The effects of atmospheric CO 2 on surface segregation and phase formation in La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF-6428) were investigated. (001)-oriented LSCF-6428 thin films were deposited on lattice matched (110)-oriented NdGaO 3 (NGO) substrates by Pulsed Laser Deposition (PLD). Using the synchrotron technique of Total Reflection X-ray Fluorescence (TXRF), it was found that the kinetics of Sr surface segregation was enhanced when annealing at 800°C in a high CO 2 partial pressure, as compared to a similar anneal in a CO 2-free atmosphere, with the oxygen partial pressure being constant in both cases. HArd X-ray PhotoElectron Spectroscopy (HAXPES) measurements showed that the contribution of the surface carbonate to surface oxide phases increased significantly for the sample annealed in the high-CO 2 atmosphere. Atomic Force Microscopy (AFM) studies showed enhanced surface phase formation during the high-CO 2 partial pressure anneal. Density functional theory (DFT) calculations provide a thermodynamic basis for the enhanced kinetics of surface segregation in the presence of atmospheric CO 2 .

We present a systematic synchrotron radiation photoemission spectroscopy study of the interaction of O 2 with defective La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ (100) surfaces at low temperatures.First, the surface chemical evolution during low energy Ar + ion sputtering is investigated and is found to create oxygen vacancies. Subsequently, the interaction of the O 2 molecules with La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ (100) surface is observed to create an insulating phase. We performed a detailed core-level peak-fitting analysis to identify the chemical nature of this phase and to probe the role of vacancies in the formation of this phase.

The luminescence of ZnGa2O4 and ZnGa2O4 doped with divalent manganese was studied by performing excitation, emission, and decay time measurements in the temperature range from 4.2 to 500 K. From the results of these measurements the following mechanism can be proposed. Excitation into the gallate host lattice leads to the formation of electron-hole pairs which recombine radiatively on either the gallate groups or Mn2 or nonradiatively on quenching centers, depending on the temperature. In the first case a blue emission is observed, whereas the maximum of the green Mn2 emission is at about ,500 nm. At 4.2 K the effective distance of energy transport from excited gallate to emitting Mn2 is estimated to be 40 A. Due to the increasing mobility of the exciton this value increases at higher temperatures. Furthermore, the luminescence properties are found to be dependent on the preparation conditions. InfroductionThe luminescence of divalent manganese has been studied intensively. Although other valencies of this ion, as e.g., Mn4 Mn5, and Mn6, also show interesting luminescent features, the properties of Mn2 are most widely studied and used in many luminescent materials.4 Mn2 has the 3d5 configuration and from the Tanabe-Sugano diagram, it follows that in octahedral coordination the ground level is 'A,. Emission arises from the 4T, (4G) level, the energy of which depends strongly on the crystal field strength. The optical absorption transitions are parity and spin forbidden.There is growing interest in ZnGa2O4 and Mn2-activated ZnGa2O4 as low-voltage cathodoluminescence phosphors for application in vacuum fluorescent and field emission displays.5 ZnGa2O4 has the spinel structure.6'7 Spinels are compounds with formula AB204 with eight formula units in the unit cell; the space group is Fd3m (Ok).

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Formation of oxygen vacancies by introducing various mixed-valent cation dopants is a common practice to improve the cathode performance in solid oxide fuel cells. A computational procedure is developed in this work to predict the equilibrium oxygen vacancy non-stoichiometric concentrations at experimentally relevant temperatures and oxygen partial pressures for both bulk and surface oxide phases. The calculations are based on the first-principles density functional theory and a constrained free-energy functional. Quantitative agreements are found by direct comparisons to the thermogravimetry and solid electrolyte coulometry measurements for the strontium-doped lanthanum cobalt iron oxides at different compositions. Our results indicate that the oxygen vacancies are energetically stabilized at surfaces for all temperatures and all oxygen partial pressures, while such surface stabilization effects become stronger at higher temperatures and lower oxygen partial pressures.