51 research outputs found
Friedel Oscillations and Charge-density Waves Pinning in Quasi-one-dimensional Conductors: An X-ray Access
We present an x-ray diffraction study of the Vanadium-doped blue bronze
K0.3(Mo0.972V0.028)O3. At low temperature, we have observed both an intensity
asymmetry of the +-2kF satellite reflections relative to the pure compound, and
a profile asymmetry of each satellite reflections. We show that the profile
asymmetry is due to Friedel oscillation around the V substituant and that the
intensity asymmetry is related to the charge density wave (CDW) pinning. These
two effects, intensity and profile asymmetries, gives for the first time access
to the local properties of CDW in disordered systems, including the pinning and
even the phase shift of FOs.Comment: 4 pages REVTEX, 5 figure
Evidence of a structural anomaly at 14 K in polymerised CsC60
We report the results of a high-resolution synchrotron X-ray powder
diffraction study of polymerised CsC in the temperature range 4 to 40 K.
Its crystal structure is monoclinic (space group I2/m), isostructural with
RbC. Below 14 K, a spontaneous thermal contraction is observed along
both the polymer chain axis, and the interchain separation along [111],
. This structural anomaly could trigger the occurrence of the spin-singlet
ground state, observed by NMR at the same temperature.Comment: 8 pages, 5 figures, submitte
X-ray spectrum of a pinned charge density wave
We calculate the X-ray diffraction spectrum produced by a pinned charge
density wave (CDW). The signature of the presence of a CDW consists of two
satellite peaks, asymmetric as a consequence of disorder. The shape and the
intensity of these peaks are determined in the case of a collective weak
pinning using the variational method. We predict divergent asymmetric peaks,
revealing the presence of a Bragg glass phase. We deal also with the long range
Coulomb interactions, concluding that both peak divergence and anisotropy are
enhanced. Finally we discuss how to detect experimentally the Bragg glass phase
in the view of the role played by the finite resolution of measurements.Comment: 13 pages 10 figure
Theory of Distinct Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs: the Specific Role of Alkalis
The polymer phases of AC60 form distinct crystal structures characterized by
the mutual orientations of the (C60-)n chains. We show that the direct electric
quadrupole interaction between chains always favors the orthorhombic structure
Pmnn with alternating chain orientations. However the specific quadrupolar
polarizability of the alkali metal ions leads to an indirect interchain
coupling which favors the monoclinic structure I2/m with equal chain
orientations. The competition between direct and indirect interactions explains
the structural difference between KC60 and RbC60, CsC60.Comment: 4 pages, 2 figures, 1 tabl
Optical investigation of the charge-density-wave phase transitions in
We have measured the optical reflectivity of the quasi
one-dimensional conductor from the far infrared up to the
ultraviolet between 10 and 300 using light polarized along and normal to
the chain axis. We find a depletion of the optical conductivity with decreasing
temperature for both polarizations in the mid to far-infrared region. This
leads to a redistribution of spectral weight from low to high energies due to
partial gapping of the Fermi surface below the charge-density-wave transitions
at 145 K and 59 K. We deduce the bulk magnitudes of the CDW gaps and discuss
the scattering of ungapped free charge carriers and the role of fluctuations
effects
Structural resolution of inorganic nanotubes with complex stoichiometry.
Determination of the atomic structure of inorganic single-walled nanotubes with complex stoichiometry remains elusive due to the too many atomic coordinates to be fitted with respect to X-ray diffractograms inherently exhibiting rather broad features. Here we introduce a methodology to reduce the number of fitted variables and enable resolution of the atomic structure for inorganic nanotubes with complex stoichiometry. We apply it to recently synthesized methylated aluminosilicate and aluminogermanate imogolite nanotubes of nominal composition (OH)3Al2O3Si(Ge)CH3. Fitting of X-ray scattering diagrams, supported by Density Functional Theory simulations, reveals an unexpected rolling mode for these systems. The transferability of the approach opens up for improved understanding of structure-property relationships of inorganic nanotubes to the benefit of fundamental and applicative research in these systems
Diffraction techniques and vibrational spectroscopy opportunities to characterise bones
From a histological point of view, bones that allow body mobility and protection of internal organs consist not only of different organic and inorganic tissues but include vascular and nervous elements as well. Moreover, due to its ability to host different ions and cations, its mineral part represents an important reservoir, playing a key role in the metabolic activity of the organism. From a structural point of view, bones can be considered as a composite material displaying a hierarchical structure at different scales. At the nanometre scale, an organic part, i.e. collagen fibrils and an inorganic part, i.e. calcium phosphate nanocrystals are intimately mixed to assure particular mechanical properties
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