1,025 research outputs found
High-pressure synthesis of rock salt LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions
Metastable LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions with rock salt
crystal structure have been synthesized by solid state reaction of ZnO with
LiMeO2 complex oxides at 7.7 GPa and 1350-1450 K. Structure, phase composition,
thermal stability and thermal expansion of the recovered samples have been
studied by X-ray diffraction with synchrotron radiation. At ambient pressure
rock salt LiMeO2-ZnO solid solutions are kinetically stable up to 670-800 K
depending on the composition.Comment: 11 pages, 3 figures, 1 tabl
The Cross-Cultural Invariance of the Servant Leadership Survey: A Comparative Study across Eight Countries
This paper tests and confirms the cross-cultural equivalence of the Servant Leadership Survey (SLS) in eight countries and languages: The Netherlands, Portugal, Germany, Iceland, Italy, Spain, Turkey and Finland. A composite sample consisting of 5201 respondents from eight countries that all filled out the SLS was used. A three-step approach was adopted to test configural invariance, measurement equivalence, and structural equivalence. For the full 30-item version of the SLS, configural invariance and partial measurement equivalence were confirmed. Implications of these results for the use of the SLS within cross-cultural studies are discussed
Assessing Significance in High-Throughput Experiments by Sequential Goodness of Fit and q-Value Estimation
We developed a new multiple hypothesis testing adjustment called SGoF+ implemented as a sequential goodness of fit metatest which is a modification of a previous algorithm, SGoF, taking advantage of the information of the distribution of p-values in order to fix the rejection region. The new method uses a discriminant rule based on the maximum distance between the uniform distribution of p-values and the observed one, to set the null for a binomial test. This new approach shows a better power/pFDR ratio than SGoF. In fact SGoF+ automatically sets the threshold leading to the maximum power and the minimum false non-discovery rate inside the SGoF' family of algorithms. Additionally, we suggest combining the information provided by SGoF+ with the estimate of the FDR that has been committed when rejecting a given set of nulls. We study different positive false discovery rate, pFDR, estimation methods to combine q-value estimates jointly with the information provided by the SGoF+ method. Simulations suggest that the combination of SGoF+ metatest with the q-value information is an interesting strategy to deal with multiple testing issues. These techniques are provided in the latest version of the SGoF+ software freely available at http://webs.uvigo.es/acraaj/SGoF.htm
Structure of MnO nanoparticles embedded into channel-type matrices
X-ray diffraction experiments were performed on MnO confined in mesoporous
silica SBA-15 and MCM-41 matrices with different channel diameters. The
measured patterns were analyzed by profile analysis and compared to numerical
simulations of the diffraction from confined nanoparticles. From the lineshape
and the specific shift of the diffraction reflections it was shown that the
embedded objects form ribbon-like structures in the SBA-15 matrices with
channels diameters of 47-87 {\AA}, and nanowire-like structures in the MCM-41
matrices with channels diameters of 24-35 {\AA}. In the latter case the
confined nanoparticles appear to be narrower than the channel diameters. The
physical reasons for the two different shapes of the confined nanoparticles are
discussed.Comment: 8 pages, including 9 postscript figures, uses revtex4.cl
Effect of lattice volume and strain on the conductivity of BaCeY-oxide ceramic proton conductors
In-situ electrochemical impedance spectroscopy was used to study the effect
of lattice volume and strain on the proton conductivity of the yttrium-doped
barium cerate proton conductor by applying the hydrostatic pressure up to 1.25
GPa. An increase from 0.62 eV to 0.73 eV in the activation energy of the bulk
conductivity was found with increasing pressure during a unit cell volume
change of 0.7%, confirming a previously suggested correlation between lattice
volume and proton diffusivity in the crystal lattice. One strategy worth trying
in the future development of the ceramic proton conductors could be to expand
the lattice and potentially lower the activation energy under tensile strain
High-Temperature Transport Properties of Yb4−xSmxSb3
Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K
Structural and physical properties of layered oxy-arsenides LnRuAsO (Ln = La, Nd, Sm, Gd)
Polycrystalline samples of LaRuAsO, NdRuAsO, SmRuAsO, and GdRuAsO have been
synthesized and studied using powder x-ray diffraction, electrical transport,
magnetization, and heat capacity measurements. Variations in structural
properties across the series reveal a trend toward more ideal tetrahedral
coordination around Ru as the size of the rare earth element is reduced. The
lattice parameters of these Ru compounds show a more anisotropic response to
variation in Ln than their Fe analogues, and significant anisotropy in thermal
expansion is also observed. Transport measurements show metallic behavior, and
carrier concentrations near 10^21 - 10^22 electrons per cm^3 are inferred from
simple analysis of Hall effect measurements. Anomalies in resistivity,
magnetization, and heat capacity indicate antiferromagnetic ordering of rare
earth moments at 5 K for GdRuAsO, 4.5 K for SmRuAsO, and <2 K for NdRuAsO.
Magnetization measurements on LaRuAsO show no evidence of a magnetic moment on
Ru. Observed behaviors are compared to those reported for similar Fe and Ru
compounds
Evidence for Jahn-Teller distortions at the antiferromagnetic transition in LaTiO
LaTiO is known as Mott-insulator which orders antiferromagnetically at
K. We report on results of thermal expansion and temperature
dependent x-ray diffraction together with measurements of the heat capacity,
electrical transport measurements, and optical spectroscopy in untwinned single
crystals. At significant structural changes appear, which are
volume conserving. Concomitant anomalies are also observed in the
dc-resistivity, in bulk modulus, and optical reflectivity spectra. We interpret
these experimental observations as evidence of orbital order.Comment: 4 pages, 4 figures; published in Phys. Rev. Lett. 91, 066403 (2003
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