Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 161-171). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1945. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Bibliography: leaves 161-162.

Thesis (M.Sc. (Physics)) -- University of Limpopo, 2021 / The stead-fast demand for sustainable lithium-ion batteries (LIB) with competitive electrochemical properties, safety, reduced costs, and long-life cycle, calls for intensive efforts towards the development of new battery cathode materials. The layered transition metal oxides formulated LiMO2 (M: Mn, Ni and Co) have attracted considerable attention due to their capability to optimize the discharge capacity, cycling rate, electrochemical stability and lifetime. The transition metals Mn, Ni and Co (NMC) have been reported to contribute towards enhancement of the performance of NMC based lithium-ion batteries. In this work, the electronic properties of transition metal oxides LiMO2 (M: Mn, Ni and Co) as individual crystal structures are studied using density functional theory (DFT+U) in the local density and generalized gradient approximation (LDA and GGA). The Hubbard U values together with the low spin transition metal in 3+ charge state (Mn3+, Ni3+ and Co3+) predicts the electrical conductivity of the materials. The conductivity is associated predominantly with 3d states of the transition metals (Mn, Ni and Co) and 2d character in oxygen. The LiNiO2 material is high in conductivity, while both LiMnO2 and LiCoO2 are low in electrical conductivity. All independent elastic constants satisfy the mechanical stability criterion of orthorhombic materials implying stability of the materials. However, the phonon dispersion curves display imaginary vibration along high symmetry direction for LiCoO2. The heats of formations predict that the LiNiO2 is the most thermodynamically stable material while the LiMnO2 is the least thermodynamically stable material. The derived interatomic potentials produced NiO and CoO structures with a difference of less than 1% and 9% respectively, from the experimental structures. The structures were melted at temperatures close to their experimental values from molecular dynamics. The radial distribution curves and Nano architectures presented the melting point of NiO and CoO at 2250K and 2000K respectively. All independent elastic constants satisfy the mechanical stability criterion of cubic materials implying stability of the materials. The high electrical conductivity and thermodynamic favourability LiNiO2 suggests that the material can be the most recommendable material as a cathode material and further improved through doping. This will add the overall enhancement of the electrochemical performance while stabilizing structural stability of the cathode material in high energy density Li-ion batteries. / National Research Foundation (NRF)

Thesis (Ph.D. (Physics)) --University of Limpopo, 2013 / The intention of the current study is to investigate structure, ion transport and reactivity of various forms of the cobalt pentlandite, Co9S8, at different temperatures using atomistic simulation methods with the support of electronic structure calculations. The first interatomic potentials of Co9S8 were derived with input data as structure and elastic properties from experiment and electronic structure calculations respectively. The potentials were validated by running energy minimization and molecular dynamics calculations. Structure, elastic properties and phonon spectra were well reproduced, together with the complex high temperature transformations and melting of Co9S8 as deduced from crystal structure, radial distribution functions, density profiles and diffusion coefficients. Amongst the high symmetry surfaces {111}, {101} and {101} atomistic surface energy calculations proposed the {111} surface of Co9S8 as the most stable in agreement with experimental morphologies, and water adsorption energies on the such surfaces which mostly agreed with those from electronic structure calculations. The structural and ion transport variations with temperature were investigated and predicted surface melting at lower temperatures than the bulk. The effects of hydration on the surfaces at low and high temperatures were also studied. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. Generally for {111}, {101} nanoparticles, high temperature transitions were abrupt for smaller nanoparticles and these tended to disintegrate and form voids. However, for larger nanoparticles the transitions were more gradual. Transitions in the {100} bound nanoparticles were less dramatic for all sizes and the formation of voids was reduced at high temperatures. Generally, the melting temperatures of different sizes of nanoparticles increases with the particle size hence approach the bulk limit. The interaction of nanoparticles with water was investigated. / Anglo Platinum, National Research Foundation (South Africa), and The Royal Society (UK)