results regarding the size of the intra-chain nearest neighbor coupling J 1 and the sign of the Weiss temperature Θ defined in the Curie–Weiss law of χ(T) = χ ◦ + C/(T ‑ Θ). Additional data analysis is conducted to verify the validity of the Curie–Weiss law fitting protocol, including the negative sign and size of Θ based on the high-temperature linear temperature dependence of 1/χ(T) for T > J 1 and \\tfrac{g{μ }B{SH}}{{k}BT}\\ll 1. The consistency between the magnetic antiferromagnetic (AF) ground state below T N and the negative sign of Θ in the high-temperature paramagnetic (PM) state is explained via the reduction of thermal fluctuation for a temperature-independent local field due to magnetic interaction of quantum nature. A magnetic dipole–dipole (MDD)-type interaction among FM chains is identified and proposed to be necessary for the 3D AF magnetic ground state formation, i.e., the Heisenberg model of an exchange-type interaction alone is not sufficient to fully describe the quasi-1D spin chain system of {{{Li}}}2{{{CuO}}}2. Several typical quasi-1D spin chain compounds, including {{{Li}}}2{{{CuO}}}2,{{{CuAs}}}2{{{O}}}4,{{{Sr}}}3{{{Fe}}}2{{{O}}}5, and CuGeO3, are compared to show why different magnetic ground states are achieved from the chemical bond perspective.

Electronic Structure of the Bismuth Family of High Temperature Superconductors

Energy Technology Data Exchange (ETDEWEB)

Dunn, Lisa

2002-03-07

large superconducting phase transition temperature in a high temperature superconductor is associated with parameters that cause both large pairing strength and strong phase coherence in the system. The number of CuO2 layers in each unit cell is just one of the factors that affect these parameters.

Single crystal NMR studies of high temperature superconductors

International Nuclear Information System (INIS)

Pennington, C.H.; Durand, D.J.; Zax, D.B.; Slichter, C.P.; Rice, J.P.; Bukowski, E.D.; Ginsberg, D.M.

1989-01-01

The authors report Cu NMR studies in the normal state of a single crystal of the T/sub c/ = 90 K superconductor YBa 2 Cu 3 O/sub 7/minus/δ/. The authors have measured the magnetic shift tensor, the electric field gradient tensor, the nuclear spin-lattice relaxation rate tensor, and the time dependence and functional form of the transverse decay. From these data they obtain information about the charge state and magnetic state of the Cu atoms, and the existence and size of the electronic exchange coupling between spins of adjacent Cu atoms. 18 refs., 3 figs., 2 tabs

Unusually high critical current of P-doped BaFe{sub 2}As{sub 2} single crystalline thin film

Energy Technology Data Exchange (ETDEWEB)

Kurth, Fritz; Engelmann, Jan; Schultz, Ludwig [IMW, IFW Dresden, Dresden (Germany); TU Dresden, Dresden (Germany); Tarantini, Chiara; Jaroszynski, Jan [ASC, NHMFL, Florida (United States); Grinenko, Vadim; Reich, Elke; Huehne, Ruben [IMW, IFW Dresden, Dresden (Germany); Haenisch, Jens [IMW, IFW Dresden, Dresden (Germany); ITEP, KIT, Karlsruhe (Germany); Mori, Yasohiro; Sakagami, Akihiro; Kawaguchi, Takahiko; Ikuta, Hiroshi [Department of Crystalline Materials Science, Nagoya University, Nagoya (Japan); Holzapfel, Bernhard [ITEP, KIT, Karlsruhe (Germany); Iida, Kazumasa [IMW, IFW Dresden, Dresden (Germany); Department of Crystalline Materials Science, Nagoya University, Nagoya (Japan)

2015-07-01

Microstructurally clean, isovalently P-doped BaFe{sub 2}As{sub 2} single crystalline thin films have been prepared by molecular beam epitaxy. These films show a superconducting transition temperature (T{sub c}) of over 30 K and high transport self-field critical current densities (J{sub c}) of over 6 MA/cm{sup 2} at 4.2 K, which are among the highest for Fe based superconductors. In-field J{sub c} exceeds 0.1 MA/cm{sup 2} at μ{sub 0}H = 35 T for H parallel ab and μ{sub 0}H = 18 T for H parallel c, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar T{sub c}. This unusually high J{sub c} makes P-doped Ba-122 very favorable for high-field magnet applications.

Role of Coulomb repulsion in multilayer cuprate superconductor

International Nuclear Information System (INIS)

Singh Chauhan, Ekta; Singh, Vipul; Masih, Piyush

2012-01-01

Although BCS theory completely neglects coulomb repulsion; Anderson and Morel showed very early that it plays a central role in superconductivity. Since all high T c superconductors are based on the structure of closely spaced square planner CuO 2 layers and role of interlayer interaction plays important role in enhancement of T c . Therefore the work has been dealt with 'Role of Coulomb repulsion in Multilayer Cuprate Superconductors'. An expression for transition temperature T c is obtained by using simple integration technique and is numerically solved. It has found that T c decreases with electronic repulsion. (author)

Application of superconductors - High T/sub c/ and otherwise-to electric power generators

International Nuclear Information System (INIS)

Kirtley, J.L. Jr.

1988-01-01

Because superconducting magnets are capable of making large magnetic fluxes over large volumes of space with no dissipation and without the need for iron magnetic circuits, they appear to offer distinct advantages for use in electric machinery. In addition to eliminating the field winding losses, superconductors help improve efficiency by increasing flux density, thus shortening the armature conductor length per unit of flux linked. The elimination of iron allows for innovations in generator design and reduces reactance, thus improving dynamic performance. The basic feasibility of using metallic superconductors, operating at liquid helium temperature, has been demonstrated by investigators at several different organizations. While there is not yet agreement on exactly how a superconducting generator would be built, it is generally agreed that machines using liquid helium temperature conductors will be economically viable in at least some range of ratings. The use of higher transition temperature superconductors will make superconducting generators even more attractive if such conductors can provide satisfactory performance, measured by current density and magnetic field. Recent studies point out that even substantial improvements in operating temperature will not justify large reductions in current density

Topotactic reduction and phase transitions in (T,T′ La1.8Pr0.2CuO4

Directory of Open Access Journals (Sweden)

M.I. Houchati

2017-05-01

The X-ray powder diffraction data have revealed that this cuprate is crystallized with the so-called “pseudo-S” type structure, showing a monoclinic symmetry and space group A2/m. Concerning the EPR measurements, they have shown the presence of Cu2+ cation and a hyperfine structure suggesting a pronounced hybridization of the copper–oxygen bond. Finally, X-ray diffraction has demonstrated that the obtained La1.8Pr0.2CuO3.5, heated in oxygen at 420 °C, turns topotactically into La1.8Pr0.2CuO4 with a T′-type structure (I4/mmm.

Hormonal evaluation of T{sub 4} and T{sub 3} through radioimmunoassay in younglings of rats with hypothyroidism; Avaliacao hormonal de T{sub 4} e T{sub 3} atraves de radioimunoensaio em filhotes de ratas hipotireoideas

Energy Technology Data Exchange (ETDEWEB)

Silveira, M.F.G. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Biofisica e Radiobiologia; Silva, I.M.S.; Pereira, S.S.L.; Souza, G.M.L.; Carvalho, E.F.M.B.; Cavalcante, C.V.G. [Pernambuco Univ., Recife, PE (Brazil). Dept. de Anatomia; Lima Filho, G.L.; Catanho, M.T.J.A. [Faculdade de Formacao de Professores de Nazare da Mata, PE (Brazil). Dept. de Ciencias Naturais

2000-07-01

The onset of fetal thyroid function occurs about 17-18 days after conception in the rat. The maternal hypothyroidism which occurs during gestation provokes alteration in the rat after birth. Due to this alteration, we decided to analyze the hormonal modification in the newborn rats. The hypothyroidism was induced in normal dams, which were being treated for 7 days with MMI (in the concentration of 0,03% in drinking water) before mating. Another dam group which was submitted to an induction of hypothyroidism maintained the treatment with MMI for 13 days during gestation. The hormones were assessed by radioimmunoassay technique. It was seen that the rats which were born from hypothyroid dams suffered alterations on its T{sub 4} and T{sub 3} hormone levels concerning to 10, 30 and 60 days after birth. There was also modifications on their weight and size. The growth is affected throughout post-natal life by thyroid hormones, which has a facilitator influence on growth hormone economy, as opposed to the inhibitory effects on TSH economy. The administration of MMI bars the fetal thyroid gland function, causing a decrease of both T{sub 4} and T{sub 3} levels, even after the birth, indicating that the maternal hypothyroidism influences on the post-natal life of the rat. (author)

Enhancement of mechanical properties of 123 superconductors

Science.gov (United States)

Balachandran, U.

1995-04-25

A composition and method are disclosed of preparing YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductor. Addition of tin oxide containing compounds to YBCO superconductors results in substantial improvement of fracture toughness and other mechanical properties without affect on T{sub c}. About 5-20% additions give rise to substantially improved mechanical properties.

Morphological Control of Mesoporosity and Nanoparticles within Co3O4-CuO Electrospun Nanofibers: Quantum Confinement and Visible Light Photocatalysis Performance.

Science.gov (United States)

Pradhan, Amaresh C; Uyar, Tamer

2017-10-18

The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite Co 3 O 4 -CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (Co 3 O 4 -CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite Co 3 O 4 -CuO NFs but also single mesoporous Co 3 O 4 NFs and CuO NFs have been produced for comparison. The choice of mixed polymer templates such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for electrospinning is responsible for the formation of 1D mesoporous NFs. The HR-TEM result showed evolution of interconnected nanoparticles (NPs) and creation of mesoporosity in all electrospun NFs. The quantum confinement is due to NPs within NFs and has been proved by the surface-enhanced Raman scattering (SERS) study and the UV-vis-NRI diffuse reflectance spectra (DRS). The high intense photoluminescence (PL) spectra showing blue shift of all NFs also confirmed the quantum confinement phenomena. The lowering of PL spectrum after mixing of CuO in Co 3 O 4 nanofibers framework (Co 3 O 4 -CuO NFs) proved CuO as an efficient visible light response low cost cocatalyst/charge separator. The red shifting of the band gap in composite Co 3 O 4 -CuO NFs is due to the internal charge transfer between Co 2+ to Co 3+ and Cu 2+ , proved by UV-vis absorption spectroscopy. Creation of oxygen vacancies by mixing of CuO and Co 3 O 4 also prevents the electron-hole recombination and enhances the photocatalytic activity in composite Co 3 O 4 -CuO NFs. The photocurrent density, Mott-Schottky (MS), and electrochemical impedance spectroscopy (EIS) studies of all NFs favor the high photocatalytic performance. The mesoporous composite Co 3 O 4 -CuO NFs exhibits high photocatalytic activity toward phenolic compounds degradation as compared to the other two NFs (Co 3 O 4 NFs and CuO NFs). The kinetic study of phenolic compounds followed first order rate equation. The high photocatalytic

Electrochemical fluorination of La(2)CuO(4): a mild "chimie douce" route to superconducting oxyfluoride materials.

Science.gov (United States)

Delville, M H; Barbut, D; Wattiaux, A; Bassat, J M; Ménétrier, M; Labrugère, C; Grenier, J C; Etourneau, J

2009-08-17

The fluorination of La(2)CuO(4) was achieved for the first time under normal conditions of pressure and temperature (1 MPa and 298 K) via electrochemical insertion in organic fluorinated electrolytes and led to lanthanum oxyfluorides of general formula La(2)CuO(4)F(x). Analyses showed that, underneath a very thin layer of LaF(3) (a few atomic layers), fluorine is effectively inserted in the material's structure. The fluorination strongly modifies the lanthanum environment, whereas very little modification is observed on copper, suggesting an insertion in the La(2)O(2) blocks of the structure. In all cases, fluorine insertion breaks the translation symmetry and introduces a long-distance disorder, as shown by electron spin resonance. These results highlight the efficiency of electrochemistry as a new "chimie douce" type fluorination technique for solid-state materials. Performed at room temperature, it additionally does not require any specific experimental care. The choice of the electrolytic medium is crucial with regard to the fluorine insertion rate as well as the material deterioration. Successful application of this technique to the well-known La(2)CuO(4) material provides a basis for further syntheses from other oxides.

First observation of the nuclei {sup 45}Fe and {sup 49}Ni (T{sub Z} = - 7/2) and {sup 42}Cr (T{sub Z} = - 3); Premiere observation des noyaux {sup 45}Fe et {sup 49}Ni (T{sub Z} = - 7/2) et {sup 42}Cr (T{sub Z} = - 3)

Energy Technology Data Exchange (ETDEWEB)

Blank, B.; Czajkowski, S.; Davi, F.; Del Moral, R.; Fleury, A.; Marchand, C.; Pravikoff, M.S. [Centre d`Etudes Nucleaires, Bordeaux-1 Univ., 33 Gradignan (France); Dufour, J.P. [URA 451, Gradignan (France); Benlliure, J.; Boue, F.; Collatz, R.; Heinz, A.; Hellstroem, M.; Hu, Z.; Roeckl, E.; Shibata, M.; Suemmerer, K. [Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany); Janas, Z.; Karny, M.; Pfuetzner, M. [Institute of Experimental Physics, University of Warsaw, PL-00 681 Warszawa (Poland); Lewitowicz, M. [Grand Accelerateur National d`Ions Lourds (GANIL), 14 - Caen (France)

1997-06-01

The two-proton radioactivity from the ground states was predicted by V.I. Goldanskii; it can take place either by {sup 2}He emission or by the simultaneous emission of two spatially non-correlated protons. For the nuclei liable to this type of radioactivity the single proton emission is energetically forbidden. The two-proton decay was observed for {sup 6}Be{sup 2} and {sup 12}O{sup 3} but the Q-value of the reaction is high above the Coulomb barrier and as such does not permit a decay process of a sufficient long lifetime. Theoretical calculations by B.A. Brawn predict {sup 39}Ti, {sup 45}Fe and {sup 48}Ni as the best candidates with the 2p emission lifetime within 1{mu}s to 150 ms. Only {sup 39}Ti decay has been observed so far. As candidate for 2p radioactivity nuclei we studied {sup 38}Ti, {sup 42}Cr, {sup 45}Fe and {sup 48`49}Ni. A primary beam of {sup 58}Ni at 600 MeV/nucleon from the SIS synchrotron at GSI was used to produce proton-rich isotopes in the titanium-to-nickel region by projectile fragmentation on a beryllium target. The fragment were separated by the projectile-fragment separator FRS and unambiguously identified by means of its standard detection set-up using a ToF-{Delta}E-B{rho} analysis. We report here the first observation of the T{sub Z} = - 7/2 nuclei {sup 45}Fe and {sup 49}Ni, the most proton-rich nuclei ever synthesized with an excess and seven protons. In addition, the new isotope {sup 42}Cr (T{sub Z} -3) was also identified. These isotopes are, according to commonly used mass predictions, all unbound with respect to two-proton emission from their ground states. However, we did not observe any count corresponding to {sup 38}Ti (T{sub Z} -3) although we expected about 5 counts in a setting optimized for this isotope 6 refs.

High-temperature superconductors, as seen through the eyes of neutrons

Directory of Open Access Journals (Sweden)

Z. Yamani

2006-09-01

Full Text Available   Neutron scattering is proved to be a vital probe in unveiling the magnetic properties of high temperature superconductors (HTSC. Detailed information about the energy and momentum dependence of the magnetic dynamics of HTSC have been obtained directly by this technique. Over the past decade by improving the crystal growth methods, large and high quality single crystals of HTSC, which are essential for a neutron scattering experiment, have become available. The results of neutron scattering measurements on such crystals have considerably enhanced our understanding of the magnetism in HTSC both in the superconducting (SC and normal states. In this review, the neutron scattering results on two main HTSC families, La2-xSrxCuO4 (LSCOx and YBa2CuO3O6+x (YBCO6+x, are considered with an emphasis on the most prominent properties of these materials that are now widely accepted. These include the presence of strong antiferromagnetic (AF fluctuations even in optimally doped region of the phase diagram, neutron resonance peak that scales with SC transition temperature, Tc, incommensurate magnetic fluctuations (stripes, and a pseudogap in the normal state of underdoped materials.

Consolidation of powders of the superconductor YBa/sub 2/Cu/sub 3/O/sub 7-. delta. / by high energy-high rate processing

Energy Technology Data Exchange (ETDEWEB)

Lee, J.Y.; Persad, C.; Swinnea, J.S.; Marcus, H.L.; Steinfink, H. (Texas Univ., Austin, TX (USA). Center for Materials Science and Engineering)

1988-01-01

The consolidation response of powders of the superconducting compound YBa/sub 2/Cu/sub 3/O/sub 7-{delta}/ by itself and admixed with metal powders is reported. The processing approach relies on short duration (high current density (10/sup 4/A/cm/sup 2/), pulse resistive heating of powders under applied pressures of 200 MPa to 400 MPa. Powders and fabricated disk concepts were characterized by X-ray diffraction, optical and scanning electron microscopy.

Neutron scattering studies of two-dimensional antiferromagnetic spin fluctuations in insulating and superconducting S = 1/2 systems

International Nuclear Information System (INIS)

Bech Christensen, N.

2005-01-01

Time-of-flight and polarized triple axis neutron scattering is used to probe the spin excitations of Cu(DCOO) 2 x4D 2 O and La 2-x Sr x CuO 4 . The first part of the thesis contains an investigation of the excitation spectrum of the square lattice S = 1/2 Heisenberg antiferromagnet Cu(DCOO) 2 4D 2 O. Along the antiferromagnetic zone boundary a pronounced intensity variation is found for the dominant single-magnon excitations. This variation tracks an already known zone boundary dispersion. Using polarization analysis to separate the components of the excitation spectrum, a continuum of longitudinally polarized multimagnon excitations is discovered at energies above the single-magnon branch. At low energies, the findings are well described by linear spin wave theory. At high energies, linear spin wave theory fails and instead the data are very well accounted for by state-of-the-art Quantum Monte Carlo computations. In the second part of the thesis, the spin excitation spectra of the high temperature superconductors La 1.90 Sr 0.10 CuO 4 and La 1.84 Sr 0.16 Cu characterized. The main discovery is that the excitations are dispersive at both doping levels. The dispersion strongly resembles that seen in other high-T c superconductors. The presence of dispersive excitations does not require superconductivity to exist. For La 1.84 Sr 0.16 CuO 4 , but not for La 1.90 Sr 0.10 CuO 4 , the onset superconductivity gives rise to a spectral weight shift which displays qualitative and quantitative similarities to the resonance mode observed in other high-T c superconductors. (au)

Two decades on[Research into high-temperature superconductors

Energy Technology Data Exchange (ETDEWEB)

Durrani, M. [Physics World (United Kingdom)

2006-04-15

Research into high-temperature superconductors should focus on experiment, not theory. While the world looked on in horror at the events unfolding at the Chernobyl nuclear-power plant in the Soviet Union 20 years ago this month, another significant - but far less reported - development in the world of physics had just taken place. On 17 April 1986 a short paper by Georg Bednorz and Alexander Mueller arrived at the offices of Zeitschrift fuer Physik in Heidelberg, Germany. The two physicists, based at IBM's Zurich Research Laboratory in Switzerland, announced they had made a material from barium, lanthanum, copper and oxygen that could conduct electricity without resistance when cooled below a transition temperature, T{sub c}, of about 30 K. It was the world's first 'high-temperature' superconductor. Driven by the dream of materials that can superconduct at room temperature, experimentalists scurried back to their labs. Within a year, a T{sub c} of 90 K in another material had been reported and by October 1987 Bednorz and Mueller had been crowned with a Nobel prize. While papers on high-temperature superconductivity have continued to stream out since those heady days, progress has been slower than expected. Applications like levitating trains and resistance-free power cables are only now starting to come to market. Scientists have been unable to make superconducting wires that work much above 130 K, while a reliable theory of high-temperature superconductivity remains elusive. Even if we had such a theory, it is not clear that it would predict which materials might superconduct at room temperature. After all, the Bardeen-Cooper-Schrieffer theory, which explains the behaviour of low-temperature superconductors with admirable success, said nothing about the superconducting properties of Bednorz and Mueller's copper-oxide ceramics. What successes there have been over the last 20 years - such as the recent discoveries that iron, single crystals

Rf measurements on high T/sub c/ materials

International Nuclear Information System (INIS)

Rubin, D.L.; Gruschus, J.; Kirchgessner, J.

1988-01-01

Measurements of the microwave surface resistivity of high T/sub c/ materials were made in a superconducting niobium 6Ghz TE 011 resonant cavity and a niobium 8.6 Ghz TM 010 elliptical cavity. The TE 011 apparatus permits variation of the temperature of the sample independently of that of the niobium cavity. The Q of the host cavity thus remains at a high value while the resistivity of the sample is measured from 4.2 K to above the transition (≅ 100 K). The resistivity of a 1.27 cm diameter ceramic pellet is observed to fall from 1 Omega above transition to 0.02 Omega at 4.2 K. A set of nine single crystals of total area 6.5 mm 2 is measured to have a broad transition near 75 K. The surface resistivity of a single 3 mm 2 crystal is measured in the elliptical cavity to be ≤ 9.8 x 10 -5 Omega at 1.5 K. 4 references, 9 figures

Nd4Cu2O7: A copper(I) oxide with a novel cooperatively distorted T' type structure

International Nuclear Information System (INIS)

Pederzolli, D.R.; Attfield, J.P.

1998-01-01

The crystal structure of Nd 4 Cu 2 O 7 (monoclinic, space group A2/m, a = 8.4493(2) angstrom, b = 3.7591(1) angstrom, C = 12.6006(5) angstrom, β = 109.576(4)degree, Z = 2) prepared by topotactic reduction of the high-T c superconductor parent phase Nd 2 CuO 4 , has been determined by Rietveld fitting of time-of-flight neutron powder diffraction data (R wp = 1.90%). A novel oxygen-vacancy-ordered arrangement of cooperatively distorted Cu 2 O 3 planes containing 2- and 4-coordinate Cu + sites is found

139La and 63Cu NMR investigation of charge order in La2CuO4 +y (Tc=42 K)

Science.gov (United States)

Imai, T.; Lee, Y. S.

2018-03-01

We report 139La and 63Cu NMR investigation of the successive charge order, spin order, and superconducting transitions in superoxygenated La2CuO4 +y single crystal with stage-4 excess oxygen order at Tstage≃290 K. We show that the stage-4 order induces tilting of CuO6 octahedra below Tstage, which in turn causes 139La NMR line broadening. The structural distortion continues to develop far below Tstage, and completes at Tcharge≃60 K, where charge order sets in. This sequence is reminiscent of the the charge-order transition in Nd codoped La1.88Sr0.12CuO4 that sets in once the low-temperature tetragonal phase is established. We also show that the paramagnetic 63Cu NMR signals are progressively wiped out below Tcharge due to enhanced low-frequency spin fluctuations in charge-ordered domains, but the residual 63Cu NMR signals continue to exhibit the characteristics expected for optimally doped superconducting CuO2 planes. This indicates that charge order in La2CuO4 +y does not take place uniformly in space. In addition, unlike the typical second-order magnetic phase transitions, low-frequency Cu spin fluctuations as probed by 139La nuclear spin-lattice relaxation rate do not exhibit critical divergence at Tspin(≃Tc ) =42 K. These findings, including the spatially inhomogeneous nature of the charge-ordered state, are qualitatively similar to the case of La1.885Sr0.115CuO4 [Imai et al., Phys. Rev. B 96, 224508 (2017), 10.1103/PhysRevB.96.224508 and Arsenault et al., Phys. Rev. B 97, 064511 (2018), 10.1103/PhysRevB.97.064511], but both charge and spin order take place more sharply in the present case.

Oxygen diffusion in cuprate superconductors

Energy Technology Data Exchange (ETDEWEB)

Routbort, J.L.; Rothman, S.J.

1995-01-01

Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. This article reviews studies of the diffusion of oxygen in La{sub 2}{sub {minus}}{sub {times}}Sr{sub {times}}CuO{sub 4}, YBa{sub 2}Cu{sub 3}O{sub 7}{sub {minus}}{delta}, YBa{sub 2}Cu{sub 4}O{sub 8}, and the Bi{sub 2}Sr{sub 2}Ca{sub n}{sub {minus}}{sub 1}Cu{sub n}O{sub 2}{sub +}{sub 4} (n = 1, and 2) superconductors, and attempt to elucidate the atomic mechanisms responsible.

Positron trapping at defects in copper oxide superconductors

International Nuclear Information System (INIS)

McMullen, T.; Jena, P.; Khanna, S.N.; Li, Y.; Jensen, K.O.

1991-01-01

Positron states and lifetimes at defects in the copper oxide superconductors La 2-x Sr x CuO 4 , YBa 2 Cu 3 O 7-x , and Bi 2 Sr 2 CaCu 2 O 8+x are calculated with use of the superposed-atom model. In the Bi 2 Sr 2 CaCu 2 O 8+x compound, we find that the smaller metal-ion vacancies appear to only bind positrons weakly, while missing oxygens do not trap positrons. In contrast, metal-ion vacancies in La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-x bind positrons by ∼1 eV, and oxygen-related defects appear to be the weak-binding sites in these materials. The sites that bind positrons only weakly, by energies ∼k BT , are of particular interest in view of the complex temperature dependences of the annihilation characteristics that are observed in these materials

Development of Bulk Bi2+xSr3-yCa yCu 2O8+delta Superconductors by Partial-Melting Route for Fault Current Limiters Application

Directory of Open Access Journals (Sweden)

Bojan A. Marinkovic

2002-06-01

Full Text Available The production of bulk Bi2+xSr3-yCa yCu 2O8+delta (Bi-2212 superconductors for fault current limiter application was developed via a partial-melting route. Aiming high Ic (critical current, which is the essential superconducting characteristic for application of this material in the construction of Fault Current Limiters (FCL, the produced blocks have predominance of Bi-2212 phase (83 wt%, which characterizes with high values of zero and onset transport critical temperature of 92K and 97.5K, respectively. A relatively low transition width, deltaT, from the superconducting to the normal state of 5.5K, revealed a good intergrain connectivity. Consequently, current measurements on the blocks of Bi-2212 show promising Ic values of 230A and 850A for direct and alternate current, respectively. It is expected that further increases in the Ic values will depend on the elimination of an observed amorphous phase and further reduction of amount and grain sizes of secondary phases, still present in the blocks obtained by the proposed partial-melting route. This may be achieved by a further optimization of the partial-melting processing parameters.

Contact spectroscopy of high-temperature superconductors (Review). I - Physical and methodological principles of the contact spectroscopy of high-temperature superconductors. Experimental results for La(2-x)Sr(x)CuO4 and their discussion

Science.gov (United States)

Ianson, I. K.

1991-03-01

Research in the field of high-temperature superconductors based on methods of tunneling and microcontact spectroscopy is reviewed in a systematic manner. The theoretical principles of the methods are presented, and various types of contacts are described and classified. Attention is given to deviations of the measured volt-ampere characteristics from those predicted by simple theoretical models and those observed for conventional superconductors. Results of measurements of the energy gap and fine structure of volt ampere characteristic derivatives are presented for La(2-x)Sr(x)CuO4.

Glassy spin freezing and NMR wipeout effect in the high-T{sub c} superconductor La{sub 1.90}Sr{sub 0.10}CuO{sub 4}: Critical discussion of the role of stripes

Energy Technology Data Exchange (ETDEWEB)

Julien, M.-H.; Campana, A.; Rigamonti, A.; Carretta, P.; Borsa, F.; Kuhns, P.; Reyes, A. P.; Moulton, W. G.; Horvatic, M.; Berthier, C. (and others)

2001-04-01

We report on {sup 139}La and {sup 63}Cu NMR/NQR measurements in the high-T{sub c} superconductor La{sub 1.90}Sr{sub 0.10}CuO{sub 4}, with T{sub c}=26.5 K. Spin fluctuations probed by {sup 139}La spin-lattice relaxation (T{sub 1}) continuously slow down on cooling through T{sub c}. We argue that spin freezing and superconductivity are bulk effects in this sample. Thus both phenomena have to coexist microscopically. The distribution of {sup 139}La T{sub 1} values at low temperature reveals a wide spread of spin fluctuation frequencies in CuO{sub 2} planes. A simple estimate shows that {sup 63}Cu nuclei at sites where electronic fluctuations are the slowest are not observable (wipeout effect) because relaxation times are too short. This means that the {sup 63}Cu NQR wipeout, observed in this sample, can be explained primarily by slow magnetic, rather than charge, fluctuations. The magnetic origin of the wipeout is still compatible with a connection between wipeout and charge order [as proposed by Hunt , Phys. Rev. Lett. 82, 4300 (1999)], but this connection is indirect. On the other hand, since the wipeout fraction is not an intensive quantity it cannot define a proper order parameter and cannot be used by itself as a criterion for the existence of a stripe phase.

First principles simulation on the K0.8Fe2Se2 high-temperature structural superconductor

International Nuclear Information System (INIS)

Guo, Rui; Yang, Shizhong; Khosravi, Ebrahim; Zhao, Guang-Lin; Bagayoko, Diola

2013-01-01

Highlights: • The superconductor K 0.8 Fe 2 Se 2 super cell size, shape, and atomic positions are fully optimized using first principles density functional theory method. • Each K atom donates 0.8 |e| with K vacancies in the supercell, each Fe atom donates 0.4 |e|, while each Se atom gains 0.7 |e| ∼ 0.8 |e|. • Fe atoms show magnetic moment fluctuation and possible strong spin-orbital coupling. -- Abstract: Since the synthesis of the first ones in 2008, iron-based high temperature superconductors have been the subject of many studies. This great interest is partly due to their higher, upper magnetic field, smaller Fermi surface around the Γ point, and a larger coherence length. This work is focused on A x Fe 2 Se 2 structural superconductor (FeSe, 11 hierarchy; A = K, Cs) as recently observed. ARPES data show novel, electronic structure and a hole-free Fermi surface which is different from previously observed Fermi surface images. We use ab initio density functional theory method to simulate the electronic structure of the novel superconductor A x Fe 2 Se 2 . We compare this electronic structure with those of other Fe-based superconductors

Cryogenic milling for the fabrication of high J{sub c} MgB{sub 2} bulk superconductors

Energy Technology Data Exchange (ETDEWEB)

Kim, D. N.; Kang, M. O.; Park, H. W. [Korea University of Technology and Education, Cheonan (Korea, Republic of); Jun, B. H.; Kim, C. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2017-06-15

Cryogenic milling which is a combined process of low-temperature treatment and mechanical milling was applied to fabricate high critical current density (J{sub c}) MgB{sub 2} bulk superconductors. Liquid nitrogen was used as a coolant, and no solvent or lubricant was used. Spherical Mg (6-12 μm, 99.9 % purity) and plate-like B powder (⁓ 1 μm, 97 % purity) were milled simultaneously for various time periods (0, 2, 4, 6 h) at a rotating speed of 500 rpm using ZrO{sub 2} balls. The (Mg{sup +2B}) powders milled were pressed into pellets and heat-treated at 700°C for 1 h in flowing argon. The use of cryomilled powders as raw materials promoted the formation reaction of superconducting MgB{sub 2}, reduced the grain size of MgB{sub 2}, and suppressed the formation of impurity MgO. The superconducting critical temperature (T{sub c}) of MgB{sub 2} was not influenced as the milling time (t) increased up to 6 h. Meanwhile, the critical current density (J{sub c}) of MgB{sub 2} increased significantly when t increased to 4 h. When t increased further to 6 h, however, Jc decreased. The J{sub c} enhancement of MgB{sub 2} by cryogenic milling is attributed to the formation of the fine grain MgB{sub 2} and a suppression of the MgO formation.

Application of fast spin-echo T[sub 2]-weighted imaging for examination of the neurocranium. Comparison with the conventional T[sub 2]-weighted spin-echo sequence. Die Anwendung der T[sub 2]-gewichteten Turbo-Spin-Echo-Sequenz zur Untersuchung des Neurokraniums. Vergleich mit der konventionellen T[sub 2]-gewichteten Spin-Echo-Sequenz

Energy Technology Data Exchange (ETDEWEB)

Siewert, C. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany)); Hosten, N. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany)); Felix, R. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany))

1994-07-01

T[sub 2]-weighted spin-echo imaging is the standard screening procedure in MR imaging of the neutrocranium. We evaluated fast spin-echo T[sub 2]-weighted imaging (TT[sub 2]) of the neurocranium in comparison to conventional spin-echo T[sub 2]-weighted imaging (T[sub 2]). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher than TT[sub 2] than in T[sub 2] (with the exception of grey-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT[sub 2], Parkinson patients have to be examined by conventional T[sub 2]. If these limitations are taken into account, fast spin-echo T[sub 2]-weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T[sub 2]-weighting achieved in a short acquisition time. (orig.)

Epitaxial effects in thin films of high-Tc cuprates with the K2NiF4 structure

Science.gov (United States)

Naito, Michio; Sato, Hisashi; Tsukada, Akio; Yamamoto, Hideki

2018-03-01

La2-xSrxCuO4 (LSCO) and La2-xBaxCuO4 (LBCO) have been recognized as the archetype materials of "hole-doped" high-Tc superconductors. Their crystal structures are relatively simple with a small number of constituent cation elements. In addition, the doping level can be varied by the chemical substitution over a wide range enough to obtain the full spectrum of doping-dependent electronic and magnetic properties. These attractive features have dedicated many researchers to thin-film growth of LSCO and LBCO. The critical temperature (Tc) of LSCO and LBCO is sensitive to strain as manifested by a positive pressure coefficient of Tc in bulk samples. In general, films are strained if they are grown on lattice-mismatched substrates (epitaxial strain). Early attempts (before 1997) at the growth of LSCO and LBCO films resulted in depressed Tc below 30 K as they were grown on a commonly used SrTiO3 substrate (in-plane lattice parameter asub = 3.905 Å): the in-plane lattice parameters of LSCO and LBCO are ≤3.80 Å, and hence tensile epitaxial strain is introduced. The situation was changed by the use of LaSrAlO4 substrates with a slightly shorter in-plane lattice constant (asub = 3.756 Å). On LaSrAlO4 substrates, the Tc reaches 45 K in La1.85Sr0.15CuO4, 47 K in La1.85Ba0.15CuO4, and 56 K in ozone-oxidized La2CuO4+δ films, substantially higher than the Tc's of the bulk compounds. The Tc increase in La1.85Sr0.15CuO4 films on LaSrAlO4 and decrease on SrTiO3 are semi-quantitatively in accord with the phenomenological estimations based on the anisotropic strain coefficients of Tc (dTc/dεi). In this review article, we describe the growth and properties of films of cuprates having the K2NiF4 structure, mainly focusing on the increase/decrease of Tc by epitaxial strain and quasi-stable phase formation by epitaxial stabilization. We further extract the structural and/or physical parameters controlling Tc toward microscopic understanding of the variation of Tc by epitaxial strain.

Evidence for anisotropic excitonlike enhancement of the Raman scattering from La2CuO4

International Nuclear Information System (INIS)

Weber, W.H.; Peters, C.R.; Wanklyn, B.M.; Chen, C.; Watts, B.E.

1988-01-01

Polarized Raman studies on oriented single crystals of La 2 CuO 4 yield α/sub z//sub z/ spectra with narrow lines at 429 and 228 cm/sup -1/ that are identified as the two A 1 /sub g/ modes expected for the tetragonal K 2 NiF 4 structure; α/sub x//sub z/ spectra with one line at 228 cm/sup -1/ that has E/sub g/ symmetry; and α/sub x//sub x/ spectra with numerous peaks that are due to normally forbidden phonon excitations. The α/sub x//sub x/ spectra also show strong second-order features, suggesting a highly anisotropic, excitonlike enhancement of the Raman scattering

Synthesis and characterization of binary (CuO)0.6(CeO2)0.4 nanoparticles via a simple heat treatment method

Science.gov (United States)

Baqer, Anwar Ali; Matori, Khamirul Amin; Al-Hada, Naif Mohammed; Shaari, Abdul Halim; Kamari, Halimah Mohamed; Saion, Elias; Chyi, Josephine Liew Ying; Abdullah, Che Azurahanim Che

2018-06-01

A binary (CuO)0.6 (CeO2)0.4 nanoparticles were prepared via thermal treatment method, using copper nitrate, cerium nitrate as precursors, PVP as capping agent and de-ionized water as a solvent. The structures, morphology, composition of the element and optical properties of these nanoparticles have been studied under different temperatures using various techniques. The XRD spectrum of the samples at 500 °C and above confirmed the existence of both monoclinic (CuO) and cubic fluorite (CeO2) structures. The findings of FESEM and TEM exhibited the average practical size and agglomeration increment with an elevation in the calcination temperature. The synthesized nanoparticles were also characterized by FTIR, which indicated the formation of binary Cu-O and Ce-O bonds. The EDX analysis was performed to indicate the chemical composition of the sample. The double energy band gaps of (CuO)0.6(CeO2)0.4 reduction with rising calcination temperature, can be referred to the enhancement of the crystallinity of the samples. PL intensity of (CuO)0.6(CeO2)0.4 nanoparticles peaks, which increased with the elevation of the calcination temperature to 800 °C was observed from the PL spectrum; this was due to the increment of the particle size that occurred.

Local structure and superconductivity in La2-xBaxCuO4 for x=0.125 and x=0.15

International Nuclear Information System (INIS)

Billinge, S.J.L.; Kwei, G.H.; Takagi, H.

1993-01-01

This paper reviews our recent work on characterising the structural and electronic transitions in La 2-x Ba x CuO 4 . This is a high-temperature superconductor which shows interesting an interesting interrelationship between structure and atomic properties. We have used x-ray and neutron diffraction to characterize the structure and show tat the current understanding of the structural phase transitions, and their relationship to the superconductivity, is incomplete

Five-fold way to new high Tc superconductors

Indian Academy of Sciences (India)

Discovery of high c superconductivity in La2−BaCuO4 by Bednorz and Muller in 1986 was a breakthrough in the 75-year long search for new superconductors. Since then new high c superconductors, not involving copper, have also been discovered. Superconductivity in cuprates also inspired resonating valence ...

Tricrystal tunneling evidence for d-wave pairing symmetry in cuprate superconductors

International Nuclear Information System (INIS)

Tsuei, C.C.; Kirtley, J.R.

1997-01-01

Strong evidence for d-wave pairing symmetry in high-temperature superconductors such as YBa 2 Cu 3 O 7 and Tl 2 Ba 2 CuO 6+δ has been obtained by monitoring the presence or absence of the half-integer flux quantum effect in various controlled - orientation tricrystal superconducting systems. New results of a tricrystal tunneling experiment with Gd Ba 2 Cu 3 O 7 will also be presented. (orig.)

Superconductor-semiconductor-superconductor planar junctions of aluminium on DELTA-doped gallium arsenide

DEFF Research Database (Denmark)

Taboryski, Rafael Jozef; Clausen, Thomas; Kutchinsky, jonatan

1997-01-01

We have fabricated and characterized planar superconductor-semiconductor-superconductor (S-Sm-S) junctions with a high quality (i.e. low barrier) interface between an n++ modulation doped conduction layer in MBE grown GaAs and in situ deposited Al electrodes. The Schottky barrier at the S...

Synthesis, structural and physico-chemical studies of the monocrystal superconductor oxides Hg Ba{sub 2} Ca{sub n-1} Cu{sub n} O{sub 2n+2+{delta}}; Synthese, etudes structurales et physico-chimiques de monocristaux d`oxydes supraconducteurs Hg Ba{sub 2} Ca{sub n-1} Cu{sub n} O{sub 2n+2+{delta}}

Energy Technology Data Exchange (ETDEWEB)

Viallet-Guillen, Virginie [Dept. de Recherche sur l` Etat Condense, CEA Centre d` Etudes de Saclay, 91 - Gif-sur-Yvette (France)

1998-01-01

The thesis presents the synthesis and the structural and physico-chemical properties of the mercury-based monocrystal superconductor oxides. The results reported in the first chapter refer to the first three members of the mercury cuprate series Hg-1201, Hg-1212 and Hg-1223. In the second chapter detailed results concerning the structure of these compounds are given highlighting the features common to all cuprates and pointing out the peculiarities of mercury phases. The third chapter presents the phase diagrams ({delta}, T, p(O{sub 2})) of the compounds HgBa{sub 2}CuO{sub 4+{delta}} and HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+{delta}} obtained by thermogravimetry under controlled atmosphere between 150 deg.C and 500 deg.C and thermodynamic equilibrium conditions. In the case of Hg-1201, the critical temperature shows a variation close to a parabolic law, with an optimal Tc of 96 K ({delta}{approx_equal}0.10) while in Hg-1223 the Tc increases linearly with the O content up to the optimal Tc of 135 K ({delta}{approx_equal}0.19) and decreases only by 2 K in the over-doped regime. Finally, in the fourth chapter different physical properties are reviewed. The obtained monocrystals allowed studying the resistive transitory anisotropy, the torque, the specific heat, the nuclear magnetic resonance and the Raman diffusion 212 refs., 106 figs., 30 tabs.

Theory of terahertz electric oscillations by supercooled superconductors

Energy Technology Data Exchange (ETDEWEB)

Mishonov, Todor M; Mishonov, Mihail T [Department of Theoretical Physics, Faculty of Physics, University of Sofia St Kliment Ohridski, 5 J Bourchier Boulevard, 1164 Sofia (Bulgaria); Laboratorium voor Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200 D B-3001 Leuven (Belgium)

2005-11-15

We predict that below T{sub c} a regime of negative differential conductivity (NDC) can be reached. The superconductor should be supercooled to Tsuperconductor is created by the excess conductivity of the fluctuation Cooper pairs. We propose NDC of supercooled superconductors to be used as an active medium for generation of electric oscillations. Such generators can be used in the superconducting electronics as a new type THz source of radiation. Oscillations can be modulated by the change of the bias voltage, electrostatic doping by a gate electrode when the superconductor is the channel of a field effect transistor, or by light. When small amplitude oscillations are stabilized near the critical temperature T{sub c} the generator can be used as a bolometer. NDC, which is essential for the applications, is predicted on the basis of analysis of known results for fluctuation conductivity, obtained in previous papers by solving the Boltzmann kinetic equation for the Cooper pairs metastable in the normal phase. The Boltzmann equation for fluctuation Cooper pairs is a result of state-of-the-art application of the microscopic theory of superconductivity. Our theoretical conclusions are based on some approximations like time dependent Ginzburg-Landau theory initially derived for gapless superconductors, but nevertheless can reliably predict the appearance of NDC. NDC is the main ingredient of the proposed technical applications. The maximal frequency at which superconductors can operate as generators is determined by the critical temperature {Dirac_h}/2{pi}{omega}{sub max} {approx} k{sub B}T{sub c}. For high-T{sub c} superconductors this maximal frequency falls well inside the terahertz range. Technical conditions to avoid nucleation of the superconducting phase are briefly discussed. We suggest that nanostructured high-T{sub c} superconductors patterned in a single chip can

Neutron diffraction studies of high-T/sub c/ superconductors

International Nuclear Information System (INIS)

Jorgensen, J.D.

1988-03-01

Neutron powder diffraction techniques have been used extensively for the study of high-T/sub c/ oxide superconductors because of the need to locate oxygen atoms and accurately determine the oxygen site occupancies, and the difficulty in obtaining single crystals. For example, in the case of YBa 2 Cu 3 O/sub 7-δ/, neutron powder diffraction and Rietveld structural refinement were used to obtain the first complete structural information. Subsequent experiments focussed on determining the relationship of superconducting properties to the number and distribution of oxygen vacancies on the Cu-O sublattice with measurements being done on samples in thermodynamic equilibrium, at high temperature in controlled oxygen atmospheres, and on metastable, oxygen-deficient samples produced by quenching. Neutron powder diffraction has also been used to determine the structures of compounds in which the properties have been modified by substitution on the Y, Ba, or Cu sites. This paper briefly reviews some of the neutron powder diffraction results in these areas. 17 refs

Promoting Ethylene Selectivity from CO2 Electroreduction on CuO Supported onto CO2 Capture Materials.

Science.gov (United States)

Yang, Hui-Juan; Yang, Hong; Hong, Yu-Hao; Zhang, Peng-Yang; Wang, Tao; Chen, Li-Na; Zhang, Feng-Yang; Wu, Qi-Hui; Tian, Na; Zhou, Zhi-You; Sun, Shi-Gang

2018-03-09

Cu is a unique catalyst for CO 2 electroreduction, since it can catalyze CO 2 reduction to a series of hydrocarbons, alcohols, and carboxylic acids. Nevertheless, such Cu catalysts suffer from poor selectivity. High pressure of CO 2 is considered to facilitate the activity and selectivity of CO 2 reduction. Herein, a new strategy is presented for CO 2 reduction with improved C 2 H 4 selectivity on a Cu catalyst by using CO 2 capture materials as the support at ambient pressure. N-doped carbon (N x C) was synthesized through high-temperature carbonization of melamine and l-lysine. We observed that the CO 2 uptake capacity of N x C depends on both the microporous area and the content of pyridinic N species, which can be controlled by the carbonization temperature (600-800 °C). The as-prepared CuO/N x C catalysts exhibit a considerably higher C 2 H 4 faradaic efficiency (36 %) than CuO supported on XC-72 carbon black (19 %), or unsupported CuO (20 %). Moreover, there is a good linear relationship between the C 2 H 4 faradaic efficiency and CO 2 uptake capacity of the supports for CuO. The local high CO 2 concentration near Cu catalysts, created by CO 2 capture materials, was proposed to increase the coverage of CO intermediate, which is favorable for the coupling of two CO units in the formation of C 2 H 4 . This study demonstrates that pairing Cu catalysts with CO 2 capture supports is a promising approach for designing highly effective CO 2 reduction electrocatalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of gases by a pulsed voltammetric sensor and the electrochemistry of high T[sub c] superconductors

Energy Technology Data Exchange (ETDEWEB)

Rochani, S.

1991-01-01

This thesis is presented in two parts: Studies of gas sensing probes and the electrochemistry of superconductors. A Clark type polarographic oxygen sensor was used to analyze oxygen, hydrogen, chlorine, sulphur dioxide and nitrogen dioxide. A pulsed potential was applied driven by an IBM/XT compatible microcomputer with a 12 bit A-D/D-A card. In a series of experiments for each gas singly, and then mixtures, the probe was calibrated at different concentrations of gas dissolved in water at different times during the pulse to observe the optimum measurement. In the case of oxygen for a 20 s pulse at [minus]0.65 V between a platinum and silver/silver chloride, the optimum calibration was obtained between 2 and 4 s with a detection limit of 0.27 ppm oxygen. Hydrogen was determined at +0.60 V with a 50 s pulse and optimum range 3 to 4 s and detection limit 0.02 ppm. Chlorine was reduced at 0 V and optimally detected after 2 s of a 20 s pulse with a detection limit of 3 ppm. A mixture of hydrogen and oxygen was analyzed without mutual interference by a train of pulses at [minus]0.65, 0, +0.60 V or [minus]0.65, +0.60 V. For sulphur dioxide, a new probe was constructed with a separate reference, working and auxillary electrodes to overcome the formation of silver sulphide at the auxillary electrode. A preliminary study of nitrogen dioxide was done by observing the oxidation and reduction current at different applied voltages. Samples of each of the room temperature superconductors YBa[sub 2]Cu[sub 3]O[sub 7[minus][sigma

The influence of fluorine on the structures and properties of Pr sub 2 sub - sub x Sr sub x CuO sub 4 sub - sub y (x = 0.0, 0.4, 1.0)

CERN Document Server

Yang Jin Ling; Tang Wei Hua; Rao Guang Hui; Liang Jing Kui; Jin Duo

1997-01-01

Introducing F into the lattices of the copper oxides Pr sub 2 CuO sub 4 , Pr sub 1 sub . sub 6 Sr sub 0 sub . sub 4 CuO sub 4 and PrSrCuO sub 4 sub - sub y is accomplished via a low-temperature fluorination reaction using CuF sub 2 as the fluorinating reagent. The oxyfluorides retain the structures of their precursors, but striking lattice expansions are observed. No trace of SrF sub 2 was detected in the fluorinated products. F doping was successfully used to induce superconductivity in the oxyfluoride PrSrCu(O, F) sub 4 sub - subdelta (T sub c = 15 K) with a reduced CuO sub 2 plane and in the presence of apical anions, but failed to optimize the carrier density and induce superconductivity in Pr sub 2 CuO sub 4 sub - sub x F sub x and Pr sub 1 sub . sub 6 Sr sub 0 sub . sub 4 CuO sub 4 sub - sub x F sub x. (author)

Potential aerospace applications of high temperature superconductors

Science.gov (United States)

Selim, Raouf

1994-01-01

The recent discovery of High Temperature Superconductors (HTS) with superconducting transition temperature, T(sub c), above the boiling point of liquid nitrogen has opened the door for using these materials in new and practical applications. These materials have zero resistance to electric current, have the capability of carrying large currents and as such have the potential to be used in high magnetic field applications. One of the space applications that can use superconductors is electromagnetic launch of payloads to low-earth-orbit. An electromagnetic gun-type launcher can be used in small payload systems that are launched at very high velocity, while sled-type magnetically levitated launcher can be used to launch larger payloads at smaller velocities. Both types of launchers are being studied by NASA and the aerospace industry. The use of superconductors will be essential in any of these types of launchers in order to produce the large magnetic fields required to obtain large thrust forces. Low Temperature Superconductor (LTS) technology is mature enough and can be easily integrated in such systems. As for the HTS, many leading companies are currently producing HTS coils and magnets that potentially can be mass-produced for these launchers. It seems that designing and building a small-scale electromagnetic launcher is the next logical step toward seriously considering this method for launching payloads into low-earth-orbit. A second potential application is the use of HTS to build sensitive portable devices for the use in Non Destructive Evaluation (NDE). Superconducting Quantum Interference Devices (SQUID's) are the most sensitive instruments for measuring changes in magnetic flux. By using HTS in SQUID's, one will be able to design a portable unit that uses liquid nitrogen or a cryocooler pump to explore the use of gradiometers or magnetometers to detect deep cracks or corrosion in structures. A third use is the replacement of Infra-Red (IR) sensor leads on

Point-contact electron tunneling into the high-Tc superconductor Y-Ba-Cu-O

Science.gov (United States)

Kirk, M. D.; Smith, D. P. E.; Mitzi, D. B.; Sun, J. Z.; Webb, D. J.

1987-06-01

Results are reported from a study of electron tunneling into bulk samples of the new high-Tc superconductor Y-Ba-Cu-O using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 2Delta = 100 MeV), implying 2Delta/kBTc = about 13. Similar values were found for La-Sr-Cu-O. The structure in the I-V curves is also similar to that seen in La-Sr-Cu-O. From the asymmetries observed in the I-V characteristics, it is inferred that the natural tunneling barrier on this material is of the Schottky type.

Doping effects in high-Tc superconductors

International Nuclear Information System (INIS)

Hessel Andersen, N.

1996-11-01

The purpose of the project has been to study how the superconducting and magnetic properties of the high temperature superconductors change as function of oxygen stoichiometry and cation doping. The primary system of investigation has been YBa 2 Cu 3 O 6+x , which has been studied as function of oxygen stoichiometry, 0 2 planes, that is necessary for superconductivity, is strongly depending on structural ordering. The static properties and the kinetics of the structural ordering process have been studied experimentally by neutron and high energy synchrotron x-ray diffraction, by Raman scattering, and by computer simulation technique. Not only the oxygen stoichiometry but also the cation doping has been shown to influence the magnetic phases, in some cases in an unexpected manner. Thus, by neutron diffraction experiments it has been shown that doping with non-magnetic Al gives rise to a new magnetic phase. A theoretical model, has been developed. The magnetic phases of the Cu and Nd ordering in NdBa 2 Cu 3 O 6+x , and of the Cu and Pr ordering in PrBa 2 Cu 3 O 6+x have been studied by neutron diffraction with the main purpose of understanding why PrBa 2 Cu 3 O 6+x is magnetic and non-superconducting for all oxygen stoichiometries. In NdBa:2Cu 3 O 6+x studies of the magnetic flux lattice have been carried out by Small Angle Neutron Scattering. Additional structural studies of the superconducting and magnetic phases of related materials, of RENi 2 B 2 C (RE = rare earth), and of oxidized and cation doped materials based on La 2 CuO 4+δ have been carried out. Methods for structural studies and analyses, and equipment for electrical and magnetic characterization have been developed. (EG) 5 tabs., 46 ills., 35 refs

Ultra-fine CuO Nanoparticles Embedded in Three-dimensional Graphene Network Nano-structure for High-performance Flexible Supercapacitors

International Nuclear Information System (INIS)

Li, Yanrong; Wang, Xue; Yang, Qi; Javed, Muhammad Sufyan; Liu, Qipeng; Xu, Weina; Hu, Chenguo; Wei, Dapeng

2017-01-01

High conductivity, large specific surface area and excellent performance redox materials are urgently desired for improving electrochemical energy storage. However, with single redox material it is hard to achieve these properties. Herein, we develop ultra-fine CuO nanoparticles embedded in three-dimensional graphene network grown on carbon cloth (CuO/3DGN/CC) to construct a novel electrode material with advantages of high conductivity, large specific area and excellent redox activity for supercapacitor application. The CuO/3DGN/CC with different CuO mass ratios are utilized to fabricate supercapacitors and the optimized mass loading achieves the high areal capacitance of 2787 mF cm"−"2 and specific capacitance of 1539.8 F g"−"1 at current density of 6 mA cm"−"2 with good stability. In addition, a high-flexible solid-state symmetric supercapacitor is also fabricated by using this CuO/3DGN/CC composite. The device shows excellent electrochemical performance even at various bending angles indicating a promising application for wearable electronic devices, and two devices with area 2 × 4 cm"2 in series can light nine light emitting diodes for more than 3 minutes.

Simulation of high field induced first-order phase transition in Bi2Sr2CaCu2O8

International Nuclear Information System (INIS)

Viana, Leonardo P.; Raposo, E.P.; Coutinho-Filho, M.D.

2004-01-01

The occurrence and nature of first-order transitions (FOT) in Bi 2 Sr 2 CaCu 2 O 8 (BSCCO) are still open issues, although results from a number of experiments do support a FOT both at low and high fields. We present a FOT obtained via Monte Carlo simulations using the Lawrence-Doniach model for layered superconductors, focusing on a clean 3D sample of BSCCO, with dc field applied perpendicular to the CuO 2 planes. Our results confirm Nelson's predictions for the random-walk-like diffusion of melted lines, contrarily to some recent suggestions. Further results for the z-dependent density-density correlation function indicate that in the high field regime the CuO 2 planes decouple along with line melting, in agreement with experimental observations in BSCCO

Heteroepitaxial growth of strained multilayer thin films of high-temperature superconductors

International Nuclear Information System (INIS)

Gross, R.; Gupta, A.; Olsson, E.; Segmueller, A.; Koren, G.

1991-01-01

Recently, the heteroepitaxial growth of multilayer structures of different copper oxide superconductors has been reported by several groups. In general, two different types of multilayer structures should be distinguished. The first kind of mulitlayer is formed by high-T c materials having the same crystal structure and almost the same lattice constants, as for example ReBa 2 Cu 3 O 7 (Re=rare earth) multilayers with alternating Re-elements. In these multilayers the two different rare earth copper oxides (Y/Dy, Y/Pr) have the same orthorhombic unit cell. Due to the very similar lattice constants, the misfit strain is easily accommodated without the formation of defects. The second kind of multilayer is formed by layers of materials having different crystal structure and lattice parameters. In these multilayers the misfit can be coherently accommodated below a critical modulation thickness as discussed below. This renders possible the heteroepitaxial growth of strained multilayer structures, both of two copper oxides of different crystal structure, as has been demonstrated recently for the system YBa 2 Cu 3 O 7-δ /Nd 1.83 Ce 0.17 CuO x , and of superconducting copper oxides and insulating materials. For multilayers of different copper oxides, a combination of almost all high-Tc materials should be possible, since the presence of the CuO 2 sheets in these materials results in similar lattice constants in their basal planes ('a' and 'b'). (orig./BHO)

Critical parameters in the sputter-deposition of NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thin films

Energy Technology Data Exchange (ETDEWEB)

Hakuraku, Y.; Yokoyama, N.; Doi, T.; Inoue, T. [Faculty of Engineering, Kagoshima University, Koorimoto, Kagoshima 890, (Japan); Mori, Z.; Koba, S. [Yatsushiro National College of Technology, Yatsushiro 866 (Japan)

1999-08-01

A superconducting thin film of NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NBCO) was prepared on an MgO(100) substrate by dc magnetron sputtering. Superconducting properties as well as features such as resistivity at room temperature and surface morphology were improved by optimizing the composition of sputtering target and critical parameters such as substrate temperature and oxidation gas pressure. A highly c-axis oriented thin film with T{sub c} (zero resistance temperature) = 95.2 K was obtained reproducibly with NdBa{sub 2}Cu{sub 3.2}O{sub 7-{delta}} off-stoichiometric target sputtering. T{sub c} = 95.2 K was 8 K higher than that deposited by stoichiometric target sputtering. Critical current density was 1x10{sup 6} A cm{sup -2} at 77 K, and surface roughness was 35 nm. (author)

Quantitative XPS analysis of high Tc superconductor surfaces

International Nuclear Information System (INIS)

Jablonski, A.; Sanada, N.; Suzuki, Y.; Fukuda, Y.; Nagoshi, M.

1993-01-01

The procedure of quantitative XPS analysis involving the relative sensitivity factors is most convenient to apply to high T c superconductor surfaces because this procedure does not require standards. However, a considerable limitation of such an approach is its relatively low accuracy. In the present work, a proposition is made to use for this purpose a modification of the relative sensitivity factor approach accounting for the matrix and the instrumental effects. The accuracy of this modification when applied to the binary metal alloys is 2% or better. A quantitative XPS analysis was made for surfaces of the compounds Bi 2 Sr 2 CuO 6 , Bi 2 Sr 2 CaCu 2 O 8 , and YBa 2 Cu 3 O Y . The surface composition determined for the polycrystalline samples corresponds reasonably well to the bulk stoichiometry. Slight deficiency of oxygen was found for the Bi-based compounds. The surface exposed on cleavage of the Bi 2 Sr 2 CaCu 2 O 8 single crystal was found to be enriched with bismuth, which indicates that the cleavage occurs along the BiO planes. This result is in agreement with the STM studies published in the literature

Positron annihilation in Bi1.8Sb0.2Sr2Ca2Cu3Ox superconductor

International Nuclear Information System (INIS)

Chen Feng; Zheng Shennan; Zhang Suqun

1992-01-01

The positron lifetime and Doppler broadening line-shape parameter are measured as a function of the temperature from 78 K to 300 K for the Bi 1.8 Sb 0.2 Sr 2 Ca 2 Cu 3 O x superconductor. A decrease of both lifetime and S parameter is observed across T c . This can be interpreted by the theory of local charge transferring from the CuO layer to the BiO layer during superconducting transition. In the temperature region of normal state two anomalies are found around 165 K and 235 K. The possible origin of the observed anomalies is discussed

Systematics of c-axis phonons in the thallium- and bismuth-based cuprate superconductors

NARCIS (Netherlands)

Tsvetkov, A.A.; Dulic, Diana; Marel, D. van der; Damascelli, A.; Kaljushnaia, G.A.; Gorina, J.I.; Senturina, N.N.; Kolesnikov, N.N.; Ren, Z.F.; Wang, J.H.; Menovsky, A.A.; Palstra, T.T.M.

1999-01-01

We present grazing incidence reflectivity measurements in the far-infrared region at temperatures above and below Tc for a series of thallium- (Tl2Ba2CuO6, Tl2Ba2CaCu2O8) and bismuth- (Bi2Sr2CuO6, Bi2Sr2CaCu2O8, and Bi2-xPbxSr2CaCu2O8) based cuprate superconductors. From the spectra, which are

Anisotropy effects in superconductors with magnetic impurities. Pt. 2

International Nuclear Information System (INIS)

Entel, P.

1976-01-01

The influence of Fermi surface anisotropy on the specific heat jumps, ΔC, at the phase transition for superconductors containing magnetic and nonmagnetic impurities is discussed. In the framework of a simple two-band or two-zone model we find for small interband electron-phonon coupling constants characteristic maxima in the ΔC(Tsub(c))-curve. These departures from the corresponding ΔC-curve of a single-band isotropic superconductor are mostly pronounced for weak and strong interband Coulomb scattering of conduction electrons on nonmagnetic ions. There is only a small range of intermediate scattering rates for which the maxima are smeared out. (orig.) [de

Phonon characteristics of high Tc superconductors from neutron Doppler broadening measurements

International Nuclear Information System (INIS)

Trela, W.J.; Kwei, G.H.; Lynn, J.E.; Meggers, K.

1994-01-01

Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La 2-x Ba x CuO 4 . Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra

Superconductivity in copper-oxygen compounds

Energy Technology Data Exchange (ETDEWEB)

Hackl, Rudi [Walther-Meissner-Inst. der Bayerischen Akademie der Wissenschaften, Muenchen (Germany)

2011-07-01

The discovery of superconductors on copper-oxygen basis in 1986 was one of the most celebrated events in condensed matter physics. The maximal transition temperature T{sub c} close to 150 K was observed in HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+{delta}} at high pressure. In spite of enormous progress in both the experimental knowledge and theoretical understanding, the origin of the high T{sub c} remains elusive. Although the materials properties require unexpectedly complicated technical solutions several applications have been commercialized. (orig.)

CuO cauliflowers for supercapacitor application: Novel potentiodynamic deposition

International Nuclear Information System (INIS)

Dubal, Deepak P.; Gund, Girish S.; Lokhande, Chandrakant D.; Holze, Rudolf

2013-01-01

Graphical abstract: Schematic experimental setup used for the potentiodynamic mode of electrodeposition for the synthesis of CuO cauliflower onto stainless steel substrate. Highlights: ► Synthesis of CuO using potentiodynamic mode of electrodeposition. ► Uniformly spread cauliflower-like nanostructure. ► CuO cauliflowers provide high specific capacitance with good stability. ► CuO cauliflowers show high power and energy density values. -- Abstract: In present investigation, synthesis and characterization of novel cauliflower-like copper oxide (CuO) and its electrochemical properties have been performed. The utilized CuO cauliflowers were prepared by potentiodyanamic mode from an aqueous alkaline bath. X-ray diffraction pattern confirm the formation of monoclinic CuO cauliflowers. Scanning electron micrograph analysis reveals that CuO cauliflowers are uniformly spread all over the substrate surface with the surface area of 49 m 2 g −1 with bimodal pore size distribution. Electrochemical analysis shows that CuO cauliflower exhibits high specific capacitance of 179 Fg −1 in 1 M Na 2 SO 4 electrolyte with 81% capacity retention after 2000 cycles. The Ragone plot discovers better power and energy densities of cauliflowers-like CuO sample. Present investigation illustrates that the potentiodynamic approach for the direct growth of cauliflower-like CuO is simple and cost-effective and can be applied for synthesis of other metal oxides, polymers etc.

A study of lattice dynamics in iron-based superconductors by inelastic light scattering

Energy Technology Data Exchange (ETDEWEB)

Um, Youngje

2013-12-13

After the discovery of high temperature (high T{sub c}) superconductivity in copper oxide-based materials (cuprates) in 1986, this phenomenon was a unique property of the cuprates for more than 20 years. The origin of high T{sub c} superconductivity is still under debate. In 2008, high T{sub c} superconductivity was discovered in iron-based compounds. This discovery presents new opportunities for the development of a fundamental understanding of high T{sub c} superconductivity. Density functional calculations indicate a weak electron-phonon coupling strength in iron-based superconductors and these suggest that superconductivity is not mediated by phonons. However, experimental report of a large isotope effect of the iron atoms on the superconductivity T{sub c} suggests that phonons play an important role in iron-based superconductors. Motivated by these findings, this thesis presents a Raman scattering study of the lattice dynamics of the iron-based superconductors Fe{sub 1+y}Te{sub 1-x}Se{sub x}, LiFeAs and NaFe{sub 1-x}Co{sub x}As as a function of chemical composition and temperature. In Fe{sub 1+y}Te{sub 1-x}Se{sub x}, an unconventional linewidth broadening of the c-axis polarized Fe phonon of B{sub 1g} symmetry is found with decreasing temperature, which indicates an unusual coupling between the phonon and iron excessinduced magnetic fluctuations in this compound. In LiFeAs, the Raman scattering data provide evidence for a weak electron-phonon coupling, which is consistent with non-phonon mediated Cooper pairing in this compound. In NaFe{sub 1-x}Co{sub x}As, upon cooling two features are observed: (i) an unconventional linewidth broadening of several phonons, which is indicative of spin fluctuation-phonon coupling, and (ii) a superconductivity-induced phonon lineshape renormalization, which can not be explained by standard model calculations.

Indides RE{sub 3}T{sub 2}In{sub 4} (RE = Y, Gd-Tm, Lu; T = Ni, Ru, Rh) with a ZrNiAl superstructure

Energy Technology Data Exchange (ETDEWEB)

Heying, Birgit; Niehaus, Oliver; Rodewald, Ute C.; Poettgen, Rainer [Univ. Muenster (Germany). Inst. fuer Anorganische und Analytische Chemie

2016-07-01

Three series of rare earth-transition metal-indides RE{sub 3}T{sub 2}In{sub 4} (RE=Y, Gd-Tm, Lu; T=Ni, Ru, Rh) were synthesized from arc-melted RE{sub 3}T{sub 2} precursor compounds and indium tear shot in sealed niobium ampoules using different annealing sequences. The new indides crystallize with the hexagonal Lu{sub 3}Co{sub 2}In{sub 4}-type structure, space group P anti 6. All samples were characterized on the basis of Guinier powder patterns and six structures were refined from single crystal X-ray diffractometer data. The RE{sub 3}T{sub 2}In{sub 4} structures are derived from the ZrNiAl type through RE/In ordering, paralleled by a symmetry reduction from P anti 62m to P anti 6. This induces twinning for some of the investigated crystals. The main crystal chemical motifs of the RE{sub 3}T{sub 2}In{sub 4} structures are trigonal prisms of rare earth, respectively indium atoms that are filled by the transition metals.

Temperature and depth dependence of positron annihilation parameters in YBa2Cu3O/sub 7-x/ and La/sub 1.85/Sr/sub 0.15/CuO4

International Nuclear Information System (INIS)

Lynn, K.G.; Usmar, S.G.; Nielsen, B.; van der Kolk, G.; Kanazawa, I.; Sferlazzo, P.; Moodenbaugh, A.R.

1988-01-01

The temperature dependence of the positron annihilation parameters for YBa 2 Cu 3 O/sub 7-//sub x/ x = 0.7, 0.4 and 0.0 and La/sub 1.85/Sr/sub 0.15/CuO 4 were measured. The depth dependence of the YBa 2 Cu 3 O 7 was studied using a variable-energy positron beam showing a strong depth dependence in the Doppler line-shape extending up to an average depth of ∼5.0 μm. It was found that a transition in the Doppler line-shape parameter, ''S'', was associated with the superconducting transition temperature (T/sub c/) in YBa 2 Cu 3 O/sub 7-x/ x = 0.4 and 0.0 while no transition was observed in the nonsuperconducting YBa 2 Cu 3 O/sub 6.3/. Positron lifetime parameters in YBa 2 Cu 3 O 7 were found to be consistent with positrons localized at open volume regions (probably unoccupied crystallographic sites) in this material with a lifetime of 210 psec at 300 K. These results indicate that the electron density at these unoccupied sites increases, using a free electron model, approximately 9% between 100 and 12 K

Role of apical oxygen in 2-1-4 electron-doped superconductors

Czech Academy of Sciences Publication Activity Database

Richard, P.; Riou, G.; Jandl, S.; Poirier, M.; Furnier, P.; Nekvasil, Vladimír; Diviš, M.

408-410, - (2004), s. 830-831 ISSN 0921-4534 R&D Projects: GA ČR GA202/03/0552 Institutional research plan: CEZ:AV0Z1010914 Keywords : Nd 2-x Ce x CuO 4 * crystal-field * apical oxygen * HTSC Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.072, year: 2004

Structural study of Sr{sub 2}CuO{sub 3+delta} by neutron powder diffraction

Energy Technology Data Exchange (ETDEWEB)

Shimakawa, Y. [NEC Corp., Tsukuba (Japan). Fundamental Research Labs.; Jorgensen, J.D.; Mitchell, J.F.; Hunter, B.A. [Argonne National Lab., IL (United States); Shaked, S. [Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev][Ben-Gurion Univ. of the Negev, Beersheba (Israel). Dept. of Physics; Hinks, D.G.; Hitterman, R.L. [Argonne National Lab., IL (United States); Hiroi, Z.; Takano, M. [Kyoto Univ., Uji (Japan). Inst. for Chemical Research

1996-11-01

Average crystal structures of superconducting Sr{sub 2}CuO{sub 3+{delta}} synthesized at ambient pressure from a hydroxometallate precursor were refined from neutron powder diffraction data. A simplified model was used to fit the modulated superstructures. Both compounds have an oxygen deficient La{sub 2}CuO{sub 4}-type tetragonal T structure with O vacancies located in the CuO{sub 2} planes, not in the Sr{sub 2}O{sub 2} layers. This raises important questions about the superconductivity in Sr{sub 2}CuO{sub 3+{delta}} reported to be a 70 K superconductor.

Images of interlayer Josephson vortices in single-layer cuprates

International Nuclear Information System (INIS)

Moler, K. A.; Kirtley, J. R.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Williams, J. M.; Schlueter, J. A.; Hinks, D.; Villard, G.; Maignan, A.; Nohara, M.; Takagi, H.

2000-01-01

The interlayer penetration depth in layered superconductors may be determined from scanning Superconducting QUantum Interference Device (SQUID) microscope images of interlayer Josephson vortices. The authors compare their findings at 4 K for single crystals of the organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 and three near-optimally doped cuprate superconductors: La 2-x Sr x CuO 4 , (Hg, Cu)Ba 2 CuO 4+δ , and Tl 2 Ba 2 CuO 6+δ

Electronic properites of electron-doped cuprate superconductors probed by high-field magnetotransport

International Nuclear Information System (INIS)

Helm, Toni

2013-01-01

In the present work the normal-state properties of the electron-doped cuprate superconductor Nd 2-x Ce x CuO 4 (NCCO) are investigated for a broad doping range, covering almost the whole phase diagram of this material. Magnetotransport measurements in the world's highest non-destructive magnetic fields were used as a spectroscopic tool for probing the electronic structure of single-crystalline NCCO as a function of the carrier concentration x. Quantum and semiclassical oscillations in the magnetoresistance provided new insights into various properties of the Fermi surface and the nature of the ground state in the system. The detailed investigations of the field- and temperature-dependent transport and its dependence on the field orientation have revealed a close correlation between symmetry-breaking ordering instabilities and the superconducting state.

Superconducting materials

International Nuclear Information System (INIS)

Ruvalds, J.

1990-01-01

This report discusses the following topics: Fermi liquid nesting in high temperature superconductors; optical properties of high temperature superconductors; Hall effect in superconducting La 2-x Sr x CuO 4 ; source of high transition temperatures; and prospects for new superconductors

Azide-Alkyne Huisgen [3+2] Cycloaddition Using CuO Nanoparticles

Directory of Open Access Journals (Sweden)

Hyunjoon Song

2012-11-01

Full Text Available Recent developments in the synthesis of CuO nanoparticles (NPs and their application to the [3+2] cycloaddition of azides with terminal alkynes are reviewed. With respect to the importance of click chemistry, CuO hollow NPs, CuO hollow NPs on acetylene black, water-soluble double-hydrophilic block copolymer (DHBC nanoreactors and ZnO–CuO hybrid NPs were synthesized. Non-conventional energy sources such as microwaves and ultrasound were also applied to these click reactions, and good catalytic activity with high regioselectivity was observed. CuO hollow NPs on acetylene black can be recycled nine times without any loss of activity, and water-soluble DHBC nanoreactors have been developed for an environmentally friendly process.

Microstructural investigation of RBa/sub 2/Cu/sub 3/O/sub 7-delta/ (R=Y, Gd, Nd)

Energy Technology Data Exchange (ETDEWEB)

Parent, L; Moreau, C; Noel, D; Dallaire, S; Champagne, B

1989-02-01

RBa/sub 2/Cu/sub 3/O/sub 7-delta/ perovskites, where R is Y, Gd and Nd, were synthesized using the same experimental conditions. The resistivity curves of the three compounds were similar but their microstructures were different. Secondary phases (CuO, BaCuO/sub 2/) were formed in the compounds containing Y and Gd while no such phases were detected in the Nd perovskite material. 7 refs.; 4 figs.; 1 table.

Deposition of epitaxial thin films of Nd1.85Ce0.15CuO4-y by laser ablation

International Nuclear Information System (INIS)

Gupta, A.; Koren, G.; Tsuei, C.C.; Segmuller, A.; McGuire, T.R.

1989-01-01

Thin films of the electron-doped superconductor Nd 1.85 Ce 0.15 CuO 4-y have been deposited on (100) SrTiO 3 substrates at 780 degree C using the laser ablation technique. The deposited films are very smooth and show epitaxial growth with the c axis normal to the substrate. The transport properties of the films are very sensitive to the concentration of oxygen vacancies. Films deposited and cooled in the presence of 150 mTorr O 2 exhibit localization behavior with no evidence of superconductivity down to 5 K. Superconductivity is observed on vacuum annealing the films in situ after deposition. Films with optimum concentration of oxygen vacancies show a superconducting onset temperature of 21 K and T c (R=0) of 20 K, with a critical current density of 2x10 5 A/cm 2 at 5.5 K in zero magnetic field

Tc dependence on the number of CuO2 planes in multilayered Ba2Can-1CunO2n(O, F)2 superconductors

International Nuclear Information System (INIS)

Iyo, A; Tanaka, Y; Kodama, Y; Kito, H; Tokiwa, K; Watanabe, T

2006-01-01

Multilayered cuprates of Ba 2 Ca n-1 Cu n O 2n (O, F) 2 (F-02(n-1)n) with n = 5 - 9 have been synthesized by using high pressure synthesis method in order to investigate the variation of T c . The temperature dependence of susceptibility showed that the T c (about 80 K) does not depend on n for n 5 - 9. This result can be explained using the carrier imbalance model in multilayered cuprates. Charge reservoir layers supply most of the carriers to adjacent CuO 2 planes (OP) and the OP keeps the T c constant even for large n

High T/sub c/ screen-printed YBa2Cu3O/sub 7-//sub x/ films: Effect of the substrate material

International Nuclear Information System (INIS)

Bansal, N.P.; Simons, R.N.; Farrell, D.E.

1988-01-01

Thick films of YBa 2 Cu 3 O/sub 7-//sub x/ have been deposited on highly polished alumina, magnesia spinel, nickel aluminum titanate (Ni-Al-Ti), and barium tetratitanate (Ba-Ti) substrates by the screen printing technique. They were baked at 1000 0 C for 15 min, oxygen annealed at a lower temperature, and characterized by electrical resistivity measurements, x-ray diffraction, and optical and scanning electron microscopy. Properties of the films were found to be highly sensitive to the choice of the substrate material. The film on Ba-Ti turned green after firing, due to a reaction with the substrate and were insulating. A film on Ni-Al-Ti had a T/sub c/ (onset) ∼95 K and lost 90% of its resistance by ∼75 K. However, even at 4 K it was not fully superconducting, possibly due to a reaction between the film and the substrate and interdiffusion of the reaction products. The film on alumina had T/sub c/ (onset) ∼96 K, T/sub c/ (zero) ∼66 K, and ΔT/sub c/ (10--90%) ∼10 K. Our best film was obtained on spinel and had T/sub c/ (onset) ∼94 K, zero resistance at 81 K, and a transition width (10--90%) of ∼7 K

CuO cauliflowers for supercapacitor application: Novel potentiodynamic deposition

Energy Technology Data Exchange (ETDEWEB)

Dubal, Deepak P., E-mail: deepak.dubal@chemie.tu-chemnitz.de [Technische Universität Chemnitz, Institut für Chemie, AG Elektrochemie, D-09107 Chemnitz (Germany); Gund, Girish S.; Lokhande, Chandrakant D. [Thin Film Physics Laboratory, Department of Physics, Shivaji University, Kolhapur, 416004 (M.S) (India); Holze, Rudolf, E-mail: rudolf.holze@chemie.tu-chemnitz.de [Technische Universität Chemnitz, Institut für Chemie, AG Elektrochemie, D-09107 Chemnitz (Germany)

2013-02-15

Graphical abstract: Schematic experimental setup used for the potentiodynamic mode of electrodeposition for the synthesis of CuO cauliflower onto stainless steel substrate. Highlights: ► Synthesis of CuO using potentiodynamic mode of electrodeposition. ► Uniformly spread cauliflower-like nanostructure. ► CuO cauliflowers provide high specific capacitance with good stability. ► CuO cauliflowers show high power and energy density values. -- Abstract: In present investigation, synthesis and characterization of novel cauliflower-like copper oxide (CuO) and its electrochemical properties have been performed. The utilized CuO cauliflowers were prepared by potentiodyanamic mode from an aqueous alkaline bath. X-ray diffraction pattern confirm the formation of monoclinic CuO cauliflowers. Scanning electron micrograph analysis reveals that CuO cauliflowers are uniformly spread all over the substrate surface with the surface area of 49 m{sup 2} g{sup −1} with bimodal pore size distribution. Electrochemical analysis shows that CuO cauliflower exhibits high specific capacitance of 179 Fg{sup −1} in 1 M Na{sub 2}SO{sub 4} electrolyte with 81% capacity retention after 2000 cycles. The Ragone plot discovers better power and energy densities of cauliflowers-like CuO sample. Present investigation illustrates that the potentiodynamic approach for the direct growth of cauliflower-like CuO is simple and cost-effective and can be applied for synthesis of other metal oxides, polymers etc.

Oxygen ordering in the high-T$_c$ superconductor HgBa$_2$CaCu$_2$O$_{6+\\delta}$ as revealed by perturbed angular correlation

CERN Document Server

Mendonca, Tania Melo; Haas, Heinz; Odier, Philippe; Tavares, Pedro; Silva, Manuel Ribeiro; Lopes, Armandina; Pereira, Andre; Goncalves, Joao Nuno; Amaral, Joao; Darie, Celine; Araujo, Joao Pedro

2011-01-01

Lattice sites and collective ordering of oxygen atoms in HgBa$_2$CaCu$_2$O$_{6+\\delta}$ were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at $^{199m}$Hg nuclei have been measured as functions of oxygen doping on the Hg planes, above and below T$_c$. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non-uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O$_{2\\delta}$ dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O$_{2\\delta}$ dumbbell molecules coexist with single O$_\\delta$ atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in t...

Formation of Nb3Al in powder processed Nb-Al superconductors

International Nuclear Information System (INIS)

Johnson, P.E.

1987-05-01

In high magnetic fields, the critical current density is strongly dependent on the upper critical field, which is determined primarily by the stoichiometry of the Nb 3 Al. The critical temperature (T/sub c/), like the upper critical field, is considered to be a measure of the ''intrinsic'' quality of the superconductor, indicating the stoichiometry, order, and strain. If the A15 phase is stoichiometric and well ordered, a high T/sub c/ (and high H/sub C 2 /) is expected, regardless of the volume fraction of superconductor. On the other hand, if sigma phase is present with the A15, the resultant composition gradient across the sigma-A15 interface(s) requires that some of the A15 be off-stoichiometric, and therefore that the T/sub c/ (and H/sub C 2 /) be low. Thus the extent of the A15 (Nb 3 Al) reaction and the quality of the A15 formed are interdependent. This work focuses on the factors that control the extent of Nb 3 Al formation in Nb/Al powder wires. The morphology and content of the reacted and unreacted wires are studied in optical, SEM, and TEM micrographs. Critical current density data and its dependence on processing are explained in terms of the unreacted microstructure and its effect on the extent of Nb 3 Al formation. As a method of improving the critical current density, a new variation of the conventional powder process for wire manufacturing is developed and tested

First-principles study of native defects in bulk Sm2CuO4 and its (001) surface structure

Science.gov (United States)

Zheng, Fubao; Zhang, Qinfang; Meng, Qiangqiang; Wang, Baolin; Song, Fengqi; Yunoki, Seiji; Wang, Guanghou

2018-04-01

Using the first-principles calculations based on the density functional theory, we have studied the bulk defect formation and surface structures of Sm2CuO4. To ensure the accuracy of calculations, the spin order of Cu atoms is rechecked and it is the well-known nearest-neighbor antiferromagnetic ground state, which can be attributed to the hole-mediated superexchange through the strong pdσ hybridization interaction between Cu dx2-y2 electron and the neighboring oxygen px (or py) electron. Under each present experimental condition, the Sm vacancy has a very high formation energy and is unlikely to be stable. The Cu vacancy is a shallow acceptor, which is preferred under O-rich conditions, whereas the O vacancy is a donor and energetically favorable under O-poor conditions. To construct its (001) surface structure, CuOO, CuO, and Cu terminated surfaces are found to be most favorable under different experimental conditions. The stable surface structures are always accompanied by significant surface atomic reconstructions and electron charge redistribution, which are intimately correlated to each other.

Advanced technologies related to a high temperature superconductor for small laboratory experiments

International Nuclear Information System (INIS)

Ogawa, Yuichi; Mito, Toshiyuki; Yanagi, Nagato

2006-01-01

Advanced technologies related to a high temperature superconductor materials and small refrigerator are reviewed. Mini-RT/RT-1 is designed and constructed as a plasma examination device. The element technology of low temperature apparatus, the results of performance tests and application examples are explained. The superconductors such as Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) for the low temperature phase, Bi 2 Sr 2 Ca 2 Cu 3 O 10 (Bi-2223) for the high temperature phase, and YBa 2 Cu 3 O y (YBCO or Y123) are described. Advanced 4K-Giford-Mcmahon (GM) refrigerator on the market put superconductor coil made of low temperature superconductor metals to practical use and extends its application field. Small laboratory is able to experiment on the high temperature superconductor materials. (S.Y.)

Microscopic theory of ultrasonic attenuation in high-Tc superconductors in normal state

International Nuclear Information System (INIS)

Bishoyi, K.C.; Rout, G.C.; Behera, S.N.

2001-01-01

The mechanism of the ultrasonic attenuation in high temperature superconductors is not yet studied thoroughly both experimentally and theoretically. A microscopic theoretical model is proposed here to study the attenuation in the electron doped and hole doped compounds like L 2-x M x CuO 4 (L=La,Nd; M=Sr,Ca,Ce). The model Hamiltonian contains the staggered magnetic field in the d-electrons of copper, the doped f-electrons term and the hybridisation between d- and f-electrons. The electron-phonon interaction arises due to the volume strain dependence of the hybridisation. The phonon Green's function is calculated by equations of motion of Zubarev technique. The temperature dependence of the ultrasonic attenuation coefficient (α) is calculated from the imaginary part of the phonon self energy and the velocity of sound in the dynamic and long wavelength limit. The dimensionless parameters involved in the calculations are the electron-phonon coupling (g), staggered magnetic field (h) , hybridization (υ), position of the f-level (d), frequency (ω), and temperature (t). The results are discussed. (author)

Superconductivity drives magnetism in δ -doped La2CuO4

Science.gov (United States)

Suter, A.; Logvenov, G.; Boris, A. V.; Baiutti, F.; Wrobel, F.; Howald, L.; Stilp, E.; Salman, Z.; Prokscha, T.; Keimer, B.

2018-04-01

Understanding the interplay between different orders in a solid is a key challenge in highly correlated electronic systems. In real systems this is even more difficult since disorder can have strong influence on the subtle balance between these orders and thus can obscure the interpretation of the observed physical properties. Here we present a study on δ -doped La2CuO4 (δ -LCON ) superlattices. By means of molecular beam epitaxy whole LaO2 layers were periodically replaced by SrO2 layers, providing a charge reservoir yet reducing the level of disorder typically present in doped cuprates to an absolute minimum. The induced superconductivity and its interplay with the antiferromagnetic order is studied by means of low-energy muon spin rotation. We find a quasi-two-dimensional superconducting state which couples to the antiferromagnetic order in a nontrivial way. Below the superconducting transition temperature, the magnetic volume fraction increases strongly. The reason could be a charge redistribution of the free carriers due to the opening of the superconducting gap which is possible due to the close proximity and low disorder between the different ordered regions.

Synthesis of a new compound - Sr2CuO2CO3

International Nuclear Information System (INIS)

Fomichev, D.V.; Khardanov, A.L.; Antipov, E.V.; Kovba, L.M.

1990-01-01

A new compound of Sr 2 CuO 2 CO 3 composition, being an intermediate product of solid phase synthesis in air in SrCo 3 -CuO system at T 2 CuO 2 CO 3 have low resistance at room temperature and semiconductor type conductivity

High resolution T{sub 2}{sup *}-weighted magnetic resonance imaging at 3 Tesla using PROPELLER-EPI

Energy Technology Data Exchange (ETDEWEB)

Kraemer, Martin; Reichenbach, Juergen R. [Jena University Hospital (Germany). Medical Physics Group

2014-09-01

We report the application of PROPELLER-EPI for high resolution T{sub 2}{sup *}-weighted imaging with sub-millimeter in-plane resolution on a clinical 3 Tesla scanner. Periodically rotated blades of a long-axis PROPELLER-EPI sequence were acquired with fast gradient echo readout and acquisition matrix of 320 x 50 per blade. Images were reconstructed by using 2D-gridding, phase and geometric distortion correction and compensation of resonance frequency drifts that occurred during extended measurements. To characterize these resonance frequency offsets, short FID calibration measurements were added to the PROPELLER-EPI sequence. Functional PROPELLER-EPI was performed with volunteers using a simple block design of right handed finger tapping. Results indicate that PROPELLER-EPI can be employed for fast, high resolution T{sub 2}{sup *}-weighted imaging provided geometric distortions and possible resonance frequency drifts are properly corrected. Even small resonance frequency drifts below 10 Hz as well as non-corrected geometric distortions degraded image quality substantially. In the initial fMRI experiment image quality and signal-to-noise ratio was sufficient for obtaining high resolution functional activation maps. (orig.)

Anisotropy of superconducting transformation in magnetic fields in Nd sub 1 sub . sub 8 sub 5 Ce sub 0 sub . sub 1 sub 5 CuO sub 4 monocrystal

CERN Document Server

Panova, G K; Chernoplekov, N A; Emelchenko, G A; Malyuk, A N; Lin, S T

2002-01-01

The anisotropy of the superconducting properties of the Nd sub 1 sub . sub 8 sub 5 Ce sub 0 sub . sub 1 sub 5 CuO sub 4 monocrystal is studied by resistance within the temperature range of 2-30 K in the 0, 1, 2, 4, 6 Tl magnetic fields in the a-b plane. The T sub c (H) and H sub c sub 2 (T) strong anisotropy was observed by the magnetic field different orientation in the a-b plane. The zero direction in the gap of the order parameter is determined. The analysis of the experimental data shows, that such a result may be related to the change in the symmetry in the copper atoms surrounding, leading to its reduction from the tetragonal to orthorhombic one in the low-temperature area. The comparison with the La sub 1 sub . sub 8 sub 5 Sr sub 0 sub . sub 1 sub 5 CuO sub 4 gives all grounds to suppose, that the superconductivity mechanism in the electron- and hole-doped superconductor is similar and the observed difference is connected with the structure peculiarities

Thermal properties of GdSr{sub 2}RuCu{sub 2}O{sub 8-{delta}} based mixtures in the GdSr{sub 2}RuO{sub 6}-CuO pseudo-binary system

Energy Technology Data Exchange (ETDEWEB)

Gombos, Marcello [Laboratorio Regionale Supermat CNR-INFM Via Salvador Allende, I-84081 Baronissi (Italy); Dipartimento di Fisica ' E.R.Caianiello' , Universita di Salerno, Via Salvador Allende, I-84081 Baronissi (Italy)], E-mail: gombos@sa.infn.it; Ciancio, Regina; Vecchione, Antonio; Pace, Sandro [Laboratorio Regionale Supermat CNR-INFM Via Salvador Allende, I-84081 Baronissi (Italy); Dipartimento di Fisica ' E.R.Caianiello' , Universita di Salerno, Via Salvador Allende, I-84081 Baronissi (Italy)

2007-09-01

GdSr{sub 2}RuCu{sub 2}O{sub 8-{delta}} (Gd1212) rutheno-cuprate compound is widely studied because it shows the coexistence of superconductivity and highly anisotropic magnetic ordering in the same cell. Anyway the nature of the magnetic ordering is still debated and the fabrication of macroscopic samples oriented along a crystallographic axis, that could help to clarify its details, appears to be quite difficult. For this reason, accurate investigation on Gd1212 incongruent melting reaction, producing liquid copper oxide and the solid GdSr{sub 2}RuO{sub 6} (Gd1210), appears to be necessary to improve the fabrication of crystallographically oriented bulk superconducting samples. Thermo-gravimetric and differential thermal measurements were performed to analyse the thermal behaviour up to 1200 deg. C and the melting temperatures of different mixtures of Gd1212 with Gd1210 or CuO, in view to perform a scan of the whole CuO-Gd1212-Gd1210 coexistence line of the Gd-Sr-Ru-Cu-O phase diagram. Dependence on the atmosphere and the formation of different spurious phases was also studied.

A new series of oxycarbonate superconductors (Cu{sub 0.5}C{sub 0.5}){sub m}Ba{sub m+1}Ca{sub n-1}Cu{sub n}O{sub 2}({sub m+n})+1

Energy Technology Data Exchange (ETDEWEB)

Takayama-Muromachi, E.; Kawashima, T.; Matsui, Y. [National Institute for Research in Inorganic Materials, Ibaraki (Japan)

1994-12-31

We found a new series of oxycarbonate superconductors in the Ba-Ca-Cu-C-O system under high pressure of 5 GPa. Their ideal formula is (Cu{sub 0.5}C{sub 0.5}){sub m}Ba{sub m+1}Ca{sub n-1}Cu{sub n}O{sub 2}({sub m+n})+1 ((Cu,C)-m(m+1)(n-1)n). Thus far, n=3, 4 members of the m=1 series, (Cu,C)-1223 and (Cu,C)-1234, have been prepared in bulk while n=4, 5 members, (Cu,C)-2334 and (Cu,C)-2345, have been prepared for the m=2 series. (Cu,C)-1223 shows superconductivity below 67 K while T{sub c}`s of other compounds are above 110 K. In particular, (Cu,C)=1234 has the highest T{sub c} of 117 K.

Effect of BSO addition on Cu-O bond of GdBa{sub 2}Cu{sub 3}O{sub 7-x} films with varying thickness probed by extended x-ray absorption fine structure

Energy Technology Data Exchange (ETDEWEB)

Jeon, H. K.; Lee, J. K.; Yang, D. S.; Kang, B. [Chungbuk National University, Cheongju (Korea, Republic of); Kang, W. N. [Dept. of Physics, Sungkyunkwan University, Suwon (Korea, Republic of)

2016-12-15

We investigated the relation between the Cu-O bond length and the superconducting properties of BaSnO{sub 3} (BSO)-added GdBa{sub 2}Cu{sub 3}O{sub 7-x} (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% BaSnO{sub 3} (BSO) added GdBa{sub 2}Cu{sub 3}O{sub 7-x} (GdBCO) thin films with varying thickness from 0.2 μm to 1.0 μm were fabricated by using pulsed laser deposition (PLD) method. The transition temperature (T{sub c}) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to 0.8 μm, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of T{sub c} and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

Phase transitions to dipolar clusters and charge density waves in high T{sub c} superconductors

Energy Technology Data Exchange (ETDEWEB)

Saarela, M., E-mail: Mikko.Saarela@oulu.fi [Department of Physics, University of Oulu, P.O. Box 3000, FIN-90014 (Finland); Kusmartsev, F.V. [Department of Physics, Loughborough University, LE11 3TU (United Kingdom)

2017-02-15

We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.

Energetics and crystal chemistry of Ruddlesden-Popper type structures in high T(sub c) ceramic superconductors

Science.gov (United States)

Dwivedi, Anurag; Cormack, A. N.

1990-01-01

The formation of Ruddlesden-Popper type layers (alternating slabs of rocksalt and perovskite structures) is seen in these oxides which is similar in many respects to what is seen in the system Sr-Ti-O. However, it was observed that there are some significant differences, for example the rocksalt and perovskite blocks in new superconducting compounds are not necessarily electrically, unlike in Sr-Ti-O systems. This will certainly render an additional coulombic bonding energy between two different types of blocks and may well lead to significant differences in their structural chemistry. In the higher order members of the various homologous series, additional Cu-O planes are inserted in the perovskite blocks. In order for the unit cell to electrically neutral the net positive charge on rocksalt block (which remains constant throughout the homologous series) should be balanced by an equal negative charge on perovskite block. It, thus becomes necessary to create oxygen vacancies in the basic perovskite structure, when width of the perovskite slab changes on addition of extra Cu-O planes. Results of atomistic simulations suggest that these missing oxygen ions allow the Cu-O planes to buckle in these compounds. This is also supported by the absence of buckling in the first member of Bi-containing compounds in which there are no missing oxygen ions and the Sr-Ti-O series of compounds. Additional results are presented on the phase stability of polytypoid structures in these crystal chemically complex systems. The studies will focus on the determination of the location of Cu(3+) in the structures of higher order members of the La-Cu-O system and whether Cu(3+) ions or oxygen vacancies are energetically more favorable charge compensating mechanism.

Conventional proximity effect in bilayers of superconducting underdoped $La_{1.88}Sr_{0.12}CuO_4$ islands coated with non superconducting overdoped $La_{1.65}Sr_{0.35}CuO_4$

OpenAIRE

Koren, G.; Millo, O.

2009-01-01

Following a recent study by our group in which a large $T_c$ enhancement was reported in bilayers of the non-superconducting $La_{1.65}Sr_{0.35}CuO_4$ and superconducting $La_{1.88}Sr_{0.12}CuO_4$ films [Phys. Rev. Lett. \\textbf{101}, 057005 (2008)], we checked if a similar effect occurs when superconducting $La_{1.88}Sr_{0.12}CuO_4$ islands are coated with a continuous layer of the non superconducting $La_{1.65}Sr_{0.35}CuO_4$. We found that no such phenomenon is observed. The bare supercond...

Critical behavior of order-parameter fluctuations in liquid 4He near T/sub lambda/

International Nuclear Information System (INIS)

Lambert, B.; Perzynski, R.; Salin, D.

1979-01-01

We hve measured the critical attenuation of first sound in liquid 4 He from 550 to 1700 MHz. We can describe the attenuation due to the fluctuations of the order parameter up to 1.7 GHz, using experimental data at lower frequencies from various authors. Above T/sub lambda/, the fluctuations are the only phenomena and are analyzed with a scaling function of ωtau 2 with a characteristic time tau 2 = 2 x 10 -12 x t/sup -1.062/ sec, t = vertical-bar (T-T/sub lambda/)/T/sub lambda/vertical-bar. Below T/sub lambda/, several phenomena are present. In the range of 1 GHz, the main contribution is due to the fluctuations. We demonstrate experimentally that the fluctuation attenuation is not symmetric about T/sub lambda/. We fit our data with a scaling function of ωtau 2

Superconductivity and spin gap in the zigzag-chain t-J model simulating a CuO double chain in Pr2Ba4Cu7O15-δ

International Nuclear Information System (INIS)

Sano, Kazuhiro; Ono, Yoshiaki

2007-01-01

Using the numerical diagonalization method, we examine the one-dimensional t 1 -t 2 -J 1 -J 2 model (zigzag-chain t-J model) which is an effective model for metallic CuO double chains in the super-conductor Pr 2 Ba 4 Cu 7 O 15-δ . Based on the Tomonaga-Luttinger liquid theory, we calculate the Luttinger liquid parameter K ρ as a function of the electron density n. It is found that superconductivity is realized in the parameter region, which is in accordance with experimental results. We show the phase diagram of a spin gap in the t 2 /|t 1 |-n plane by analyzing the expectation value of the twist operator Z σ in the spin sector. The spin gap appears in the region with a large t 2 /|t 1 |, where the phase boundary at half filling is consistent with that of the known frustrated quantum spin system. The analysis also suggests that the estimated value of the spin gap reaches ∼100 K in the realistic parameter region of Pr 2 Ba 4 Cu 7 O 15-δ . (author)

Specific heat jump at T/sub c/ of proximity effect sandwiches containing nonmagnetic localized states

International Nuclear Information System (INIS)

Maneeratankul, S.; Tang, I.M.

1987-01-01

The decrease in the transition temperature and the jump in the specific heat at T/sub c/ of proximity effect sandwiches containing nonmagnetic Anderson impurities in the normal layer are studied. The effects of the resonant scattering by the impurities are treated in the same manner as that used by Kaiser in his study of the effects of resonant scattering on the properties of bulk superconductors. Numerical calculations of the decrease in T/sub c/ and the jump in the specific heat at T/sub c/ as a function of the thickness of the normal layer are presented

Room temperature synthesis of 2D CuO nanoleaves in aqueous solution

International Nuclear Information System (INIS)

Zhao Yan; Li Yunling; Wang Zichen; Zhao Jingzhe; Ma Dechong; Hou Shengnan; Li Linzhi; Hao Xinli

2011-01-01

A simple room temperature method was reported for the synthesis of CuO nanocrystals in aqueous solution through the sequence of Cu 2+ → Cu(OA) 2 → Cu(OH) 2 → Cu(OH) 4 2- → CuO. Sodium oleate (SOA) was used as the surfactant and shape controller. The as-prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy (UV-vis) and differential thermal analysis (DTA). It can be seen that 1D Cu(OH) 2 nanowires were first obtained from Cu(OA) 2 and, at room temperature, converted into 2D CuO nanoleaves (CuO NLs) in a short time under a weakly basic environment. On prolonging the reaction time, the top part of these 2D nanoleaves branched and separated along the long axis to form 1D rod-like nano-CuO because of the assistance of SOA. A possible transformation mechanism of Cu(OH) 2 to CuO nanostructures at room temperature in aqueous solution is discussed. The transformation velocity can be controlled by changing the pH value of the system. The prepared CuO NLs were used to construct an enzyme-free glucose sensor. The detecting results showed that the designed sensor exhibited good amperometric responses towards glucose with good anti-interferent ability.

Probing the singlet character of the two-hole states in cuprate superconductors

NARCIS (Netherlands)

Ghiringhelli, G; Brookes, NB; Tjeng, LH; Mizokawa, T; Tjernberg, O; Menovsky, AA; Steeneken, P.G.

Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the

Effects of the Seed Distance on the Characteristics of the (100)/(100) Junctions of Top-Seeded Melt Growth Processed YBCO Superconductors Using Two Seeds

Energy Technology Data Exchange (ETDEWEB)

Kim, C.J.; Gee, Y.A.; Hong, G.Y. [Korea Atomic Energy Research Institute, Taejon (Korea); Kim, H.J.; Joo, J.H. [Sungkyunkwan University, Suwon (Korea); Han, S.C.; Han, Y.H.; Sung, T.H.; Kim, S.J. [Korea Electric Power Research Institute, Taejon (Korea)

1999-06-01

The effects of the distance (d) between two Sm{sub 1.8}Ba{sub 2.4}Cu{sub 3.4}Ox seeds on the characteristics of the (100)/(100) junctions of top-seeded melt growth processed YBCO superconductors were investigated. The trapped magnetic field at the grain junction and the levitation force of the top surface decreased with increasing d value. The degradation of the properties is attributed to the presence of the residual melt-forming phases (CuO and BaCUO{sub 2}) at the grain junction, whose amount depends on the d value. (author). 18 refs., 10 figs.

Effects of radiation damage in ion-implanted thin films of metal-oxide superconductors

International Nuclear Information System (INIS)

Clark, G.J.; Marwick, A.D.; Koch, R.H.; Laibowitz, R.B.

1987-01-01

The effects of ion implantation into thin films of the superconductor YBa 2 Cu 3 O/sub x/ have been studied. Using oxygen and arsenic ions, the superconducting transition temperature T/sub c/, the change in room-temperature electrical properties from conducting to insulating, and the crystalline to amorphous structural transition in the films were studied as a function of ion dose. The deposited energy required to change T/sub c/ was found to be 0.2 eV/atom, while 1--2 eV/atom was required to affect the room-temperature conductivity, and 4 eV/atom to render the film amorphous. This hierarchy of effects is discussed in terms of the damage mechanisms involved

The oxygen isotope effect on the in-plane penetration depth in cuprate superconductors

Energy Technology Data Exchange (ETDEWEB)

Khasanov, R [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Shengelaya, A [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Morenzoni, E [Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Conder, K [Laboratory for Neutron Scattering, ETH Zuerich and PSI Villigen, CH-5232 Villigen PSI (Switzerland); Savic, I M [Faculty of Physics, University of Belgrade, 11001 Belgrade (Serbia and Montenegro); Keller, H [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland)

2004-10-13

Muon spin rotation ({mu}SR) studies of the oxygen isotope ({sup 16}O/{sup 18}O) effect (OIE) on the in-plane magnetic field penetration depth {lambda}{sub ab} in cuprate high-temperature superconductors (HTS) are presented. First, the doping dependence of the OIE on the transition temperature T{sub c} in various HTS is briefly discussed. It is observed that different cuprate families show similar doping dependences of the OIE on T{sub c}. Then, bulk {mu}SR, low-energy {mu}SR, and magnetization studies of the total and site-selective OIE on {lambda}{sub ab} are described in some detail. A substantial OIE on {lambda}{sub ab} was observed in various cuprate families at all doping levels, suggesting that cuprate HTS are non-adiabatic superconductors. The experiments clearly demonstrate that the total OIE on T{sub c} and {lambda}{sub ab} arise from the oxygen sites within the superconducting CuO{sub 2} planes, demonstrating that the phonon modes involving the movement of planar oxygen are dominantly coupled to the supercarriers. Finally, it is shown that the OIE on T{sub c} and {lambda}{sub ab} exhibit a relation that appears to be generic for different families of cuprate HTS. The observation of these unusual isotope effects implies that lattice effects play an essential role in cuprate HTS and have to be considered in any realistic model of high-temperature superconductivity.

Structural properties of as-grown and reduced Pr2CuO4 single crystals investigated by ion channeling

International Nuclear Information System (INIS)

Haga, T.; Abe, Y.

1996-01-01

Ion channeling is very sensitive to atomic arrangements and small atomic displacements in real space. Thus, in order to clarify a role of reduction for Pr 2 CuO 4 , ion channeling properties for the materials have been measured in detail. Anomalous increases of dechanneling fractions of Cu and O atoms in the reduced samples have been found. These results could not be explained by the apical oxygen model but probably suggest that O atoms in Cu-O planes are removed by reduction. Taking these results into account, correlation between lattice instability and superconductivity in the material will be discussed. (orig.)

Heterometallic and homometallic complexes containing bifunctional ligands and their application in high-temperature oxide superconductor materials

Science.gov (United States)

Breeze, Steven R.

We have been interested in the development of soluble precursors for the production of YBasb2Cusb3Osb{7-delta} and Bisb2(Ca,Sr)sbn+1CusbnOsb(2n + 4) + delta, superconductor materials. Several heterometallic and homometallic complexes containing the constituent metals of these superconductors and bifunctional ligands such as aminoalcohols, acetates and thioethers have been isolated and structurally characterized. The thermal decomposition properties and magnetic properties of some of these compounds have been investigated. The first ligand system investigated involved 1,3-bis(dimethylamino)-2-propanol (bdmapH). By varying the ratio of bdmapH, Cu(OCHsb3)sb2, and M(Osb2CCFsb3)sb2 (M = Ca, Sr) several heterometallic complexes have been obtained, including Srsb2Cusb2(bdmap)sb4(Osb2CCFsb3)sb4, CaCu(bdmap)sb2(Osb2CCFsb3)sb3(Hsb2O), Srsb2Cusb4(bdmap)sb6-(Osb2CCFsb3)sb4(musb 3-OH)sb2(THF)sb2 and SrCusb2(bdmap)sb3(Osb2CCFsb3)sb3(THF). With the exception of Srsb2Cusb4(bdmap)sb6(Osb2CCFsb3)sb4(musb 3-OH)sb2(THF)sb2, these compounds thermally decompose to form mixtures of fluorides and oxides. An analogous acetate compound SrCusb2(bdmap)sb3(Osb2CCHsb3)sb3(THF) has been produced, which forms the corresponding oxide at high temperature. A bismuth dimer, Bisb2(bdmap)sb2(Osb2CCHsb3)sb4(Hsb2O), has also been obtained. Superconducting powder of the Bisb2Srsb2CaCusb2Osb{8 + delta} and epitaxial superconducting films of the YBasb2Cusb3Osb{7-delta} superconductor have been produced using the bdmap and acetate ligands as cross-linking reagents. The second ligand system investigated involved di-2-pyridylmethanediol. Only homonuclear complexes have been obtained by using this ligand, including the mononuclear compound Cu ((2-py)sb2CO(OH)) sb2(HOsb2CCH sb3)sb2*CHsb2Clsb2, the tetranuclear compound Cusb4 ((2-py)sb2CO(OH)) sb2(Osb2CCHsb 3)sb6(Hsb2O)sb2*CHsb2Clsb2, and the bismuth dimer Bisb2 ((2-py)sb2CO(OH)) sb2(Osb 2CCFsb3)sb4*(THF)sb2. The tetranuclear Cusb4 compound was found to be

Evidence of a spin resonance mode in the iron-based superconductor Ba(0.6)K(0.4)Fe2As2 from scanning tunneling spectroscopy.

Science.gov (United States)

Shan, Lei; Gong, Jing; Wang, Yong-Lei; Shen, Bing; Hou, Xingyuan; Ren, Cong; Li, Chunhong; Yang, Huan; Wen, Hai-Hu; Li, Shiliang; Dai, Pengcheng

2012-06-01

We used high-resolution scanning tunneling spectroscopy to study the hole-doped iron pnictide superconductor Ba(0.6)K(0.4)Fe(2)As(2) (T(c)=38 K). Features of a bosonic excitation (mode) are observed in the measured quasiparticle density of states. The bosonic features are intimately associated with the superconducting order parameter and have a mode energy of ~14 meV, similar to the spin resonance measured by inelastic neutron scattering. These results indicate a strong electron-spin excitation coupling in iron pnictide superconductors, similar to that in high-T(c) copper oxide superconductors.

Designing 3D highly ordered nanoporous CuO electrodes for high-performance asymmetric supercapacitors.

Science.gov (United States)

Moosavifard, Seyyed E; El-Kady, Maher F; Rahmanifar, Mohammad S; Kaner, Richard B; Mousavi, Mir F

2015-03-04

The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. Herein, we report a simple, yet effective, strategy for high-performance supercapacitors by building three-dimensional pseudocapacitive CuO frameworks with highly ordered and interconnected bimodal nanopores, nanosized walls (∼4 nm) and large specific surface area of 149 m(2) g(-1). This interesting electrode structure plays a key role in providing facilitated ion transport, short ion and electron diffusion pathways and more active sites for electrochemical reactions. This electrode demonstrates excellent electrochemical performance with a specific capacitance of 431 F g(-1) (1.51 F cm(-2)) at 3.5 mA cm(-2) and retains over 70% of this capacitance when operated at an ultrafast rate of 70 mA cm(-2). When this highly ordered CuO electrode is assembled in an asymmetric cell with an activated carbon electrode, the as-fabricated device demonstrates remarkable performance with an energy density of 19.7 W h kg(-1), power density of 7 kW kg(-1), and excellent cycle life. This work presents a new platform for high-performance asymmetric supercapacitors for the next generation of portable electronics and electric vehicles.

The superconductor (Tl,Hg,Ca)2(Ba,Sr)2(Ca,Sr,Tl)Cu2O7.6

International Nuclear Information System (INIS)

Valldor, M.; Bryntse, I.; Morawski, A.

2002-01-01

In the title 2212-type superconductor (thallium mercury calcium barium strontium copper oxide), which contains both Tl and Hg in the charge reservoir (CR), Sr is located at both alkali-earth (AE) metal sites. Ca enters the CR at the same time as Tl shares the smaller AE site, which increases the apical Cu-Cu distance significantly. The structure causes the superconducting Cu-O layers to become significantly puckered. (orig.)

A {mu}SR study of the magnetoresistive ruthenocuprates RuSr{sub 2}Nd{sub 1.8-x}Y {sub 0.2}Ce{sub x}Cu{sub 2}O{sub 10-{delta}} (x = 0.95 and 0.80)

Energy Technology Data Exchange (ETDEWEB)

Mclaughlin, A C [Department of Chemistry, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE (United Kingdom); Attfield, J P [Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King' s Buildings, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom); Van Duijn, J [Instituto de Investigacion en EnergIas Renovables, Universidad de Castilla la Mancha, Albacete, E02006 (Spain); Hillier, A D, E-mail: a.c.mclaughlin@abdn.ac.uk [ISIS facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX (United Kingdom)

2011-09-14

Zero field muon spin relaxation (ZF-{mu}SR) has been used to study the magnetic properties of the underdoped giant magnetoresistive ruthenocuprates RuSr{sub 2}Nd{sub 1.8-x}Y {sub 0.2}Ce{sub x}Cu{sub 2}O{sub 10-{delta}} (x = 0.95, 0.80). The magnetoresistance (MR) is defined so that MR = (({rho}{sub H}-{rho}{sub 0})/{rho}{sub 0}) and the giant magnetoresistive ruthenocuprates RuSr{sub 2}Nd{sub 1.8-x}Y {sub 0.2}Ce{sub x}Cu{sub 2}O{sub 10-{delta}} exhibit a large reduction in electronic resistivity upon application of a magnetic field. The ZF-{mu}SR results show a gradual loss of initial asymmetry A{sub 0} at the ruthenium spin transition temperature, T{sub Ru}. At the same time the electronic relaxation rate, {lambda}, shows a gradual increase with decreasing temperature below T{sub Ru}. These results have been interpreted as evidence for Cu spin cluster formation below T{sub Ru}. These magnetically ordered clusters grow as the temperature is decreased thus causing the initial asymmetry to decrease slowly. Giant magnetoresistance is observed over a wide temperature range in the materials studied and the magnitude increases as the temperature is reduced from T{sub Ru} to 4 K which suggests a relation between Cu spin cluster size and |-MR|. (paper)

Study of Optical Band Gap of CuO Using Fermi's Golden Rule

International Nuclear Information System (INIS)

Nemade, K R; Waghuley, S A

2012-01-01

Quantum size effect where the electronic and optical properties of solids are altered due to changes in the band structures, enhanced the surface/volume ratio in nano dimensions forces more than 33% of the atoms to be on the surface (for 10nm dot 35), which drastically altering the physical properties such as having lower melting temperature and lower sintering temperature, and higher diffusion force at elevated temperatures. Consequently, its Fermi's golden rule analysis becomes crucial. Cupric oxide (CuO) is an important transition metal oxide with the basis of several high temperature superconductors and giant magnetoresistance materials. In present investigation, optical Band Gap from UV data using Fermi's golden rule for single step chemically synthesized CuO was computed.

A new way for preparing superconducting materials: the electrochemical oxidation of La2CuO4

International Nuclear Information System (INIS)

Wattiaux, A.; Park, J.C.; Grenier, J.C.; Pouchard, M.

1990-01-01

The electrochemical oxidation in alkaline medium is described as a new way for preparing superconducting oxides at room temperature. The application of this method to La 2 CuO 4 gave rise to a metallic material with a superconducting behaviour below 39 K and whose physical and chemical features appear as quite promising [fr

(D-Pen2,4 prime -125I-Phe4,D-Pen5)enkephalin: A selective high affinity radioligand for delta opioid receptors with exceptional specific activity

Energy Technology Data Exchange (ETDEWEB)

Knapp, R.J.; Sharma, S.D.; Toth, G.; Duong, M.T.; Fang, L.; Bogert, C.L.; Weber, S.J.; Hunt, M.; Davis, T.P.; Wamsley, J.K. (Department of Pharmacology, University of Arizona, College of Medicine, Tucson (United States))

1991-09-01

(D-Pen2,4{prime}-125I-Phe4,D-Pen5)enkephalin ((125I)DPDPE) is a highly selective radioligand for the delta opioid receptor with a specific activity (2200 Ci/mmol) that is over 50-fold greater than that of tritium-labeled DPDPE analogs. (125I)DPDPE binds to a single site in rat brain membranes with an equilibrium dissociation constant (Kd) value of 421 {plus minus} 67 pM and a receptor density (Bmax) value of 36.4 {plus minus} 2.7 fmol/mg protein. The high affinity of this site for delta opioid receptor ligands and its low affinity for mu or kappa receptor-selective ligands are consistent with its being a delta opioid receptor. The distribution of these sites in rat brain, observed by receptor autoradiography, is also consistent with that of delta opioid receptors. Association and dissociation binding kinetics of 1.0 nM (125I) DPDPE are monophasic at 25 degrees C. The association rate (k + 1 = 5.80 {plus minus} 0.88 {times} 10(7) M-1 min-1) is about 20- and 7-fold greater than that measured for 1.0 nM (3H) DPDPE and 0.8 nM (3H) (D-Pen2,4{prime}-Cl-Phe4, D-Pen5)enkephalin, respectively. The dissociation rate of (125I)DPDPE (0.917 {plus minus} 0.117 {times} 10(-2) min-1) measured at 1.0 nM is about 3-fold faster than is observed for either of the other DPDPE analogs. The rapid binding kinetics of (125I)DPDPE is advantageous because binding equilibrium is achieved with much shorter incubation times than are required for other cyclic enkephalin analogs. This, in addition to its much higher specific activity, makes (125I)DPDPE a valuable new radioligand for studies of delta opioid receptors.

Effects of disorder on the intrinsically hole-doped iron-based superconductor KC a2F e4A s4F2 by cobalt substitution

Science.gov (United States)

Ishida, Junichi; Iimura, Soshi; Hosono, Hideo

2017-11-01

In this paper, the effects of cobalt substitution on the transport and electronic properties of the recently discovered iron-based superconductor KC a2F e4A s4F2 , with Tc=33 K , are reported. This material is an unusual superconductor showing intrinsic hole conduction (0.25 holes /F e2 + ). Upon doping of Co, the Tc of KC a2(Fe1-xC ox) 4A s4F2 gradually decreased, and bulk superconductivity disappeared when x ≥0.25 . Conversion of the primary carrier from p type to n type upon Co-doping was clearly confirmed by Hall measurements, and our results are consistent with the change in the calculated Fermi surface. Nevertheless, neither spin density wave (SDW) nor an orthorhombic phase, which are commonly observed for nondoped iron-based superconductors, was observed in the nondoped or electron-doped samples. The electron count in the 3 d orbitals and structural parameters were compared with those of other iron-based superconductors to show that the physical properties can be primarily ascribed to the effects of disorder.

Powder processing of high Tc oxide superconductors and their properties

International Nuclear Information System (INIS)

Vajpei, A.C.; Upadhyaya, G.S.

1992-01-01

Powder processing of ceramics is an established technology and in the area of high T c superconductors, its importance is felt even more significantly. The present monograph is an attempt in this direction to explore the perspectives and practice of powder processing routes towards control and optimization of the microstructure and pertinent properties of high T c oxide superconductors. The monograph consists of 6 chapters. After a very brief introduction (Chapter 1), Chapter 2 describes various classes of high T c oxide superconductors and their phase equilibria. Chapter 3 highlights the preparation of oxide superconductor powders through various routes and details their subtle distinctions. Chapter 4 briefly covers characterisation of the oxide superconductors, laying emphasis on the process-analysis and microstructure. Chapter 5 describes in detail various fabrication techniques for bulk superconductors through the powder routes. The last Chapter (Chapter 6) describing properties of bulk oxide superconductors, discusses the role of subtituents, compositional variations and processing methods on such properties. References are given at the end of each chapter. (orig.)

Investigations into the electronic structure of the high-Tc superconductors by means of photoelectron spectroscopy

International Nuclear Information System (INIS)

Dauth, B.H.

1989-08-01

The electronic structure of various polycrystalline samples including the new YBaCuO- and BiCaSrCuO- high T c superconductors (HTSC) and related systems is investigated by photoelectron spectroscopy. Additional characterization is performed by conductivity measurements. In particular, the binding energy of the Cu-2p 3/2 - and the O-1s-levels of various HTSC is determined. For the first time the controversial 531 eV oxygen line was shown to be an intrinsic electronic structure effect. Sintered CuO-samples are obtained for the first time. The electronic structure of the sintered CuO turns out to be drastically different with respect to pressed CuO powder. For the first time a crossover resonance from a O-1s- into a Cu-3d-level was observed with synchrotron radiation. This is additional evidence for the strong hybridization between the Cu-3d and the O-2p states. Photoemission spectroscopy shows that the holes in the HTSC's are located at the oxygen p-band. Fe and Al overlayers on the HTSC-samples induce a drastic change in the electronic properties of the interface: apparently oxygen is removed from the HTSC to the overlayer. (orig./BHO)

Neutron spectroscopic investigations on crystalline-electric-field and exchange interactions on high-Tc superconductors

International Nuclear Information System (INIS)

Staub, U.

1993-05-01

It is well known that in the high temperature superconductors of the type RBa 2 Cu 3 O x (123), with R=Y and most of the rare earths, superconductivity is believed to be controlled by the density of mobile charges in the copper oxide (CuO 2 ) planes. In particular, the charge transfer process from the chains to the planes seems to play an important role. In the 123, RBa 2 Cu 4 O 8 (1248) and the Bi 2 Sr 2 Ca 1-x Ho x Cu 2 O 8+δ (Bi2212) systems, the R ions are sandwiched between the CuO 2 planes, thus the crystalline electric field (CEF) interaction at the R sites constitutes an ideal probe of the local symmetry and the charge distribution of the superconducting planes. The (2J+1)-fold degeneracy of the ground-state J-multiplet of the rare earth ions will be partially lifted under the action of the CEF potential. By means of inelastic neutron scattering experiments it is possible to observe directly the transitions between the CEF states. Therefrom we obtain useful information on both the structure and the charge distribution in the vicinity of the R ion. In order to quantify the charge transfer process from the chains to the planes, we performed a detailed analysis of the CEF of Ho 3+ in the 123, 1248 and Bi2212 systems. In addition, we present some experiments on a Cl doped 123 sample and some external pressure experiments on the 123 system. In nearly all high-T c compounds RBa 2 Cu 3 O 7-δ superconductivity and magnetic ordering of the R ion sublattice coexist at low temperatures. In order to understand the interplay of magnetism and superconductivity in these systems, information on both the electronic ground state of the R 3+ ions and the coupling mechanisms between the R 3+ ions is highly desirable. (author) figs., tabs., 73 refs

Energy and polarization dependence of resonant inelastic X-ray scattering in Nd2CuO4

International Nuclear Information System (INIS)

Hill, J.P.; Kao, C.C.; Haemaelaeinen, K.

1998-01-01

The authors report the energy and polarization dependence of resonant inelastic x-ray scattering from Nd 2 CuO 4 . An energy loss feature at ∼6 eV is observed in the vicinity of the Cu K-edge. Numerical calculations based on the Anderson impurity model identify this as a charge transfer excitation to the anti-bonding state. The incident polarization is shown to select the intermediate states participating in the resonance process. Resonances are observed at 8,990 eV and 9,000 eV with the incident polarization perpendicular and parallel to the CuO planes, respectively. In contrast to the single-site model calculations, no resonances are observed associated with the 1s3d 10 L intermediate states, suggesting non-local effects play a role

Two classes of superconductors discovered in our material research: Iron-based high temperature superconductor and electride superconductor

International Nuclear Information System (INIS)

Hosono, Hideo

2009-01-01

We discovered two new classes of superconductors in the course of material exploration for electronic-active oxides. One is 12CaO . 7Al 2 O 3 crystal in which electrons accomodate in the crystallographic sub-nanometer-sized cavities. This material exhibiting metal-superconductor transition at 0.2 K is the first electride superconductor. The other is iron oxypnicitides with a layered structure. This superconductor is rather different from high T c cuprates in several respects. The high T c is emerged by doping carriers to the metallic parent phases which undergo crystallographic transition (tetra to ortho) and Pauli para to antiferromagnetic transition at ∼150 K. The T c is robust to impurity doping to the Fe sites or is induced by partial substitution of the Fe 2+ sites with Co 2+ or Ni 2+ . This article gives a brief summary of these discoveries and recent advances.

Magnetism and superconductivity of some Tl-Cu oxides

Science.gov (United States)

Datta, Timir

1991-01-01

Many copper oxide based Thallium compounds are now known. In comparison to the Bi-compounds, the Tl-system shows a richer diversity; i.e., High Temperature Superconductors (HTSC) can be obtained with either one or two Tl-0 layers (m = 1,2); also, the triple-digit phases are easier to synthesize. The value of d, oxygen stoichiometry, is critical to achieving superconductivity. The Tl system is robust to oxygen loss; Tl may be lost or incorporated by diffusion. A diffusion coefficient equal to 10 ms at 900 C was determined. Both ortho-rhombic and tetragonal structures are found, but HTSC behavior is indifferent to the crystal symmetry. This system has the highest T(sub c) confirmed. T(sub c) generally increases with p, the number of CuO layers, but tends to saturate at p = 3. Zero resistance was observed at temperatures as great as 125 K. Most of these HTSC's are hole type, but the Ce-doped specimens may be electronic. The magnetic aspects were studied; because in addition to defining the perfectly diamagnetic ground state as in conventional superconductors, magnetism of the copper oxides show a surprising variety. This is true of both the normal and the superconducting states. Also, due to the large phonon contribution to the specific heat at the high T(sub c) jump, electronic density of states, D(Ef), and coherence length are uncertain, and thus, are estimated from the magnetic results. Results from the Tl-system CuO, LaBaCuO,120 and the Bi-CuO compounds are discussed. The emphasis is on the role of magnetism in the Tl-CuO HTSC, but technological aspects are also pointed out.

Disappearance of superconductivity in the solid solution between (Ca4Al2O6)(Fe2As2) and (Ca4Al2O6)(Fe2P2) superconductors.

Science.gov (United States)

Shirage, Parasharam M; Kihou, Kunihiro; Lee, Chul-Ho; Takeshita, Nao; Eisaki, Hiroshi; Iyo, Akira

2012-09-19

The effect of alloying the two perovskite-type iron-based superconductors (Ca(4)Al(2)O(6))(Fe(2)As(2)) and (Ca(4)Al(2)O(6))(Fe(2)P(2)) was examined. While the two stoichiometric compounds possess relatively high T(c)'s of 28 and 17 K, respectively, their solid solutions of the form (Ca(4)Al(2)O(6))(Fe(2)(As(1-x)P(x))(2)) do not show superconductivity over a wide range from x = 0.50 to 0.95. The resultant phase diagram is thus completely different from those of other typical iron-based superconductors such as BaFe(2)(As,P)(2) and LaFe(As,P)O, in which superconductivity shows up when P is substituted for As in the non-superconducting "parent" compounds. Notably, the solid solutions in the non-superconducting range exhibit resistivity anomalies at temperatures of 50-100 K. The behavior is reminiscent of the resistivity kink commonly observed in various non-superconducting parent compounds that signals the onset of antiferromagnetic/orthorhombic long-range order. The similarity suggests that the suppression of the superconductivity in the present case also has a magnetic and/or structural origin.

Structural relationships in high temperature superconductors

International Nuclear Information System (INIS)

Schuller, I.K.; Segre, C.U.; Hinks, D.G.; Jorgensen, J.D.; Soderholm, L.; Beno, M.; Zhang, K.

1987-09-01

The recent discovery of two types of metallic copper oxide compounds which are superconducting to above 90 0 K has renewed interest in the search for new high temperature superconducting materials. It is significant that both classes of compounds, La/sub 2-x/Sr/sub x/CuO/sub 4-y/ and YBa 2 Cu 3 O/sub 7-δ/ are intimately related to the extensively studied perovskite family. Both compounds contain highly oxidized, covalently bonded Cu-O sublattices, however, they differ in geometry. In this paper we discuss the relationship of these features to the superconducting properties. 30 refs., 6 figs

Evaluation of oxygenation time in SmBa2Cu3O7-δ superconductors ceramics in air and ozone atmospheres

International Nuclear Information System (INIS)

Viana, P.R.P; Cunha, A.G.

2010-01-01

High temperature superconductors (HTSC) represent a major milestone in science. During the preparation of superconductors, oxygenation plays a key role, because oxygenation determines the distribution of charge carriers in these plans through the superconducting Cu-O and hence superconductivity. This paper proposes the preparation of polycrystalline superconductors using the ceramic method, and the step of oxygenation made with ozone gas (O 3 ). Ozone exerts chemical pressure on the compound, which has oxygen vacancies in its structure after the step of synthesis. The work was performed by varying the time between oxygenation 20, 40, 80 and 160 hours, with samples going through a process of oxygenation at 350 deg C after the step of synthesis. This study evaluates the time effect as oxygen can improve the superconducting properties such as resistivity and magnetic susceptibility. (author)

Uncovering a new quasi-2D CuO2 plane between the YBa2Cu3O7 and CeO2 buffer layer of coated conductors

Science.gov (United States)

Li, Zhi-Xin; Cao, Jin-Jin; Gou, Xiao-Fan; Wang, Tian-Ge; Xue, Feng

2018-01-01

We report a discovery of the quasi-two-dimensional (quasi-2D) CuO2 plane between the superconductor YBa2Cu3O7 (YBCO) and CeO2 buffer layer (mostly used in the fabrication) of coated conductors through the atomistic computer simulations with the molecular dynamics (MD) and first-principle calculations. For an YBCO coated conductor with multilayer structures, the buffer layers deposited onto a substrate are mainly considered to transfer a strong biaxial texture from the substrate to the YBCO layer. To deeply understand the tuning mechanism of the texture transfer, exploring the complete atomic-level picture of the structure between the YBa2Cu3O7/CeO2 interfaces is firstly required. However, the related observation data have not been available due to some big challenges of experimental techniques. With the MD simulations, having tested the accuracy of the potential functions for the YBa2Cu3O7/CeO2 interface, we constructed a total of 54 possible atom stacking models of the interface and identified its most appropriate and stable structure according to the criterion of the interface adhesion energy and the coherent characterization. To further verify the stability of the identified structure, we performed the first-principle calculations to obtain the adhesion energy and developed the general knowledge of the interface structure. Finally, a coherent interface formed with a new built quasi-2D CuO2 plane that is structurally similar to the CuO2 plane inside bulk YBCO was determined.

Infrared Zeeman study of the Nd.sup.3+./sup.-Cu.sup.2+./sup. anisotropic exchange interaction in Nd.sub.2./sub.CuO.sub.4./sub..

Czech Academy of Sciences Publication Activity Database

Richard, P.; Jandl, S.; Poirier, M.; Furnier, P.; Nekvasil, Vladimír; Sadowski, M.L.

2005-01-01

Roč. 72, č. 1 (2005), 014506/1-014506/10 ISSN 1098-0121 R&D Projects: GA ČR(CZ) GA202/03/0552 Institutional research plan: CEZ:AV0Z1010914 Keywords : cuprate superconductors * Nd 2 CuO 4 * Zeeman and Stark splitting * anisotropic exchange interaction Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.185, year: 2005

Exploring nuclear magnetic resonance at the highest pressure. Closing the pseudogap under pressure in a high temperature superconductor

Energy Technology Data Exchange (ETDEWEB)

Meissner, Thomas

2013-05-13

In the present work, a novel probe design for high pressure NMR experiments in gem anvil cells (GAC) was used which places a small microcoil inside the high pressure volume as the detection coil. Based on tests carried out at ambient pressure and high pressure of 42 kbar it is demonstrated that this approach is indeed feasible and results in an increase of sensitivity by two orders of magnitude compared to previous GAC-NMR designs. The design was then successfully employed in the investigation of the electronic properties of metallic aluminum and the high temperature superconductor YBa{sub 2}Cu{sub 4}O{sub 8} at pressures of up to 101 kbar. Because of its improved sensitivity and the potential to achieve even higher pressures, the microcoil GAC-NMR setup should prove useful in the investigation of materials under high pressure conditions in the future. In the case of metallic aluminum, the effect of pressure on the electronic density of states at the Fermi level was probed via the Knight-shift K and the spin-lattice relaxation time T{sub 1} at room temperature up to a pressure of 101 kbar, extending the pressure range of previous NMR measurements by a factor of 14 [72]. Most notably, a decrease of K(p) by 11% is detected in the investigated pressure range that is inconsistent with a free electron behavior of the density of states. Numerical band structure calculations that are in excellent agreement with the experimental data suggest that the observed changes of K and T{sub 1} are due to a kink in the electronic states at a Lifshitz-transition at about 75 kbar which has not been observed previously. A further decrease of K by a factor of 2 is predicted to occur in the pressure range up to 300 kbar. In addition, an increase of the NMR linewidths of the metallic aluminum signal was observed above about 42 kbar that is inconsistent with a pure dipolar linewidth. Based on an analysis of the field dependence of this effect it was ascribed to a small additional