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Published May 10, 2016 | Supplemental Material
Journal Article Open

Polaron Mobility and Disordering of the Sodium Sublattice in Triphylite-Na_xFePO_4

Abstract

The interplay between sodium ordering and electron mobility in Na_xFePO_4 was investigated using a combination of synchrotron X-ray diffraction and Mössbauer spectrometry. Synchrotron X-ray diffraction measurements were carried out for a range of temperatures between 298 and 553 K. Rietveld analysis of the diffraction patterns was used to determine the temperature of sodium redistribution on the lattice. This diffraction analysis also gives new information about the phase stability of the system. Mössbauer spectra were collected in the same temperature range. An analysis of the temperature evolution of the spectral shapes was used to identify the onset of fast electron hopping and determine the polaron hopping rate. The temperature evolution of the iron site occupancies from the Mössbauer measurements, combined with the synchrotron diffraction results, shows a relationship between the onset of fast electron dynamics and the loss of local order on the sodium sublattice.

Additional Information

© 2016 American Chemical Society. Received: January 19, 2016; Revised: April 14, 2016; Publication Date (Web): April 15, 2016. This work was supported as part of EFree, an Energy Frontier Research Center, under Award No. DE-SG0001057. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOE-BES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The authors declare no competing financial interest.

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