397 research outputs found
High pressure synthesis of FeO-ZnO solid solutions with rock salt structure: in situ X-ray diffraction studies
X-ray diffraction with synchrotron radiation has been used for the first time
to study chemical interaction in the FeO-ZnO system at 4.8 GPa and temperatures
up to 1300 K. Above 750 K, the chemical reaction between FeO and ZnO has been
observed that resulted in the formation of rock salt (rs) Fe1-xZnxO solid
solutions (0.3 \leq x \leq 0.85). The lattice parameters of these solid
solutions have been in situ measured as a function of temperature under
pressure, and corresponding thermal expansion coefficients have been
calculated.Comment: 9 pages, 2 figures, 1 tabl
Anomalous In-Plane Anisotropy of the Onset of Superconductivity in (TMTSF)2ClO4
We report the magnetic field-amplitude and field-angle dependence of the
superconducting onset temperature Tc_onset of the organic superconductor
(TMTSF)2ClO4 in magnetic fields H accurately aligned to the conductive ab'
plane. We revealed that the rapid increase of the onset fields at low
temperatures occurs both for H // b' and H // a, irrespective of the carrier
confinement. Moreover, in the vicinity of the Pauli limiting field, we report a
shift of a principal axis of the in-plane field-angle dependence of Tc_onset
away from the b' axis. This feature may be related to an occurrence of
Fulde-Ferrell-Larkin-Ovchinnikov phases.Comment: 4 pages, 4 figure
Search for solar axions in XMASS, a large liquid-xenon detector
XMASS, a low-background, large liquid-xenon detector, was used to search for
solar axions that would be produced by bremsstrahlung and Compton effects in
the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent
limit on the coupling for mass 1keV is
(90% C.L.), which is a factor of two stronger than the existing experimental
limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are
1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced
the most stringent limit, which is better than that previously derived from
astrophysical arguments regarding the Sun to date
Pressure induced high-spin to low-spin transition in FeS evidenced by x-ray emission spectroscopy
We report the observation of the pressure-induced high-spin to low-spin
transition in FeS using new high-pressure synchrotron x-ray emission
spectroscopy techniques. The transition is evidenced by the disappearance of
the low-energy satellite in the Fe K emission spectrum of FeS. Moreover,
the phase transition is reversible and closely related to the structural phase
transition from a manganese phosphide-like phase to a monoclinic phase. The
study opens new opportunities for investigating the electronic properties of
materials under pressure.Comment: ReVTeX, 4 pages, 3 figures inserted with epsfig. minor modifications
before submission to PR
Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4
We have studied the onset temperature of the superconductivity Tc_onset of
the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction
of the magnetic field H. We compare the results of two samples with nearly the
same onset temperature but with different scattering relaxation time tau. We
revealed a complicated interplay of a variety of pair-breaking effects and
mechanisms that overcome these pair-breaking effects. In low fields, the linear
temperature dependences of the onset curves in the H-T phase diagrams are
governed by the orbital pair-breaking effect. The dips in the in-plane
field-angle phi dependence of Tc_onset, which were only observed in the
long-tau sample, provides definitive evidence that the field-induced
dimensional crossover enhances the superconductivity if the field direction is
more than about 19-degrees away from the a axis. In the high-field regime for
H//a, the upturn of the onset curve for the long-tau sample indicates a new
superconducting state that overcomes the Pauli pair-breaking effect but is
easily suppressed by impurity scatterings. The Pauli effect is also overcome
for H//b' by a realization of another state for which the maximum of
Tc_onset(phi) occurs in a direction different from the crystalline axes. The
effect on Tc_onset of tilting the applied field out of the conductive plane
suggests that the Pauli effect plays a significant role in determining
Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4
is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77,
2008
Universal phase transitions of B1 structured stoichiometric transition-metal carbides
The high-pressure phase transitions of B1-structured stoichiometric
transition metal carbides (TMCs, TM=Ti, Zr, Hf, V, Nb, and Ta) were
systematically investigated using ab initio calculations. These carbides
underwent universal phase transitions along two novel phase-transition routes,
namely, B1\rightarrowdistorted TlI (TlI')\rightarrowTlI and/or
B1\rightarrowdistorted TiB (TiB')\rightarrowTiB, when subjected to pressures.
The two routes can coexist possibly because of the tiny enthalpy differences
between the new phases under corresponding pressures. Four new phases result
from atomic slips of the B1-structured parent phases under pressure. After
completely releasing the pressure, taking TiC as a representative of TMCs, only
its new TlI'-type phase is mechanically and dynamically stable, and may be
recovered.Comment: [email protected]
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