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Oxygen Vacancy Concentration (oxygen + vacancy_concentration)
Selected AbstractsNeutron powder diffraction study of the anion-deficient La0.70Sr0.30MnO3.00-, manganitesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009S. V. Trukhanov Abstract Using powder neutron diffraction method the magnetic structure of the anion-deficient La0.70Sr0.30MnO3.00-, (, = 0, 0.15; 0.20) solid solutions at different temperatures has been defined. It is established that the magnetic structure changes with oxygen vacancies concentration. For the investigated samples the structural phase transitions have not been detected. The obtained data confirm the conception of the magnetic phase state forming for the Sr-doped anion-deficient manganites. In according to this conception in case of orbital ordering absence the lowering of the coordination of the magnetic ion results to change of the indirect superexchange interactions Mn3+ -O-Mn3+ sign from positive to negative. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flame-Synthesized Ceria-Supported Copper Dimers for Preferential Oxidation of COADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Richard Kydd Abstract Rapid synthesis of CuCeO2 catalysts by flame spray pyrolysis produces highly active Cu dimer morphologies without the need for additional catalyst pretreatment. The active Cu component is enriched onto the CeO2 surface at concentrations higher than the nominal loading with no evidence of amorphous or crystalline CuO phase. Increasing the Cu content results in a morphological transition from isolated Cu monomers to oxygen-bridged dimers and an associated increase in oxygen vacancy concentration. Dimer-containing CuCeO2 catalysts display high levels of activity and selectivity in the low-temperature preferential oxidation of CO. Experimental measurements and simulations suggest that the geometry of the dimer presents a comparatively ionic CuO bond at the catalyst surface. Further studies indicate that these ionic dimer species promote preferential CO oxidation at lower temperatures than observed for monomeric Cu species. This is the first report to explicitly propose and demonstrate that the structural distortion associated with the formation of Cu dimers directly induces increased bond ionicity at the catalyst surface and that these changes are responsible for improved catalytic activity. [source] Oxygen Diffusion in Yttria-Stabilized Zirconia: A New Simulation ModelJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004R. Krishnamurthy We present a multiscale modeling approach to study oxygen diffusion in cubic yttria-stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long-time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation-dopant-induced correlation effects in support of the above explanation. [source] Laser-induced oxygen vacancy formation and diffusion on TiO2 (110) surfaces probed by photoemission electron microscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2006Gang Xiong Abstract Photoemission electron microscopy is used to probe photon-induced oxygen vacancies generated on TiO2 (110)-(1×2) surfaces. An increased oxygen vacancy concentration within the irradiated region leads to an increase of local photoelectron emission. The local oxygen deficient region can be compensated by exposing the surface to molecular oxygen at 1×10,5 Torr, or via surface diffusion at 450 K in vacuum. The surface diffusion coefficient is estimated to be on the order of 10,12 m2/s. Photoemission electron microscopy allows in situ studies of surface electronic defect formation and removal. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||