An experimental investigation was made involving the synthesis of nepheline (NaAlSiO4) under varying conditions of temperature and water pressure 2022-2130 for each synthesized charge was obtained using x-ray diffraction methods. It was found that the results of the individual runs provided an erratic lattice parameter variation with temperature in the range 500 to 800 degrees Celsius. However, a least squares curve indicates that no change in lattice parameters in the low-nepheline polymorph occurs with temperature of formation, for 95 percent probability. / Thesis / Master of Science (MS)

<p> The lattice parameters and crystal symmetry of silane (SiH4) are examined by X-ray powder diffraction. Comparisons are made with vibrational spectrum and birefringence measurements and with respect to an order-disorder transition between the two solid phases of silane.</p> / Thesis / Master of Science (MSc)

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Made available in DSpace on 2014-10-09T12:47:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:26Z (GMT). No. of bitstreams: 1 08349.pdf: 3194587 bytes, checksum: 65eb4db04988a87107998b9237835cdd (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Precession photography was used to determine the lattice parameters, the crystal system, the space group and the structure of an artificial Sr-labradorite of composition: Ab27, SrAn73. C= 7.107Å, Ɣ= 90 degrees, β= 115.834 degrees. The crystal system is monoclinic, space group= C2/ m and structure is albite type, reflections being restricted to the 'a' type. The abundance, lithophile characteristics and appropriate ionic radii of elements in Groups IA and IIA are the factors governing their presence as cations of feldspars in nature. The structures of feldspars are discussed as a function of the relative proportion of cations of a charge of +1 and +2. The crystal symmetry (i.e. monoclinicity or triclinicity) is discussed as a function of the ionic radius of the cation. / Thesis / Bachelor of Science (BSc)

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Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotenial method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations, the empirical pseudopotential method is also used in this work. Pseudopotentials 'or each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k,p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular, valence band offsets for nitride heterojunctions are calculated, and a strong forward-backward asymmetry in the band offset is found, in good agreement with other results in the literature.