Regensburg 2010 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 35: New Materials: Optoelectronic and Photovoltaic Applications
HL 35.5: Vortrag
Mittwoch, 24. März 2010, 10:30–10:45, H13
Valence and core excitations in Li(1−x)FePO4 — •Michael Kinyanjui1,2, Peter Axmann2, Margret Wohlfahrt-Mehrens2, Philippe Moreau3, Florent Boucher3, and Ute Kaiser1 — 1University of Ulm, Albert Einstein Allee 11, 89081 Ulm, Germany — 2Centre for Solar Energy and Hydrogen Research, Helmholtzstr. 8, 89081 Ulm, Germany — 3Institut des Matériaux Jean Rouxel, UMR6502, CNRS - Université de Nantes, 2 rue de la Houssinière, B.P.32229, 44322 Nantes cedex, France
LiFePO4 is a potential cathode material for Li ion batteries applications. However, its electronic properties and the mechanism by which lithium ions are extracted or inserted into the lattice are still unclear. The electronic properties of LiFePO4 and FePO4 have been investigated using valence electron energy loss spectroscopy (VEELS), core-loss EELS and ab initio calculations. The VEELS spectra of FePO4 show interband transitions between 0-20 which are not observed in LiFePO4 VEELS spectra. Using the calculated imaginary part of the dielectric function, the interband transitions were assigned as rising from valence states with mainly O-2p character. The core-loss spectra in FePO4 show a pre-edge peak that is observed above the threshold of the main O-K edge. This is not observed in LiFePO4. The position of the pre-edge peak is determined by a charge transfer process which shifts the position of the Fe 3d bands with respect to the conduction band with the extraction of lithium ions from the LiFePO4 lattice. Therefore FePO4 can be considered to be a charge-transfer insulator while the LiFePO4 is a typical Mott-Hubbard insulator.