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Defects and defect processes in ultra-hard nitrides

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dc.contributor.advisor Lowther JE en
dc.contributor.author Mosuang TE en
dc.date.accessioned 2016-09-22T11:14:09Z
dc.date.available 2016-09-22T11:14:09Z
dc.date.created 2000 en
dc.date.submitted 2003 en
dc.identifier.uri http://hdl.handle.net/20.500.11892/106327
dc.description.abstract This thesis addresses, as its primary subject matter, the modelling of new ultra-hard materials. Most specifically, the influence of defects in affecting the transfomation of h-BN to c-BN has been investigated using the supercell approach. The properties of simple B, C, N, and O defects in both the hexagonal and cubic phases are shown to facilitate the phase transition. <br><br> We investigate the various properties through ab-initio plane wave pseudopotential calculations within the local density approximation. Ionic relaxations based on Hellman-Feynman forces have been included throughout whenever the various defects are analysed. Various defects considered are located at substitutional, antisite, and interstitial positions including split, bond-centered, and hexagonal. <br><br> These calculations show that all the B and C associated defects have high formation energies relative to those of vacancies V<sub>B</sub> and V<sub>N</sub>. For instance, in N-rich conditions, substitutional C<sub>B</sub> in the cubic phase has a formation energy equal to that for the vacancy, V<SUB>B</SUB>, its defect total energy is greater than the energy difference of defect free material. So B and C defects are not likely to cause a ft-BN to c-BN transformation. N and O defects have the lowest formation energies relative to the vacancies, and may therefore affect the h-BN to c-BN phase transition. The defect total energy is low suggesting that the N and O defect are much more soluble in both the hexagonal and the cubic phases. This is consistent with the experimental findings of nitrogen interstitials and vacancies in the hexagonal BN thin films grown by the ion-bombardment technique. The results suggest that a possible role in synthesis of c-BN is to dope the hexagonal BN with larger amounts of N and/or O defects. en
dc.language English en
dc.title Defects and defect processes in ultra-hard nitrides en
dc.type Doctoral degree en
dc.description.degree PhD (Science) en

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