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Phonons and thermodynamics of unmixed and disordered Li0.6FePO4.

Stevens R, Dodd JL, Kresch MG, Yazami R, Fultz B, Ellis B, Nazar LF

Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA. rstevens@caltech.edu

The lithium-storage material Li(0.6)FePO(4) was studied by inelastic neutron scattering and differential scanning calorimetry. Li(0.6)FePO(4) undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 degrees C. Phonon densities of states (DOS) obtained from the inelastic neutron scattering were similar for the two-phase sample measured at 180 degrees C and the disordered sample measured at 220 degrees C. The vibrational entropy of transformation is 1.8 +/-0.9 J/(K mol), which is smaller than the configurational entropy difference of approximately 3.1 J/(K mol). The measured enthalpy of the disordering transition was estimated as 2.5 kJ/mol. The phonon data show a small change in lattice dynamics upon disordering.

Published 9 November 2006 in J Phys Chem B Condens Matter Mater Surf Interfaces Biophys, 110(45): 22732-5.
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