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Published September 12, 2014 | Published
Journal Article Open

Polaron-ion correlations in Li_xFePO_4 studied by x-ray nuclear resonant forward scattering at elevated pressure and temperature

Abstract

Valence fluctuations of Fe^(2+) and Fe^(3+) were studied in a solid solution of Li_xFePO_4 by nuclear resonant forward scattering of synchrotron x rays while the sample was heated in a diamond-anvil pressure cell. The spectra acquired at different temperatures and pressures were analyzed for the frequencies of valence changes using the Blume-Tjon model of a system with a fluctuating Hamiltonian. These frequencies were analyzed to obtain activation enthalpies and an activation volume for polaron hopping. There was a large suppression of hopping frequency with pressure, giving an activation volume for polaron hopping of 5.8±0.7 Å^ 3. This large, positive value is typical of ion diffusion, which indicates correlated motions of polarons and Li^+ ions that alter the dynamics of both. Monte Carlo simulations were used to estimate the strength of the polaron-ion interaction energy.

Additional Information

© 2014 American Physical Society. Received 31 December 2013; Revised manuscript received 6 June 2014; Published 12 September 2014. We thank C. W. Li for discussions. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by CIW, CDAC, UNLV, and LLNL through funding from DOE-NNSA, DOE-BES, and NSF. Use of the APS was supported by DOE-BES, under Contract No. DE-AC02-06CH11357. This work was supported as part of EFree, an Energy Frontier Research Center, under Award No. DE-SG0001057.

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Published - PhysRevB.90.094303.pdf

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August 20, 2023
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