1. National Synchrotron Light Source Seminar

    "Characterization of the fluctuating charge states in transition meta oxides using local structure as a probel"

    A.M. Milinda Abeykoon

    Thursday, June 13, 2013, 1 pm
    Seminar Room, Bldg. 725

    Hosted by: Eric Dooryhee

    It is becoming apparent that nanoscale fluctuations in the charge state are important to the physics of transition metal oxides. The temperature evolution of structural modulation associated with charge (co) and spin order (so) in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction [1]. For the first time, we report an anomalous shrinking of the "a" lattice parameter that correlates with Tco, at the temperature where long-range stacking order of charge stripes disappears. In addition, we report anomalies in the mperature evolution of the refined atomic displacement parameters (ADP) and local structural parameters in the atomic pair distribution function (PDF), which show quite different temperature dependence consistent with the persistence of localized charges, presumably in the form of short range ordered dynamic charge stripe domains, over a broad temperature range above Tco. Similar effects are seen in LiRh2O4 where, at low temperature, the charges localize to form spin and structural dimers, which may be ordered or disordered [2]. Detailed temperature dependent xPDF measurements carried out at the recently constructed beamline, X17A-NSLS yield remarkable amount of information about the local dimer state of LiRh2O4. These were the first scientific data collected at X17A. Finally, I will present our recent demonstration that one can obtain quantitative PDFs from nanoparticles using a laboratory transmission electron microscope (TEM) [3]. This is a very exiting development for characterization of nanoparticles. Currently, we are developing this technique further to study thin films of transition metal oxides and other strongly correlated materials.