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- YBa2Cu3O7 (2)
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Articles 1 - 26 of 26
Full-Text Articles in Physical Sciences and Mathematics
Chemical Activity In Yba2cu3o7 − Δ Across The Normal To Superconducting Phase Transition, Juana Vivó Acrivos
Chemical Activity In Yba2cu3o7 − Δ Across The Normal To Superconducting Phase Transition, Juana Vivó Acrivos
Faculty Publications, Chemistry
The Gibbs free enthalpy, chemical activity across the transition temperature to superconductivity, Tc in YBa2Cu3O7 − δ is obtained from reciprocally enhanced X-Ray absorbance, XAS and diffraction, XRD data near the Ba L3,2 edges' energy Ea, and orientations in the X-ray beam for preferred Miller indexed [HKL] planes' scattering, that are enhanced near Tc. The standard enthalpy and entropy for the formation of mixed normal metal/superconducting domains above Tc, determined individually across the two Ba L3,2 edges, to better than a percent accuracy: ΔH≠≥ = − 220 meV, and ΔS≠≥ = − 2 meV/K when 121 ≥ T ≥ 92 …
The Investigation Of Epr Paramagnetic Probe Line Width And Shape Temperature Dependence In High-Temperature Superconductors Of Bi–Pb–Sr–Ca–Cu–O System, J. G. Chigvinadze, Juana Vivó Acrivos, I. G. Akhvlediani, M. I. Chubabria, T. L. Kalabegishvili, T. I. Sanadze
The Investigation Of Epr Paramagnetic Probe Line Width And Shape Temperature Dependence In High-Temperature Superconductors Of Bi–Pb–Sr–Ca–Cu–O System, J. G. Chigvinadze, Juana Vivó Acrivos, I. G. Akhvlediani, M. I. Chubabria, T. L. Kalabegishvili, T. I. Sanadze
Faculty Publications, Chemistry
The work is related with the finding out of magnetic phases in strongly anisotropic high-temperature superconductor Bi1,7Pb0,3Sr2Ca2Cu3O10-δ in the temperature region where the superconductor is in the normal state. It was studied the temperature dependence of the paramagnetic probe EPR line width. In the normal state at T>Tc near 175 K it was revealed a pick in the temperature dependence of line width. In this region it was observed the time increase of the line width with the characteristic time ~ 17 min. This shows the possibility of magnetic phase formation in this material.
Yba2cu3o7 Electro-Magneto-Optic Effects In Ba L2,3 X-Ray Absorption Near Tc, Juana Vivó Acrivos
Yba2cu3o7 Electro-Magneto-Optic Effects In Ba L2,3 X-Ray Absorption Near Tc, Juana Vivó Acrivos
Faculty Publications, Chemistry
The onset of electro magneto-optic effects, observed at the Ba L2,3 edges synchrotron X-ray absorption by a YBa2Cu3O7 single crystal, 10 K above the transition temperature to superconductivity, Tc ~ 92 K is used to identify the role played by the Ba donor layer in the transition to superconductivity in the CuO2 layers. Negative permeability leads to Faraday rotation of the transmitted beam below T = 112 to 56 K for the 22 μm thick single crystal (c-axis orientation of 8π/18 relative to εX-rays) and sharp changes in the density of empty final states lead to zero transmitted radiation in …
Comparative Study Of Structural Properties Of Yba2cu3o7 Thin Films On Srtio3 Single Crystal And Bicrystal Substrates By X- Ray Diffraction, M. Navacerrada, A. Mehta, H. Sahibudeen, Juana Acrivos
Comparative Study Of Structural Properties Of Yba2cu3o7 Thin Films On Srtio3 Single Crystal And Bicrystal Substrates By X- Ray Diffraction, M. Navacerrada, A. Mehta, H. Sahibudeen, Juana Acrivos
Faculty Publications, Chemistry
We present a comparative study in terms of structural properties deduced from X - ray diffraction diagrams between YBa2Cu3O7 (YBCO) thin films fabricated on SrTiO3 (STO) single crystal substrates and bicrystallines substrates with a symmetrical tilt angle of 24 degrees. Periodic Lattice Distortions (PLD) have been observed around different Bragg peaks in YBCO thin films deposited on STO bicrystals while only diffraction peaks have been measured in the diagrams corresponding to the YBCO thin films deposited on STO single crystal substrates. Only in regions situated a 3.5 mm at both sides of the grain boundary the PDL have been investigated. …
Chemical Analysis By X-Ray Spectroscopy Near Phase Transitions In The Solid State, Juana Vivó Acrivos, L. Nguyen, T. Norman, C. T. Lin, W. Y. Liang, J. M. Honig, P Somasundaran
Chemical Analysis By X-Ray Spectroscopy Near Phase Transitions In The Solid State, Juana Vivó Acrivos, L. Nguyen, T. Norman, C. T. Lin, W. Y. Liang, J. M. Honig, P Somasundaran
Faculty Publications, Chemistry
The methods discussed in this work show that the types of changes which may be observed, by precise XAS measurements of Absorbance A versus temperature, across a phase transition are: the changes in the relaxation time of the final states due to fluctuations near a phase transition; the detection of the anomalous Bragg condition coupled to phonon modes XAS enhancement that identifies the temperature interval where the phonon modes are active, the symmetry changes which introduce new allowed transitions to finite states below an element edge, near Tc indicate what symmetry changes occur, and the method of XTDAFST0 = …
Spin-Exchange Term In The Solvent Equation Of State Near The Critical Point For Electron Transfer Reactions, Juana Vivó Acrivos
Spin-Exchange Term In The Solvent Equation Of State Near The Critical Point For Electron Transfer Reactions, Juana Vivó Acrivos
Faculty Publications, Chemistry
Phenomenological Equations of State (EOS) for fluids near their critical point have been obtained using literature compression factor data, Zc = Pc Vc/(n R Tc) = 0.40 to 0.10 in Table I (Pc, Vc/n, Tc are the pressure, volume per n mole, and the absolute temperature of the fluid at the critical point). The objective is to explain the deviations from the van der Waals value, Zc(vdW) = 3/8 (-70 % for molten Se and alkali metals up to 6 % for molten Pb, Hg, and In) by including in the commonly used phenomenological thermodynamic relations a term which explicitly …
Solid State Phase Transitions Characterized By Esr And Xas, Juana Vivó Acrivos
Solid State Phase Transitions Characterized By Esr And Xas, Juana Vivó Acrivos
Faculty Publications, Chemistry
Measurements of the relaxation time, of electron systems to a disturbance, by two different spectroscopic methods are examined in detail, with the purpose to establish how the presence of fluctuations near a solid state phase transition are made evident in insulators, conductors and superconductors. The absolute temperature and the relaxation time determine the thermodynamic stability of the electronic system near a phase transition by the Uncertainty Principle. At a given temperature T, Landau and Lifshitz obtain the stability from the lower limit of the uncertainty in entropy in units of the Boltzmann constant, S/kB << 1 when T >> 3.82 K ps. Magnetic resonance …<>
Dynamic Phenomena In Organic Metal (Bedt-Ttf)3ta2f11, Juana Acrivos
Dynamic Phenomena In Organic Metal (Bedt-Ttf)3ta2f11, Juana Acrivos
Faculty Publications, Chemistry
Dynamic electron spin resonance, ESR measurements suggest that this paramagnetic, layered organic metal behaves similarly to cuprate superconductors. There is a dynamic equilibrium between doublet, D and triplet, T* states near the transition temperature to superconductivity Tc= 10±3 K; antiferromagnetic, AF resonance is observed from room temperature to ≈ 150 K, in this temperature region the temperature dependence of the D Lorentzian ESR line widths obtains a first order rate constant for the disappearance of the state (k1 = 3.5 ×107 e−111/T/s) and T* ESR is not observed, it is detected only below 44 K when the lifetime of AF …
Dynamic Phenomena In Layer Superconducting Cuprate And Organic Metals, Juana Acrivos, Lei Chen, C. Burch
Dynamic Phenomena In Layer Superconducting Cuprate And Organic Metals, Juana Acrivos, Lei Chen, C. Burch
Faculty Publications, Chemistry
Dynamic electron spin resonance (ESR) and extended x-ray absorption edge fine structure (XAFS) measurements suggest that layered organic metals and cuprate superconductors behave similarly. The response to microwave radiation in a modulated external magnetic field indicates that: (i) triplet state, T * ESR is observed below Tc for both; (ii) the condensation of free spin doublet D to T* occurs above the transition temperature to superconductivity Tc (10 ± 1 K for the organic metal (BEDT-TTF)3Ta2F11 and 92 to 12 K for YBa2Cu3O7-δ and its rare earth derivatives); (iii) antiferomagnetic (AF) resonance is detected above Tc for the organic metal. …
Dynamic Phenomena In Superconducting Oxides By Esr, Juana Vivó Acrivos, Lei Chen, C. M. Burch, P. Metcalf, J. M. Honig, R. S. Liu, K. K. Singh
Dynamic Phenomena In Superconducting Oxides By Esr, Juana Vivó Acrivos, Lei Chen, C. M. Burch, P. Metcalf, J. M. Honig, R. S. Liu, K. K. Singh
Faculty Publications, Chemistry
Dynamic electron spin resonance (ESR) measurements compare the paramagnetic and antiferromagnetic (AF) properties of superconducting oxides in the range 4 K to room temperature, at 8 MHz and 9.36 GHz. Two are derivatives of YBa2Cu30 7: 1: Nd(Nd0.05Ba0.95 )2Cu30 7, Te0 =72 K and II: Y0.2Cao.8Sr2[Cu2(Tlo.5Pb0.5 )]07, Te0 =108 K and two are cases where AF ordering dominates the weak superconductivity: III: Nb01.1> 1. 25 ~Teo~ 10 K and IV: La2Ni04.00, 70 K :::: Teo:::: 40 K. At temperatures 298:::: T:::: 64 K, the ESR absorption by I indicates orthorhombic symmetry. The peaks at Ke =2.06, gb =2.13, and Ka …
Interaction Of Pyridine With Ba2casr2cu20x, Juana Acrivos, C. Lin
Interaction Of Pyridine With Ba2casr2cu20x, Juana Acrivos, C. Lin
Faculty Publications, Chemistry
The adsorption of of pyridine on single crystals of Bi2CaSr2Cu2Ox has been followed by optical microscopy on the crystal surface, where a blue solution is formed as a first step of reaction. The superconducting properties of the single crystal and its structure were monitored by ac susceptibility and by x-ray diffraction measurements. The results (as observed by the growth of the blue solution boundary versus time with Daa = 3.7x10-10 cm2/s.) indicate that the reaction starts at nucleation sites on the basal surface of the crystal. The edges of the crystal also show blue nucleation sites but these do not …
Esr Study Of Optically Induced Phase Transitions, Juana Vivó Acrivos, H. P. Hughes, S. S.P. Parkin
Esr Study Of Optically Induced Phase Transitions, Juana Vivó Acrivos, H. P. Hughes, S. S.P. Parkin
Faculty Publications, Chemistry
We have identified an optically enhanced magnetic phase transition in the newly synthesized organic molecular charge transfer salt, (BEDT-TTF)3Ta2F11 (BEDT-TTF bisethylenedithiolotetrathiafulvalene) by ESR absorption measurements in the X band microwave region. At room temperature, only a doublet state ESR absorption is observed, but below 30 K severa~ tripl~t E.SR absorpti_ons appear. The orientation dependence of the ESR absorption under lllummat10n at energies near the band gaps in the material ( 640 nm, T = 12 to 5 K H0 < 0.34 T) indicates that there are rapid spin exchange processes with times r < w-s; near 7 ~o 5 K.along cert~in ~rystallographic directions with a temperature dependen~e suggesting spm-lattlce relaxation times which proceed via Van Vleck "direct processes." This, to our knowledge, is the first case where the magnetic properties of a charge transfer salt are altered by the interaction with photons of energy equal to the band gaps in a low dimensional solid providing a new, interesting way to investigate these materials.
Nmr Measurements On Intercalated 3r-Tas2.Ix (I=Nh3 And N2h4), N. H. Handly, Juana Vivó Acrivos
Nmr Measurements On Intercalated 3r-Tas2.Ix (I=Nh3 And N2h4), N. H. Handly, Juana Vivó Acrivos
Faculty Publications, Chemistry
No abstract provided.
Xanes In (Tmtsef)2re04: Polarization Dependence Of The Se K-Edge, Juana Vivó Acrivos, S.S. P. Parkin
Xanes In (Tmtsef)2re04: Polarization Dependence Of The Se K-Edge, Juana Vivó Acrivos, S.S. P. Parkin
Faculty Publications, Chemistry
We have measured XANES (X-ray Absorption Near Edge Spectra) near the Re Li (i=l,II,III) edges in (TMTTF)2Re04 and (TMTSeF) 2Re04 and the Se K edge in the latter compound. An important dependence of the XANES at the Se K edge on the polarisation of the incident beam with respect to the crystal axes was observed, whose interpretation can give information on the symmetry of the unoccupied conduction band states. The positions of the Re L edges were compared with those in several inorganic compounds containing Re in various oxidation states, and were found to be, within experimental error, the same …
Measurement Of Synchrotron X-Ray Energies And Line Shapes Using Diffraction Markers, Juana Vivó Acrivos, S.S. P. Parkin, K. Hathaway, J. R. Reynolds, M. P. Klein, A. Thompson, D. Goodin
Measurement Of Synchrotron X-Ray Energies And Line Shapes Using Diffraction Markers, Juana Vivó Acrivos, S.S. P. Parkin, K. Hathaway, J. R. Reynolds, M. P. Klein, A. Thompson, D. Goodin
Faculty Publications, Chemistry
Standard reference markers for accurate, reproducible synchrotron x-ray energies are obtained using a three Si crystal spectrometer. The first two crystals are in the monochromator and the third is used to obtain diffraction markers which monitor the energy. Then for any value of the glancing angle on the reference Si crystal the energy for the (333) diffraction must occur at 3/4 that of the (444) and 3/5 of that for the (555). This establishes for the first time an absolute synchrotron energy scale. Higher-order diffractions are used to determine excitation line profiles. We conclude that the use of reference diffractions …
Effects Of N2h4 On The Transition Temperature In The Anisotropic Superconductor Tase3, K. Yamaya, T. H. Geballe, Juana Vivó Acrivos, J. Code
Effects Of N2h4 On The Transition Temperature In The Anisotropic Superconductor Tase3, K. Yamaya, T. H. Geballe, Juana Vivó Acrivos, J. Code
Faculty Publications, Chemistry
No abstract provided.
Conduction Band Symmetry In Ta Chalcogenides From Ta L Edge X-Ray Absorption Spectroscopy (Xas), Juana Vivó Acrivos, S.S. P. Parkin, J. Code, J. Reynolds, K. Hathaway, H. Kurasaki, E. Marseglia
Conduction Band Symmetry In Ta Chalcogenides From Ta L Edge X-Ray Absorption Spectroscopy (Xas), Juana Vivó Acrivos, S.S. P. Parkin, J. Code, J. Reynolds, K. Hathaway, H. Kurasaki, E. Marseglia
Faculty Publications, Chemistry
No abstract provided.
Mott G-Ratios In Rbx(Nh3)1-X And Oxidation State Of Rubidium Compounds From Xas, Juana Vivó Acrivos, K. Hathaway, A. Robertson, M. P. Klein, A. Thompson
Mott G-Ratios In Rbx(Nh3)1-X And Oxidation State Of Rubidium Compounds From Xas, Juana Vivó Acrivos, K. Hathaway, A. Robertson, M. P. Klein, A. Thompson
Faculty Publications, Chemistry
The x-ray absorption spectra (XAS) of Rb metal, Rh,("JH,J, ,, 2H-NbSe2Rb111x and RbBr near the Rb K-edge have been used to ascertain that the oxidation state V of rubidium dissolved in ammonia and intt:rcalated in the layer compound is in the range 0 < V < I. Theobservededge shifts with temperature for semimctals are explainedin terms of the population of band states, and the ratio of the density states near the mobility edge over that calculated for a free electron model, i.e. the Mott ratio g, is ascertained using a semiempirical relation developed for the x-ray absorbance from Is levels to empty states ncar the mobility edge.
In Situ Intercalation Of Tas2 In The Electron Microscope, G. Tatlock, Juana Acrivos
In Situ Intercalation Of Tas2 In The Electron Microscope, G. Tatlock, Juana Acrivos
Faculty Publications, Chemistry
Electron diffraction had been used to study the formation of a variety of complex superlattices in the 1T, 2H and 4Hb polytypes of TaS2 during intercalation with hydrazine gas (N2H4), in situ in the electron microscope. Results are presented over the temperature range 15K-360K and are interpreted in terms of scattering from periodic lattice distortions linked to charge density waves. Comparisons are also made with similar effects in both the as-grown crystals and the TaS2 samples containing other adducts.
Properties Of Intercalated 2h-Nbse2, 4hb-Tas2 And 1t-Tas2, S. F. Meyer, R. E. Howard, G. R. Stewart, Juana Vivó Acrivos, T. H. Geballe
Properties Of Intercalated 2h-Nbse2, 4hb-Tas2 And 1t-Tas2, S. F. Meyer, R. E. Howard, G. R. Stewart, Juana Vivó Acrivos, T. H. Geballe
Faculty Publications, Chemistry
The layered compounds 2H-NbSe, 24Hb-TaS, 2and 1T-TaS2 have been intercalated with organic molecules; and the resulting crystal structure, heat capacity, conductivity, and superconductivity have been studied. The coordination in the disulfide layers was found to be unchanged in the product phase. Resistance minima appear and the superconducting transition temperature is reduced in the NbSe2 complex. Conversely, superconductivity is induced in the 4Hb-TaS2 complex. Corresponding evidence of a large change of the density of states, negative for 2H-NbSe2 and positive for 4Hb-TaS2, was also observed upon intercalation. The transport properties of all the intercalation complexes show a pronounced dependence upon the …
Properties Of Hxtas2, D. W. Murphy, F. J. Disalvo, G. W. Hull, J. V. Waszczak, S. F. Meyers, G. R. Stewart, S. Early, Juana Vivó Acrivos, T. H. Geballe
Properties Of Hxtas2, D. W. Murphy, F. J. Disalvo, G. W. Hull, J. V. Waszczak, S. F. Meyers, G. R. Stewart, S. Early, Juana Vivó Acrivos, T. H. Geballe
Faculty Publications, Chemistry
The preparation of Hx TaS2 (0 < x < 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly Hp in air). Magnetic susceptibility data show that a low temperature transformation in 2H ... TaS2 (at so•K) is suppressed with the addition of hydrogen, and· at the same time the superconducting transition temperature T c rises from 0.8 to ~4.2•K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and T c measurements in other intercalation compounds, we suggest that the rise of T c (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity.
Optical Studies Of Metal- Semiconductor Transmutations Produced By Intercalation, Juana Vivó Acrivos, Y. Liang, J. Wilson, A. Yoffe
Optical Studies Of Metal- Semiconductor Transmutations Produced By Intercalation, Juana Vivó Acrivos, Y. Liang, J. Wilson, A. Yoffe
Faculty Publications, Chemistry
Spectra of the alkali metal intercalation products of MoS2 and NbSc2 arc interpreted in terms of a previously published band model.
Resonance Absorption Of P-Benzosemiquinone In The Zeeman Region, Juana Vivó Acrivos
Resonance Absorption Of P-Benzosemiquinone In The Zeeman Region, Juana Vivó Acrivos
Faculty Publications, Chemistry
No abstract provided.
Spin-Resonance Transitions Of Free Radicals In The Zeeman Region, Juana Vivó Acrivos
Spin-Resonance Transitions Of Free Radicals In The Zeeman Region, Juana Vivó Acrivos
Faculty Publications, Chemistry
No abstract provided.
Application Of The Sideband Technique To Wide-Line Nmr Spectra, Juana Vivó Acrivos
Application Of The Sideband Technique To Wide-Line Nmr Spectra, Juana Vivó Acrivos
Faculty Publications, Chemistry
No abstract provided.
Analysis Of The A3(X3)3 Nuclear Spin System And -Electron Coupled Hyperfine Splitting Constants In Aromatic Hydrocarbons, Juana Acrivos
Analysis Of The A3(X3)3 Nuclear Spin System And -Electron Coupled Hyperfine Splitting Constants In Aromatic Hydrocarbons, Juana Acrivos
Faculty Publications, Chemistry
The nuclear spin functions for the A3(X3)3 system have been developed and used to analyse the NMR spectra of (CH3)3C6H3 and (CF3)3C6H3. The π-electron coupled hyperfine splitting constants, obtained from the Ramsey theory with simple Hückel M.O.'s for benzene and without the assumption of an average energy of excitation for the virtual processes which give rise to the coupling, are in agreement with the hyperfine constants observed between the methyl groups and the ring protons in the above compounds.