Electronic correlations in Lix̳ CoO₂
Name
55858334-MIT.pdf
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5.15 MB
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8e8565c8c58f08c5e76f49c98dcac993
Author(s)
Marianetti, Chris, 1975-
Advisor(s)
Gerbrand Ceder.
Date Issued
2004
Publisher
Massachusetts Institute of Technology
Abstract
The purpose of this thesis is further the understanding of the electronic properties of LixCoO2 using density functional theory (DFT) and the dynamical mean-field theory (DMFT). Three main problems are addressed. First, the influence of hybridization among the eg and oxygen orbitals is studied using DFT and a modified Hubbard model which is solved within DMFT. It has long been known that doping holes into the t2g bands are accompanied by a rehybridization which causes electron density to be added to the eg states and hole density to the oxygen states. This so-called rehybridization mechanism has been demonstrated to be a competition between the hybridization, which prefers to occupy the eg orbitals, and the Co on-site coulomb repulsion, which prefers to have the eg orbitals empty to avoid the strong coulomb interaction. It is also shown that eg-oxygen hybridization effectively screens the low energy t2g excitations, which has implications for the low energy Hamiltonian corresponding to hydrated Nal/3CoO2. Second, the hereto anomalous first-order metal-insulator transition in LixCoO2 (0.75 < x < 0.95) is identified as a Mott transition of impurity states. DFT supercell calculations indicate that for dilute Li vacancy concentrations (ie x > 0.95), the vacancy potential binds its hole and forms an impurity state which leads to a Mott insulator. We argue that the first-order transition is due to a decomposition of the impurity band, and is perhaps the only known example of a first-order Mott transition in a doped semiconductor. Third, LiCoO2 possesses a high energy photoemission satellite which hereto could not be predicted by any first-principles method. LDA+DMFT solved within multi-band iterated perturbation theory successfully predicts the satellite.
Description
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.
In title on t.p., double-underscored "x" appears as subscript.
Includes bibliographical references (p. 120-123).
Subjects
Materials Science and Engineering.
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
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