ETD Collection

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Author: search.filters.author.Rugut, Elkana Kipkogei

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    Photocatalytic and thermoelectric properties of Cu3 (V, Nb , Ta) Se4 & Cd (G a , A l)2O4: a numerical investigation
    (2020) Rugut, Elkana Kipkogei
    Presently, the scientific community is exploring alternative approaches of generating, conserving and utilizing clean energy in ways that are not only economically viable, but also free from posing health hazards to humanity. This global challenge on energy, forms the basis of this study, whereby the cubic Cu3QSe4(Q = Ta,Nb,V) sulvanites were examined using density functional theory (DFT) approaches, to ascertain if they hold any promising potential in photocatalysis whereby in the presence of light, water is broken down to obtain hydrogen which is a competent and safe energy carrier. On the other hand, thermoelectric materials play an instrumental role in efficient use of energy as they are capable of tapping heat energy that could have otherwise been lost and converts it into electricity. In line with this, Cd(Ga,Al)2O4 spinels were comprehensively studied to examine their applicability as the main component in the design of thermoelectric device. The main goal of this study was to investigate the photocatalytic properties of the sulvanite-type compounds Cu3(V,Nb,Ta)Se4 and thermoelectric properties of spinel oxides Cd(Ga,Al)2O4 in line with clean energy production. In order to achieve these, the following properties were investigated: structural properties of compounds of interest such as lattice constants and Kleinman parameter were determined from relaxed structures. Thereafter, dynamical, energetic and mechanical stability test through phonon, cohesive energy, formation energy and elastic constant calculations were undertaken. Upon verifying their stability, optical study was carried out at the Bethe-Salpeter Equation (BSE) level of approximation to obtain the optical band gap of the sulvanite compounds followed by determination of the absolute band edges done via Mulliken analysis as well as via band gap center approach, to ascertain if Cu3(V,Nb,Ta)Se4 are indeed suitable for single photon water splitting. Considering that photocatalysis occurs at the surface of a material, surface properties of Cu3(V,Nb,Ta)Se4 sulvanites were investigated through calculation of surface energies, vacuum potential and work function among other photocatalytically relevant parameters. At the peak of the study, transport properties of Cd(Ga,Al)2O4 were then determined by solving Boltzmann transport equations to obtain the Seebeck coefficient, charge carrier concentration and lifetime, thermal and electrical conductivity as well as power factor and consequently the figure of merit. These in turn provide an indication whether these spinel oxides possess good thermoelectric properties
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    Numerical simulation of structural, electronic and optical properties of transition metal chalcogenides
    (2017) Rugut, Elkana Kipkogei
    Intensive study on structural, electronic and optical properties of bulk transition metal dichalcogenides and dipnictogenides (MX2; where M = V, Nb and X = S, Se, Te, P) was undertaken. A relative stability test was done to determine the most stable ground state configuration via calculation of total ground state energy and volume which was fitted to the third order Birch-Murnaghan equation of state to extract lattice parameters. Cohesive energies of the above mentioned MX2 compounds and their elemental solids were then computed from which formation energies were acquired based on their respective equations of reaction between reactants and product. Its significance was to aid in determining if a material is energetically stable. Elastic constants were predicted from which mechanical properties i.e bulk, Young’s and shear moduli and consequently Poisson’s ratio were resolved by feeding the stiffness matrix onto online elastic tensor analysis tool which facilitated verification of their mechanical stability based on the well-known Born stability conditions which varies from one crystal system to another, at a later stage phonon dispersion curves were plotted after performing phonon calculation based on phonopy code to verify if the materials of concern are dynamically stable. After a material had fulfilled all the above stability tests, its structural study was initiated using various functionals. Functional that described best the structural properties of each individual compound considered was then applied in exploring its electronic and optical properties whose motivation was to find out the most stable phase as well as gauge if these materials could be used in various fields that suits their mechanical and optical properties. Furthermore, from carefully calculated optical spectra, plasma frequencies were analyzed which indicated the possibility of applying a material in plasmonic related fields. In addition to above, other factors to be considered when selecting a given electrode material that are crucial for optoelectronics are good chemical and thermal stabilities, high transparency and excellent conductivity.