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Article

Phonons and Thermodynamics of Unmixed and Disordered Li_0.6FePO₄

R. Stevens,*^† J. L. Dodd,^‡ M. G. Kresch,^† R. Yazami,^‡ and B. Fultz^‡

Division of Engineering and Applied Science, and The CNRS CALTECH International Laboratory on Materials for Electrochemical Energetics, California Institute of Technology, Pasadena, California 91125

B. Ellis and L. F. Nazar

Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1

J. Phys. Chem. B, 2006, 110 (45), pp 22732–22735

DOI: 10.1021/jp063831l

Publication Date (Web): October 13, 2006

Corresponding author. E-mail: rstevens@caltech.edu.

†

Division of Engineering and Applied Science, California Institute of Technology.

‡

The CNRS CALTECH International Laboratory on Materials for Electrochemical Energetics, California Institute of Technology.

Abstract

The lithium-storage material Li_0.6FePO₄ was studied by inelastic neutron scattering and differential scanning calorimetry. Li_0.6FePO₄ undergoes a transformation from a two-phase mixture (heterosite and triphylite) to a disordered solid-solution at 200 °C. Phonon densities of states (DOS) obtained from the inelastic neutron scattering were similar for the two-phase sample measured at 180 °C and the disordered sample measured at 220 °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.

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Published In Issue November 16, 2006
Received June 20, 2006
Revised September 7, 2006

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Article

Phonons and Thermodynamics of Unmixed and Disordered Li_0.6FePO₄