Computational studies of solid state materials for practical applications

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The Ni-rich Ni55Ti45 composition of the NiTi alloy is a promising material for aerospace bearing materials. Spiral orbit tribometry friction tests performed on Ni-rich Ni55Ti45 titanium ball bearings indicate that this alloy is a promising candidate for future aerospace bearing applications. Microstructural characterization of the bearing specimens was performed using transmission electron microscopy and energy dispersive spectroscopy, with NiTi, Ni4Ti3, Ni3Ti, and Ni2Ti4Ox phases identified within the microstructure of the alloy. Density functional theory (DFT) was applied to predict the electronic structure of the NixTiy phases, including the band structure and site projected density of states. Ultraviolet photoemission spectroscopy was used to verify the density of states results from the density functional theory calculations, with good agreement observed between experiment and theory. Plane wave ab initio DFT calculations of the B2 NiTi (100), (110), and (111) surfaces, the B2 and B19´ phases of NiTi, and the supercell structures of NiTi, Ni4Ti3 and Ni3Ti are also reported. Electronic energies from the electronic structure calculations are used to assess relative stability of the different surface and supercell geometries. DFT was applied using a plane wave approach for solids to determine the band gap energies in a series of Pb3C6X6 semiconducting extended-network organic structures, to determine the phase stability in the NiTi alloy system, and to study the surface of the (bcc) B2 phase of NiTi. To reveal the molecular structure and optoelectronic properties of these materials, a detailed ab-initio theoretical investigation of the solid-state properties was performed. Density functional theory was applied to predict the electronic structure of the NixTiy phases, including the band structure and site projected density of states. Organo-metallic compounds are also an important class of materials for organic electronic devices due to their semiconducting properties. Ground state geometries, band structure, density of states, and charge density were calculated using density functional theory using the PBE exchange-correlation functional as well as the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. The results show that the optical properties and band gap energies can be easily tuned by chemical modifications of the substituent X atom in Pb3(C6X6). Calculations of substituent atoms S, O, Se, and Te are presented. TiV-based alloys are promising candidates for NiMH batteries, as it is well established that the V-based (bcc) solid solution phase acts as the major hydrogen absorbing phase wguke the (hcp) Ti phase acts mainly as a catalyst for electrochemical hydrogenation and dehydrogenation. To achieve improved electrochemical performance a precise knowledge of the microstructure is required. Therefore, the influence of the interfacial energy on the material phase stability was investigated for a series of TiV multi-laminate thin films. Experiments revealed that at a higher layer thickness, the α (hcp) phase is the most stable. As the layer thickness is reduced, a transformation from the α (hcp) phase to the ß (bcc) phase occurs. Atomic-scale characterization of the transformed specimen by atom probe tomography reveals V interfacial diffusion between the layers. Equivalent crystal theory based calculations confirm the V interfacial diffusion mechanism. The predicted segregation profiles match those obtained experimentally.

Electronic Thesis or Dissertation
Chemistry, Engineering