Orbital correlations in the pseudo-cubic \emph{O} and rhombohedral R{R}-phases of LaMnO3_3

The local and intermediate structure of stoichiometric LaMnO$_3$ 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 ($O$) and rhombohedral ($R$) phases the MnO$_6$ octahedra are still fully distorted locally. The data suggest the presence of local orbitally ordered clusters of diameter $\sim 16$ \AA ($\sim$four MnO$_6$ 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(Mg1/3_{1/3}Nb2/3_{2/3})O3_3 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(Mg$_{1/3}$Nb$_{2/3}$)O$_3$. 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 $\sim$ 30% as the temperature decreases from 650 K to 15 K. Below T$\sim$200 K the PNRs start to overlap as their volume fraction reaches the percolation threshold. We propose that percolating PNRs and their concomitant overlap play a significant role in the relaxor behavior of Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$.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 Ba1−x_{1-x}Kx_xFe2_2As2_2 using atomic pair distribution function analysis

Systematic local structural studies of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ system are undertaken at room temperature using atomic pair distribution function (PDF) analysis. The local structure of the Ba$_{1-x}$K$_x$Fe$_2$As$_2$ 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 ($U_{11}$ = $U_{22} \ne U_{33}$). The crystal unit cell parameters, the FeAs$_4$ 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 Ba$_{1-x}$K$_x$Fe$_2$As$_2$