SIGNATURE OF LOCAL STRUCTURE ANOMALY AT Tc IN THE Nb3Ge SUPERCONDUCTOR

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1713-1719 ◽  
Author(s):  
M. FILLIPPI ◽  
N. L. SAINI ◽  
H. OYANAGI ◽  
A. BIANCONI
Keyword(s):  
Local Structure ◽  
Cuprate Superconductors ◽  
Waller Factor ◽  
Superconducting Transition ◽  
Temperature Dependent ◽  
Local Electron ◽  
Atomic Displacements ◽  
Debye Waller Factor ◽  
The One ◽  
X Ray Absorption

We report local structure of Nb3Ge intermetallic superconductor by Ge K-edge extended X-ray absorption fine structure (EXAFS) measurements performed in the temperature range of 6–300 K, with an emphasis to determine the local and instantaneous atomic displacements across the superconducting transition temperature T c . We find that the temperature dependent correlated Debye–Waller factor of the Ge-Nb bonds shows a drop at the T c while cooling the sample, similar to the one observed in the high-T c cuprate superconductors. The results provide a clear indication of an intimacy between the local atomic displacements and the short coherence superconductivity, and suggests that local electron-lattice interaction should be considered to explain the high-T c superconductivity in these materials.

Temperature-dependent atomic B factor: an ab initio calculation

2019 ◽  
Vol 75 (4) ◽  
pp. 624-632 ◽  
Author(s):  
Cristiano Malica ◽  
Andrea Dal Corso
Keyword(s):  
Ab Initio ◽  
Harmonic Approximation ◽  
Debye Model ◽  
Waller Factor ◽  
Temperature Dependent ◽  
Atomic Displacements ◽  
Debye Waller Factor ◽  
Diffraction Peaks ◽  
Effects Of Temperature ◽  
Quantum Espresso

The Debye–Waller factor explains the temperature dependence of the intensities of X-ray or neutron diffraction peaks. It is defined in terms of the B matrix whose elements B αβ are mean-square atomic displacements in different directions. These quantities, introduced in several contexts, account for the effects of temperature and quantum fluctuations on the lattice dynamics. This paper presents an implementation of the B factor (8π2 B αβ) in the thermo_pw software, a driver of Quantum ESPRESSO routines that provides several thermodynamic properties of materials. The B factor can be calculated from the ab initio phonon frequencies and displacements or can be estimated, although less accurately, from the elastic constants, using the Debye model. The B factors are computed for a few elemental crystals: silicon, ruthenium, magnesium and cadmium; the harmonic approximation at fixed geometry is compared with the quasi-harmonic approximation where the B factors are calculated accounting for thermal expansion. The results are compared with the available experimental data.

Study on Effects of Heavy Ion Irradiation on CeO2 by Using Synchrotron Radiation X-Ray Absorption Spectroscopy -as a Simulation Study for Radiation Damage in High-Burnup Light Water Reactor Fuels-

2007 ◽  
Vol 1043 ◽  
Author(s):  
Hirotaka Ohno ◽  
Daiju Matsumura ◽  
Yasuo Nishihata ◽  
Jun'ichiro Mizuki ◽  
Norito Ishikawa ◽  
...  
Keyword(s):  
Thin Films ◽  
Synchrotron Radiation ◽  
Ion Irradiation ◽  
Heavy Ion ◽  
Waller Factor ◽  
X Ray ◽  
Debye Waller Factor ◽  
Atomic Distance ◽  
Exafs Measurement ◽  
X Ray Absorption

AbstractCeO2 thin films were irradiated with 200MeV Xe ions. Effects of the irradiation were studied by using Extended X-ray Absorption Fine Structure (EXAFS) measurement at SPring8 synchrotron radiation facility. EXAFS spectra for the irradiated thin films near the Ce K-edge show that the coordination number for oxygen atoms around Ce atom decreases and that the Ce-O Debye-Waller factor increases by the irradiation. The atomic distance between oxygen atom and Ce atom does not vary within the accuracy of EXAFS measurement. The effect of high density electronic excitation on the structure of CeO2 is discussed.

ISOTOPIC EFFECT IN DEBYE–WALLER FACTOR OF CRYSTALLINE GERMANIUM

2013 ◽  
Vol 27 (26) ◽  
pp. 1350191
Author(s):  
HO KHAC HIEU ◽  
VU VAN HUNG
Keyword(s):  
Lattice Dynamics ◽  
Mass Difference ◽  
Relative Displacement ◽  
Waller Factor ◽  
Isotopic Effect ◽  
Mean Square ◽  
X Ray ◽  
Debye Waller Factor ◽  
X Ray Absorption ◽  
Crystalline Germanium

The statistical moment method has been used to study the effect of isotopic mass difference on extended X-ray absorption fine structure (EXAFS) Debye–Waller factor of crystalline germanium. The effects on the parallel mean-square relative displacement and the atomic mean square displacements have been considered. This research also exposed that isotopic effect is noticeable where the correlated atomic motion is concerned. Numerical calculations have been performed for two isotopes 70 Ge and 76 Ge in range of temperature from 0 K to 600 K. Our results are compared with available experimental EXAFS data [J. Purans et al., Phys. Rev. Lett.100 (2008) 055901] as well as with lattice dynamics calculations [A. Sanson, Solid State Sci.12 (2010) 1988] and the good agreements are found.

ELECTRONIC THEORY FOR ELECTRON-DOPED CUPRATE SUPERCONDUCTORS: d-WAVE SUPERCONDUCTIVITY AND THE PHASE DIAGRAM

2000 ◽  
Vol 14 (29n31) ◽  
pp. 3555-3560
Author(s):  
D. MANSKE ◽  
I. EREMIN ◽  
K. H. BENNEMANN
Keyword(s):  
Cuprate Superconductors ◽  
Narrow Range ◽  
Spin Fluctuation ◽  
Flat Band ◽  
Superconducting Transition ◽  
Phonon Interaction ◽  
Pairing Mechanism ◽  
Lattice Disorder ◽  
Electron Phonon Interaction ◽  
The One

Using the one-band Hubbard Hamiltonian we determine various basic properties of the electron-doped cuprate superconductor Nd 2-x Ce x CuO 4 for a spin-fluctuation-induced pairing mechanism. We find a narrow range of superconductivity and, most importantly, like for hole-doped cuprates dx2-y2 -symmetry for the superconducting order parameter. The superconducting transition temperatures Tc(x) for various electron doping concentrations x are calculated to be much smaller than for hole-doped cuprates due to the different energy dispersion and a flat band well below the Fermi level. We find that lattice disorder may sensitively distort the dx2-y2 -symmetry via electron-phonon interaction yielding a finite isotope exponent α0.

Theory of the Normal State of Cuprate Superconductors

1989 ◽  
Vol 169 ◽  
Author(s):  
Philip W. Anderson ◽  
Yong Ren
Keyword(s):  
Fermi Surface ◽  
Normal State ◽  
Cuprate Superconductors ◽  
Metallic State ◽  
Zero Energy ◽  
Temperature Dependent ◽  
Spin Excitations ◽  
Photoemission Data ◽  
The One ◽  
Do So

AbstractWe propose a framework for the theory of the "normal" metallic state of the CuO2 planes of high Tc superconductors. This state is closely analogous to the known state of the one-dimensional Hubbard model, with spin excitations which can be thought of as chargeless (Z = 0) Fermions occupying the interior of the conventional Fermi surface, and charged excitations which have zero energy near the spanning vectors 2kF of that Fermi surface. The electron spectrum is the composite spectrum of two of these excitations, and can be fitted to angle-resolved photoemission data. When we do so we can calculate or estimate many properties of the normal state in excellent agreement with experiment, and show that the pair susceptibility is anomalously large and temperature-dependent, explaining the high Tc and the specific heat behavior.

Study of Co-Cr Mixed Oxides for Different Applications

2017 ◽  
Vol 68 (9) ◽  
pp. 2039-2042
Author(s):  
Vasile Georgescu ◽  
Gabriel Vasilievici ◽  
Mihaela Bombos ◽  
Casen Panaitescu
Keyword(s):  
Thermal Analysis ◽  
Solid Solution ◽  
Local Structure ◽  
Mixed Oxides ◽  
Magnetic Measurements ◽  
Waller Factor ◽  
Oxide System ◽  
Ir Spectrometry ◽  
Debye Waller Factor ◽  
Metallic Cations

Mixture metal oxide system Co-Cr were prepared by decomposition of the precursor complexes obtained from a mixture Co-Cr nitrates with tartaric acid. The samples were subsequently submitted to chemical analysis, magnetic measurements, IR spectrometry, UV-Vis, thermal analysis, XRD, EXAFS and TPR. At 600oC was identificated a solid solution of CoCr2O4 with Co3O4. With Cu-CrK-edge EXAFS the local structure of samples calcinated of 420oC and 600oC was obtained. By theirs analysis was calculated: the lengths of M-O bounds, number of coordination (N), Debye-Waller factor (A1) and x metallic cations fraction in tetrahedral structures (spinelic centers). The TPR measurements were emphasized the existence of two reduction cycles.

Evolution of the Nanostructure of Giant Magnetoresistance Heterogeneous Alloys CoxAg1-x Upon Annealing

1995 ◽  
Vol 400 ◽  
Author(s):  
J. R. Regnard ◽  
C. Revenant-Brizard ◽  
B. Dieny ◽  
B. Mevel ◽  
J. Mimault
Keyword(s):  
Giant Magnetoresistance ◽  
Annealing Temperature ◽  
Liquid Nitrogen Temperature ◽  
Waller Factor ◽  
Total Electron Yield ◽  
Total Electron ◽  
X Ray ◽  
Debye Waller Factor ◽  
X Ray Absorption ◽  
Heterogeneous Alloys

AbstractHeterogeneous alloys CoxAg1-x with atomic concentrations x=0.20 and 0.35, presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Co K edge after annealings at various temperatures. For both sample concentrations, the Co atoms are mainly in small filament agglomerates for the as-deposited and low temperature annealed samples (T<150°C). In this temperature range, the local Co atomic environment is very stable and disordered. A structural change has been detected by XANES and EXAFS analysis between the 250 and 400°C annealings. After a 400°C annealing during 10 min, the nanostructures evolve towards larger, more compact and well ordered granules. The Co-Co distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicating that the small filament-shaped agglomerates are under strain in the Ag matrix. The Debye-Waller factor of the Co0.35Ag0.65 samples decreases continously as the annealing temperature increases, as this factor drops suddenly after a 250°C annealing for the Co0.20Ag0.80 sample. The Co agglomeration is steadily larger for the Co0.35Ag0.65 sample than for the Co0.20Ag0.80 one. The Co-Ag contribution is negligible for the Co0.35Ag0.65 sample, as it represents approximately one third of the nearest neighbors for the Co0.20Ag0.80 sample from the as-deposit up to a 250°C annealing stage.

X-ray absorption of bromonaphthalene dissolved in supercritical fluid xenon

1998 ◽  
Vol 5 (3) ◽  
pp. 1004-1006 ◽  
Author(s):  
T. Murata ◽  
K. Nakagawa ◽  
Y. Otsuki ◽  
I. Shimoyama ◽  
T. Mizutani ◽  
...  
Keyword(s):  
Absorption Spectrum ◽  
Supercritical Fluid ◽  
Large Degree ◽  
Waller Factor ◽  
Pure Liquid ◽  
High Pressure Cell ◽  
X Ray ◽  
Debye Waller Factor ◽  
X Ray Absorption ◽  
Best Fit

The results of Br K-edge X-ray absorption measurements of 1-bromonaphthalene dissolved in supercritical fluid Xe are reported. As the pressure of Xe confined in a high-pressure cell is increased, the absorption spectrum of bromonaphthalene gradually appears, showing that Xe in the supercritical fluid state solvates the bromonaphthalene molecule. The spectrum of the dissolved sample shows a remarkable difference from that of the pure liquid sample in the near-edge region of the X-ray absorption spectrum, reflecting the interaction of the solute material with solvent Xe. Ab initio full multiple-scattering calculations can reproduce the spectral features qualitatively. A large value of the Debye–Waller factor must be introduced to give the best fit, corresponding to a large degree of spatial disorder and violent thermal vibration of the Xe atoms around the Br atom.

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