28 research outputs found
Manganite charge and orbitally ordered and disordered states probed by Fe substitution into Mn site in LnBaMn1.96Fe0.04O5, LnBaMn1.96Fe0.04O6 and LnBaMn1.96Fe0.04O5.5 (Ln=Y, Gd, Sm, Nd, Pr, La)
The layered manganese oxides LnBaMn1.96Fe0.04Oy (Ln=Y, Gd, Sm, Nd, Pr, La)
have been synthesized for y=5, 5.5 and 6. In the oxygen-saturated state (y=6)
they exhibit the charge and orbital order at ambient temperature for Ln=Y, Gd,
Sm, but unordered eg-electronic system for Ln=La,Pr,Nd. Fourfold increase of
quadrupole splitting was observed owing to the charge and orbital ordering.
This is in agreement with the jumplike increase in distortion of the reduced
perovskite-like cell for the charge and orbitally ordered manganites compared
to the unordered ones. Substitution of 2 percents of Mn by Fe suppresses the
temperatures of structural and magnetic transitions by 20 to 50 K. Parameters
of the crystal lattices and the room-temperature M\"{o}ssbauer spectra were
studied on forty samples whose structures were refined within five symmetry
groups: P4/mmm, P4/nmm, Pm-3m, Icma and P2/m. Overwhelming majority of the Fe
species are undifferentiated in the M\"{o}ssbauer spectra for most of the
samples. Such the single-component spectra in the two-site structures are
explained by the preference of Fe towards the site of Mn(III) and by the
segmentation of the charge and orbitally ordered domains.Comment: 8 figures; figures 2 and 3 were revise
3D-XY critical fluctuations of the thermal expansivity in detwinned YBa2Cu3O7-d single crystals near optimal doping
The strong coupling of superconductivity to the orthorhombic distortion in
YBa2Cu3O7-d makes possible an analysis of the superconducting fluctuations
without the necessity of subtracting any background. The present
high-resolution capacitance dilatometry data unambiguously demonstrate the
existence of critical, instead of Gaussian, fluctuations over a wide
temperature region (+/- 10 K) around Tc. The values of the amplitude ratio
A+/A-=0.9-1.1 and the leading scaling exponent |alpha|<0.018, determined via a
least-squares fit of the data, are consistent with the 3D-XY universality
class. Small deviations from pure 3D-XY behavior are discussed.Comment: 11 pages including three figure
Dilution and clustering of Fe in the rutile phases of TiO2 and SnO2
ABSTRACT: Dilute magnetic semiconductors of Fe-doped SnO2 and TiO2 with the structure of rutile were prepared in forms of powder and thin films using the techniques of sol gel and pulsed-laser deposition. We present the results of measurement of vibrational density of states of Fe impurity dopants in these oxides and demonstrate the cases of dilution and clustering. The oxygen pressure during the film deposition was varied between 10−1 and 10−8 Torr. In TiO2 films made at 10−1 Torr, Fe is diluted, however, in films made at 10−8 Torr Fe is clustered. The case of true Fe dilution in SnO2 is also shown. In spite of larger mass defect for Fe in SnO2 than that for Fe in TiO2 the dilute Fe species probe the phonon states in SnO2 more faithfully than in TiO2. This result is understood in terms of the combined effect of mass defect and nearest-neighbor force-constant changes. The impurity modes are more pronounced in TiO2 than in SnO2 due to ca. 10% difference of the lattice cell volumes between these two rutile oxides
Anomalously large oxygen-ordering contribution to the thermal expansion of untwinned YBa2Cu3O6.95 single crystals: a glass-like transition near room temperature
We present high-resolution capacitance dilatometry studies from 5 - 500 K of
untwinned YBa2Cu3Ox (Y123) single crystals for x ~ 6.95 and x = 7.0. Large
contributions to the thermal expansivities due to O-ordering are found for x ~
6.95, which disappear below a kinetic glass-like transition near room
temperature. The kinetics at this glass transition is governed by an energy
barrier of 0.98 +- 0.07 eV, in very good agreement with other O-ordering
studies. Using thermodynamic arguments, we show that O-ordering in the Y123
system is particularly sensitive to uniaxial pressure (stress) along the chain
axis and that the lack of well-ordered chains in Nd123 and La123 is most likely
a consequence of a chemical-pressure effect.Comment: 4 pages, 3 figures, submitted to PR
Forward Neutral Pion Transverse Single Spin Asymmetries in p+p Collisions at \sqrt{s}=200 GeV
We report precision measurements of the Feynman-x dependence, and first
measurements of the transverse momentum dependence, of transverse single spin
asymmetries for the production of \pi^0 mesons from polarized proton collisions
at \sqrt{s}=200 GeV. The x_F dependence of the results is in fair agreement
with perturbative QCD model calculations that identify orbital motion of quarks
and gluons within the proton as the origin of the spin effects. Results for the
p_T dependence at fixed x_F are not consistent with pQCD-based calculations.Comment: 6 pages, 4 figure
Indications of Conical Emission of Charged Hadrons at the BNL Relativistic Heavy Ion Collider
Three-particle azimuthal correlation measurements with a high transverse
momentum trigger particle are reported for pp, d+Au, and Au+Au collisions at
200 GeV by the STAR experiment. Dijet structures are observed in pp, d+Au and
peripheral Au+Au collisions. An additional structure is observed in central
Au+Au data, signaling conical emission of correlated charged hadrons. The
conical emission angle is found to be 1.37 +- 0.02(stat) +0.06-0.07(syst),
independent of pt.Comment: 7 pages, 4 figures, 1 tabl
Observation of Two-source Interference in the Photoproduction Reaction
In ultra-peripheral relativistic heavy-ion collisions, a photon from the
electromagnetic field of one nucleus can fluctuate to a quark-antiquark pair
and scatter from the other nucleus, emerging as a . The
production occurs in two well-separated (median impact parameters of 20 and 40
fermi for the cases considered here) nuclei, so the system forms a 2-source
interferometer. At low transverse momenta, the two amplitudes interfere
destructively, suppressing production. Since the decay before
the production amplitudes from the two sources can overlap, the two-pion system
can only be described with an entangled non-local wave function, and is thus an
example of the Einstein-Podolsky-Rosen paradox. We observe this suppression in
200 GeV per nucleon-pair gold-gold collisions. The interference is (syst.) of the expected level. This translates into a
limit on decoherence due to wave function collapse or other factors, of 23% at
the 90% confidence level.Comment: Slightly revised version, to appear in PRL. 6 pages with 4 figure
Hydrazine drastically promoted Fenton oxidation of bisphenol A catalysed by a Fe-III-Co Prussian blue analogue
Herein, for the first time it has been demonstrated that hydrazine (Hz) could significantly promote the bisphenol A (BPA) degradation in the Fenton reaction catalysed by Fe[Co(CN)(6)]center dot 2H(2)O Prussian blue analogue (Fe-III-Co PBA). Results indicate that the dramatic enhancement of BPA degradation could be partly attributed to the induced homogeneous Fenton reaction by the enhanced dissolution of Fe-III-Co PBA. Meanwhile, the Hz coordinated iron site (H2NH2N-Fe), which is evolved from the original water coordinated iron site (H2O-Fe), was identified as the main active site. A possible reaction pathway involving the proposed active iron species was proposed. (C) 2016 Elsevier B.V. All rights reserved
'Fragile Superconductivity': A Kinetic Glass Transition in the Vortex Matter of the High-temperature Superconductor YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>
Using high-resolution thermal expansion and magnetization measurements, we provide experimental evidence for a kinetic glass transition in the vortex matter of YBa2Cu3O7-δ with some disorder. This transition, which represents the true superconducting transition in a magnetic field, exhibits many of the features of the usual glass transition found in supercooled structural liquids such as window glass. We demonstrate, using both kinetic and thermodynamic criteria, that this vortex matter is the most fragile system known to date, which we argue makes it possible to investigate the behavior very close to the Kauzmann temperature. Vortex matter, we suggest, may be a model system to study glassy behavior in general, which is expected to lead to a better understanding of the strong-fragile behavior in structural glasses
Graphene encapsulated FexCoy nanocages derived from metal-organic frameworks as efficient activators for peroxymonosulfate
A series of nitrogen-doped graphene encapsulated FexCoy bimetallic (FexCoy@C) nanocages were newly fabricated via a one-step thermal decomposition of Prussian blue analogue FeyCo1-y[Co(CN)(6)](0.67)center dot nH(2)O nanospheres at different temperatures. The as-synthesized FexCoy@C nanocages were systematically characterized and applied as effective catalysts to activate peroxymonosulfate (PMS) for the removal of bisphenol A (BPA). The catalytic activity of Fe3Co7@C-650 obtained at 650 degrees C was found to be the highest and also much higher than that of metallic cobalt, cobalt oxide and cobalt-iron spinels. The nitrogen-doped graphene shells were demonstrated to be effective in preventing the release of metal ions, thus resulting in a better stability. Furthermore, the BPA degradation pathway was proposed based on GC-MS and LC-MS results. The involved radicals were identified through electron paramagnetic resonance and radical scavenger experiments. Based on the systematic characterization of the catalyst before and after the catalytic oxidation reaction, the overall mechanism of PMS activation over FexCoy@C nanocages was proposed. Results indicate that FexCoy@C nanocages are available to serve as promising materials for environmental remediation by activation of PMS