Lead(II) tetrafluorostannate(II) (PbSnF4) exhibits the highest conductivity among the reported fluoride ion conductors. The previous studies analyzed the diffusion mechanism of fluoride ion based on the crystal
structure with the diffraction studies and the nuclear magnetic resonance measurements. In this study, the
electronic structure of PbSnF4 is investigated using fluorine K-edge X-ray absorption spectroscopy. The composition of Pb causes the electronic structure change of the vacant F-2p orbital which is the hybridized Pb-6s and Sn-5s orbitals. The electronic structure change is related to the tendency of the fluoride ion conductivity in Pb1-xSnxF4.
The cerium species have been characterized during the temperature-programmed reduction (TPR) process under H2 atmosphere by means of the X-ray absorption fine structure (XAFS) spectroscopy and the X-ray diffraction (XRD) method. The in-situ XAFS measurements revealed that the CeO2 species was finally reduced to Ce2O3 at 900 ºC with an intermediate state generated in the temperature rage of 550–750 ºC. The absorption edge shift of the X-ray absorption near edge structure (XANES) spectra indicated that the non-stoichiometric compound was formed as the intermediate species, and the estimated composition was CeO1.65. The in-situ XRD measurements during the TPR process showed the shift of the diffraction lines of CeO2 above 400 ºC, indicating the formation of the non-stoichiometric intermediate. The quantitative analysis of the lattice parameter demonstrated that the crystal plane spacing for the (111) plane of the non-stoichiometric intermediate was expanded by about 0.03 Å than the initial CeO2 phase.
The preparation process of metallic Ni(0) particles supported on LiFePO4 was analyzed using the in-situ XAFS technique in order to produce the carbon nanotube on LiFePO4 by methane decomposition reaction catalyzed by metallic Ni(0) for its utilization as an active material of a lithium ion battery. The Ni species was supported on LiFePO4 by the impregnation method. The LiFePO4 was oxidized to FePO4 during the calcination process. The in-situ XAFS analysis for the reduction process revealed that LiFePO4 was regenerated at the temperature range between 380 °C and 490 °C. In this reduction process, the supported Ni species was changed from NiO to metallic Ni(0). This study achieved to find out the appropriate preparation conditions of the metallic Ni(0) particle on LiFePO4.
The growth mode of Cu nanoparticles deposited on the rutile TiO2(110) surfaces have been investigated by high-resolution medium energy ion scattering (MEIS). The observed MEIS spectra were well reproduced assuming the hemispherical and two-dimensional islands. The MEIS results indicate that the two-dimensional islands of Cu nanoparticles grow initially up to Cu coverage of 0.5 ML and then three -dimensional islands growth become dominant. Interestingly, the growth mode is almost the same for both reduced TiO2 and oxygenrich TiO2. These results indicate that Cu nanoparticles are formed as both two- and three-dimensional islands on reduced and oxygen-rich TiO2.
Diffusion phenomena of lithium ion in silicon negative electrode of lithium-ion battery are one of the fundamental properties, which have not been fully understood at this moment. In this study, using silicon single crystal electrodes, the diffusion behavior was investigated. Electrochemical method and Si K-edge X-ray absorption spectroscopy were applied to estimate the state of alloying in silicon-lithium system. The results of cyclic voltammetry measurements show larger reduction and oxidation current density in Si (100) than Si (111), indicating preferential diffusion into Si (100). X-ray absorption near edge structure (XANES) at Si K-edge depends on the state of alloying, which can be used for the estimation of alloying state. The apparent diffusion coefficient of lithium ion in single crystal electrodes of (100) calculated from the analysis of XANES is higher than that of (111).