Kinetic Monte Carlo model of charge transport in hematite ({alpha}-Fe{sub 2}O{sub 3})

Journal Article · Fri Sep 28 00:00:00 EDT 2007 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2768522· OSTI ID:21024220

Kerisit, Sebastien; Rosso, Kevin M ^[1]

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1. Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354 (United States)

The mobility of electrons injected into iron oxide minerals via abiotic and biotic electron transfer processes is one of the key factors that control the reductive dissolution of such minerals. Building upon our previous work on the computational modeling of elementary electron transfer reactions in iron oxide minerals using ab initio electronic structure calculations and parametrized molecular dynamics simulations, we have developed and implemented a kinetic Monte Carlo model of charge transport in hematite that integrates previous findings. The model aims to simulate the interplay between electron transfer processes for extended periods of time in lattices of increasing complexity. The electron transfer reactions considered here involve the II/III valence interchange between nearest-neighbor iron atoms via a small polaron hopping mechanism. The temperature dependence and anisotropic behavior of the electrical conductivity as predicted by our model are in good agreement with experimental data on hematite single crystals. In addition, we characterize the effect of electron polaron concentration and that of a range of defects on the electron mobility. Interaction potentials between electron polarons and fixed defects (iron substitution by divalent, tetravalent, and isovalent ions and iron and oxygen vacancies) are determined from atomistic simulations, based on the same model used to derive the electron transfer parameters, and show little deviation from the Coulombic interaction energy. Integration of the interaction potentials in the kinetic Monte Carlo simulations allows the electron polaron diffusion coefficient and density and residence time around defect sites to be determined as a function of polaron concentration in the presence of repulsive and attractive defects. The decrease in diffusion coefficient with polaron concentration follows a logarithmic function up to the highest concentration considered, i.e., {approx}2% of iron(III) sites, whereas the presence of repulsive defects has a linear effect on the electron polaron diffusion. Attractive defects are found to significantly affect electron polaron diffusion at low polaron to defect ratios due to trapping on nanosecond to microsecond time scales. This work indicates that electrons can diffuse away from the initial site of interfacial electron transfer at a rate that is consistent with measured electrical conductivities, but that the presence of certain kinds of defects will severely limit the mobility of donated electrons.

• OSTI ID: 21024220
• Journal Information: Journal of Chemical Physics, Vol. 127, Issue 12; Other Information: DOI: 10.1063/1.2768522; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANISOTROPY
CHARGE TRANSPORT
COMPUTERIZED SIMULATION
DIFFUSION
DISSOLUTION
ELECTRIC CONDUCTIVITY
ELECTRON MOBILITY
ELECTRON TRANSFER
ELECTRONIC STRUCTURE
ELECTRONS
HEMATITE
IRON OXIDES
MOLECULAR DYNAMICS METHOD
MONOCRYSTALS
MONTE CARLO METHOD
TEMPERATURE DEPENDENCE
VACANCIES