224 research outputs found
Pressure-induced lattice instabilities and superconductivity in YBa2Cu4O8 and optimally doped YBa2Cu3O7-{\delta}
Combined synchrotron angle-dispersive powder diffraction and micro-Raman
spectroscopy are used to investigate the pressure-induced lattice instabilities
that are accompanied by T anomalies in YBaCuO, in comparison with the optimally doped YBaCuO and the non-superconducting PrBaCuO. In the first two superconducting systems there is a clear
anomaly in the evolution of the lattice parameters and an increase of lattice
disorder with pressure, that starts at as well as
irreversibility that induces a hysteresis. On the contrary, in the Pr-compound
the lattice parameters follow very well the expected equation of state (EOS) up
to 7 GPa. In complete agreement with the structural data, the micro-Raman data
of the superconducting compounds show that the energy and width of the A phonons show anomalies at the same pressure range where the lattice
parameters deviate from the EOS and the average Cu2-O bond length
exhibits a strong contraction and correlate with the non-linear pressure
dependence of T. This is not the case for the non superconducting Pr
sample, clearly indicating a connection with the charge carriers. It appears
that the cuprates close to optimal doping are at the edge of lattice
instability.Comment: 6 pages, 7 figure
Lattice effects in the LaSrCuO compounds
Systematic Raman studies on several cuprates (YBaCuO, YBaCuO or BiSrCaCuO) have shown that at optimal doping the compounds
are at the edge of lattice instability; once this level is exceeded, by means
of doping or applying external hydrostatic pressure, the changes in the
transition temperature are accompanied by spectral modifications. There are
strong indications that the reduction in T is correlated with a
separation into nanoscale phases, which involve the oxygen atoms of the
CuO planes. In this work, modifications with doping in the Raman
spectra of the LaSrCuO compound are presented,
which show that spin or charge ordering is coupled with lattice distortions in
the whole doping region.Comment: 6 pages, 6 figure
Brain–computer interfacing with interactive systems-Case study 2
info:eu-repo/semantics/publishedVersio
Sc substitution for Mg in MgB2: effects on Tc and Kohn anomaly
Here we report synthesis and characterization of Mg_{1-x}Sc_{x}B_{2}
(0.12T_{c}>6 K.
We find that the Sc doping moves the chemical potential through the 2D/3D
electronic topological transition (ETT) in the sigma band where the ``shape
resonance" of interband pairing occurs. In the 3D regime beyond the ETT we
observe a hardening of the E_{2g} Raman mode with a significant line-width
narrowing due to suppression of the Kohn anomaly over the range 0<q<2k_{F}.Comment: 8 pages, 4 EPS figures, to be published in Phys. Rev.
Crystal Structure Studies of Human Dental Apatite as a Function of Age
Studies of the average crystal structure properties of human dental apatite
as a function of the tooth-age in the range of 5-87 years are reported. The
crystallinity of the dental hydroxyapatite decreases with the tooth-age. The
a-lattice constant that is associated with the carbonate content in carbonate
apatite decreases with the tooth-age in a systematic way, whereas the c-lattice
constant does not change significantly. Thermogravimetric measurements
demonstrate an increase of the carbonate content with the tooth-age. FTIR
spectroscopy reveals both, B and A-type carbonate substitutions with the B-type
greater than the A-type substitution by a factor up to ~5. An increase of the
carbonate content as a function of the tooth-age can be deduced from the ratio
of the v2 CO3 to the v1 PO4 IR modes.Comment: 17 page
Lattice anomalies in the FeAs tetrahedra of the NdFeAsO superconductor that disappear at T
High resolution synchrotron X-ray powder diffraction (SXRPD) was used to
study the temperature dependence of the oxygen deficient NdFeAsO
superconducting compound. By employing a dense temperature sampling we have
managed to reveal unnoticed structural modifications that start around
180K, and disappear at the transition temperature. The data show minor
changes of the structural characteristics in the Nd-O charge reservoir layer
while in the superconducting Fe-As layer the FeAs tetrahedron shows
gradual modifications below 180K, which suddenly disappear at T
strongly indicating a connection with superconductivity.Comment: 4 pages, 1 table, 5 figure
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