Structures, Structural Transfromations and Properties of Selected Elemental and Extended Solids
| dc.contributor.advisor | Yao, Yansun | |
| dc.contributor.committeeMember | Pywell, Rob | |
| dc.contributor.committeeMember | Couedel, Lenaic | |
| dc.contributor.committeeMember | Chen, Ning | |
| dc.contributor.committeeMember | Tse, John S | |
| dc.creator | Adeleke, Adebayo Abayomi | |
| dc.creator.orcid | 0000-0002-9057-431X | |
| dc.date.accessioned | 2021-05-31T13:58:32Z | |
| dc.date.available | 2021-05-31T13:58:32Z | |
| dc.date.created | 2021-05 | |
| dc.date.issued | 2021-05-31 | |
| dc.date.submitted | May 2021 | |
| dc.date.updated | 2021-05-31T13:58:33Z | |
| dc.description.abstract | The current boom in computer power has created avenue to study materials’ properties under extreme thermodynamic conditions where experimental characterization is very challenging. This thesis is an aggregation of several objectives ranging from the study of elemental as well as extended materials for technological, high energy density (HED), and geophysical applications; all at high pressure. The density functional theory (DFT), ab initio metadynamics and ab initio molecular dynamics (AIMD) methods have been employed to analyze structural phase transitions, electronic, vibrational, and mechanical properties of selected materials at high pressure. Where available, high-pressure-high-temperature (HPHT) experiments were combined with the various theoretical methods for complete elucidation of the system. The first set of projects in this thesis involve study of structural phase transition in two elements: carbon (C) and nitrogen (N). The first part presents the results of structural phase transition in a two-dimensional polymeric C60 after being subjected to uniaxial compression at high temperature in a metadynamics simulation. The new structure exhibits a mixed sp2/sp3 hybridization. The structure is stable at ambient condition and exhibits superior mechanical performance than most of widely used hard ceramics. The second part presents theoretical results on the identification, and characterization of single bonded nitrogen in crystal structure isostructural to black phosphorus (BP-N) at 146 GPa and 2200 K. The crystal structure exhibits a unique puckered two-dimensional layer exhibiting exciting physical and chemical phenomena including prospect for high energy density (HED) applications. Synchrotron x-ray diffraction and Raman spectroscopy were used for experimental characterization of the BP-N. First-principles methods were employed in the theoretical characterization. The second set of projects involve the theoretical studies of transition metal (TM) -TM alloys/compounds. The first part of the chapter investigates structural phase transition leading to shape memory loss in the shape memory alloy NiTi. The second part investigates the formation of Au-Fe compounds at high pressure. A detailed analysis of the transition kinetics and dynamical pathway in NiTi using the metadynamics method reveals the possibility of the B19′ phase of NiTi losing its shape memory when subjected to high stress conditions and heated above a critical temperature (Tc) of 700 K. Using the particle swarm-intelligence optimization algorithm interfaced with first principles methods, we predicted the formation of bulk intermetallic compounds of two bulk-immiscible components, Fe and Au. the systems are stabilized by pressure and notable electron transfer. Next, the results of theoretical studies of the formation of noble gas element - TM compound were presented. The identification of a thermodynamically stable compound of Argon (Ar) and nickel (Ni) under thermodynamic conditions representative of the Earth’s core using density functional calculations were presented. The study present evidence of the reactability of Ar with one of the Earth’s core’s main constituents, Ni. The compound of Ar and Ni was identified as ArNi with a L11 Laves structure. It was found that ArNi compound is stabilized by notable electron transfer from Ni to Ar. The final project is an extensive theoretical study of the formation of alkali metal-transition metal intermetallic compounds at high pressure and temperature relevant to the upper mantle and the core of the Earth. These studies were carried out using particle swarm-intelligence optimization and genetic algorithms interfaced with first principles methods. The first part investigates the formation of K-Fe compounds at thermodynamics conditions relevant to the Earth’s interior while the second part investigates the formation of K-Ni compounds in the Earth’s interior. It was found that K and Fe can form intermetallic compounds that are stabilized by high pressure and energy reordering of atomic orbital. Phase transitions were also reported and the instabilities that induce them were also investigated. Furthermore, the study on K-Ni systems identify the crystal structure for the long-sought structure of the only experimentally known K-Ni compound to date. The identified K2Ni exhibits a semiconducting ground state with an indirect bandgap. The results of both studies indicate that the chemical properties of elements can change dramatically under extreme conditions and could have significant implications for understanding the Earth’s interior. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | https://hdl.handle.net/10388/13401 | |
| dc.subject | Phase transition, Density Functional Theory, Structure prediction, Molecular Dynamics, Metadynamics, | |
| dc.title | Structures, Structural Transfromations and Properties of Selected Elemental and Extended Solids | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Physics and Engineering Physics | |
| thesis.degree.discipline | Physics | |
| thesis.degree.grantor | University of Saskatchewan | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |