173 research outputs found
Orbital correlations in the pseudo-cubic \emph{O} and rhombohedral -phases of LaMnO
The local and intermediate structure of stoichiometric LaMnO has been
studied in the pseudocubic and rhombohedral phases at high temperatures (300 to
1150 K). Neutron powder diffraction data were collected and a combined Rietveld
and high real space resolution atomic pair distribution function analysis
carried out. The nature of the Jahn-Teller (JT) transition around 750 K is
confirmed to be orbital order to disorder. In the high temperature orthorhombic
() and rhombohedral () phases the MnO octahedra are still fully
distorted locally. The data suggest the presence of local orbitally ordered
clusters of diameter \AA (four MnO octahedra) implying
strong nearest neighbor JT anti-ferrodistortive coupling.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Le
Local Structure of La1-xSrxCoO3 determined from EXAFS and neutron PDF studies
The combined local structure techniques, extended x-ray absorption fine
structure (EXAFS) and neutron pair distribution function analysis, have been
used for temperatures 4 <= T <= 330 K to rule out a large Jahn-Teller (JT)
distortion of the Co-O bond in La1-xSrxCoO3 for a significant fraction of Co
sites (x <= 0.35), indicating few, if any, JT-active, singly occupied e_g Co
sites exist.Comment: 5 page
Direct observation of the formation of polar nanoregions in Pb(MgNb)O using neutron pair distribution function analysis
Using neutron pair distribution function (PDF) analysis over the temperature
range from 1000 K to 15 K, we demonstrate the existence of local polarization
and the formation of medium-range, polar nanoregions (PNRs) with local
rhombohedral order in a prototypical relaxor ferroelectric
Pb(MgNb)O. We estimate the volume fraction of the PNRs as a
function of temperature and show that this fraction steadily increases from 0 %
to a maximum of 30% as the temperature decreases from 650 K to 15 K.
Below T200 K the PNRs start to overlap as their volume fraction reaches
the percolation threshold. We propose that percolating PNRs and their
concomitant overlap play a significant role in the relaxor behavior of
Pb(MgNb)O.Comment: 4 pages, 3 figure
Positional disorder of Ba in the thermoelectric germanium clathrate Ba6Ge25
The local structure of Ba6Ge25 has been studied by x-ray diffraction and the
atomic pair distribution function technique at 40 K and room temperature.
Unambiguous evidence has been found that two out of three types of Ba atoms in
Ba6Ge25 move off their positions and become locked in split sites at low
temperatures.Comment: 5 pages and 4 figures, submitted to Solid State Communication
Nova edició del workshop sobre "Mètodes Ràpids i Automatització en Microbiologia Alimentària" - memorial DYCFung
El XIX workshop sobre Mètodes Ràpids i Automatització en Microbiologia Alimentària (MRAMA) - memorial DYCFung, va ser organitzat en línia des de la Facultat de Veterinària de la UAB el mes de novembre passat. Celebrat anualment, amb un contingut aplicat i de futur, el MRAMA amplia i difon els coneixements teòrics i pràctics sobre mètodes innovadors per a detectar, comptar, aïllar i caracteritzar ràpidament els microorganismes, i els seus metabòlits, habituals en els aliments i l'aigua.El XIX workshop sobre Métodos Rápidos y Automatización en Microbiología Alimentaria (MRAMA) - memorial DYCFung, fue organizado en línea desde la Facultad de Veterinaria de la UAB el pasado mes de noviembre. Celebrado anualmente, con un contenido aplicado y de futuro, el MRAMA amplía y difunde los conocimientos teóricos y prácticos sobre métodos innovadores para detectar, contar, aislar y caracterizar rápidamente los microorganismos, y sus metabolitos, habituales en los alimentos y el agua
Local structural studies of BaKFeAs using atomic pair distribution function analysis
Systematic local structural studies of BaKFeAs system are
undertaken at room temperature using atomic pair distribution function (PDF)
analysis. The local structure of the BaKFeAs is found to be
well described by the long-range structure extracted from the diffraction
experiments, but with anisotropic atomic vibrations of the constituent atoms
( = ). The crystal unit cell parameters, the
FeAs tetrahedral angle and the pnictogen height above the Fe-plane are seen
to show systematic evolution with K doping, underlining the importance of the
structural changes, in addition to the charge doping, in determining the
properties of BaKFeAs
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