ETD Collection

Permanent URI for this collectionhttps://wiredspace.wits.ac.za/handle/10539/104


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Author: search.filters.author.Manyali, George Simiyu

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    A computational study of layered and superhard carbon-nitrogen material
    (2015-02-04) Manyali, George Simiyu
    The process of the computational discovery of materials for future technologies is a combination of numerical techniques and general scientific intuition to select elements and combine in order to form novel types of materials. Modern ab initio methods based on density functional theory are capable of predicting with a high level of accuracy the most stable ground state atomic configurations of any given material. Once the ground state configurations are established, the electronic, optical and mechanical properties of the novel bulk nitrides may be determined. Electronic properties of C3N4, CN2, SiN2, GeN2, C2N2(NH), Si2N2(NH), Ge2N2(NH) and Sn2N2(NH) are analysed by computing the Kohn-Sham band structures. The optical properties are investigated by calculating the real and the imaginary parts of the frequency-dependent dielectric constant. The mechanical properties are determined by calculating elastic constants, Young’s modulus, Poisson’s ratio, Vickers hardness, shear and bulk moduli.
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    Ab-initio study of elastic and structural properties of layered nitride materials
    (2012-06-14) Manyali, George Simiyu
    Layered nitride materials in the form of Carbon nitride (C3N4) was speculated nearly 22 years ago. It has various structural forms ranging from layered graphitic to superhard structures. Using first principles calculations based on density functional theory, the structural and elastic properties of these phases are determined. Elastic constants, bulk and shear moduli of cubic phases are compared to that of diamond. From the work it is evident that, although the compressibility of some of the superhard phases may be better than diamond, the shear modulus indicates that C3N4 is not harder than diamond in contrast to what has been speculated ealier. The graphitic hexagonal, rhombohedral as well orthorhombic phases are soft as indicated by their bulk and shear moduli, which are similar to that of graphite. Other elastic properties such as the Young modulus and Poisson’s ratio as well as the Raman and infrared vibrational frequencies are also presented in this dissertation