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Mineralogy, Mössbauer spectra and electrical conductivity of triphylite Li(Fe2+,Mn2+)PO4

Fehr, Karl-Thomas, Rupert Hochleitner, Elmar Schmidbauer, and Julius Schneider (2007), Mineralogy, Mössbauer spectra and electrical conductivity of triphylite Li(Fe2+,Mn2+)PO4, Phys. Chem. Minerals, 34, 485-494, doi:10.1007/s00269-007-0164-8.

The electrical conductivity of monocrystalline triphylite, Li(Fe2+,Mn2+)PO4, with the orthorhombic olivine-type structure was measured parallel (∥) to the [010] direction and ∥ [001] (space group Pnma), between ∼400 and ∼700 K. Electrical measurements on triphylite are of technological interest because LiFePO4 is a promising electrode material for rechargeable Li batteries. Triphylite was examined by electron microprobe, ICP atomic emission spectroscopy, X-ray diffraction, Mössbauer spectroscopy and microscopic analysis. The DC conductivity σDC was determined from AC impedance data (20 Hz–1 MHz) extrapolating to zero frequency. Triphylite shows σDC with activated behavior measured ∥ [010] between ∼500 and ∼700 K during the first heating up, with activation energy of E A = 1.52 eV; on cooling E A = 0.61 eV was found down to ∼400 K and extrapolated σDC (295 K) ∼10−9 Ω−1cm−1; ∥ [001] E A = 0.65 eV and extrapolated σDC(295 K) ∼10−9 to 10−10 Ω−1cm−1, measured during the second heating cycle. The enhanced AC conductivity relative to σDC at lower temperatures indicates a hopping-type charge transport between localized levels. Conduction during the first heating up is ascribed to ionic Li+ hopping. DC polarization experiments showed conduction after the first heating up to be electronic related to lowered activation energy. Electronic conduction appears to be coupled with the presence of Li+ vacancies and Fe3+, formed by triphylite alteration. For comparison, σDC was measured on the synthetic compound LiMgPO4 with olivine-type structure, where also an activated behavior of σDC with E A ∼1.45 eV was observed during heating and cooling due to ionic Li+ conduction; here no oxidation can occur associated with formation of trivalent cations.
Further information
  author = {Karl-Thomas Fehr and Rupert Hochleitner and Elmar Schmidbauer and Julius Schneider},
  journal = {Phys. Chem. Minerals},
  pages = {485-494},
  title = {{Mineralogy, M{\"o}ssbauer spectra and electrical conductivity of  triphylite Li(Fe2+,Mn2+)PO4}},
  volume = {34},
  year = {2007},
  url = {http://www.springerlink.com/content/q7u8934446043125/fulltext.pdf},
  doi = {10.1007/s00269-007-0164-8},
%0 Journal Article
%A Fehr, Karl-Thomas
%A Hochleitner, Rupert
%A Schmidbauer, Elmar
%A Schneider, Julius
%D 2007
%V 34
%J Phys. Chem. Minerals
%P 485-494
%T Mineralogy, Mössbauer spectra and electrical conductivity of  triphylite Li(Fe2+,Mn2+)PO4
%U http://www.springerlink.com/content/q7u8934446043125/fulltext.pdf
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