<p>This thesis presents a theoretical study of bulk materials using <i>ab initio</i> methods based on the density functional theory (DFT).</p><p>Crystallographic structural phase transformations and phase stability for 5f-dioxides, ABO<sub>3</sub> perovskites, and ABO<sub>4</sub> compounds have been extensively studied. Different approaches such as static total energy calculations, elastic stability and dynamical stability (phonon calculations) criteria have been used to determine the phase stability. As a special case, the lattice dynamics of solid Xe has been studied as a function of pressure.</p><p>Dielectric functions and optical constants have been calculated for solar energy cell system CuIn<sub>1-x</sub>Ga<sub>x</sub>Se<sub>2</sub> with concentrations x=0, 0.25, 0.5 and 1.0 as well as for C<sub>60</sub>, PbWO<sub>4 </sub>and δ-AlOOH. The absorption coefficient provides information about the optimum solar energy conversion efficiency. We have derived absorption coefficients for a number of compounds. Comparisons between the calculated and experimental dielectric functions and absorption coefficients have been made.</p><p>The main part of this thesis focuses on the nanolayered ternary compounds M <sub>N+1</sub>AX<sub>N </sub>(MAX), where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N. These ternary carbides and nitrides combine unusual properties of both metals and ceramics. They exhibit high hardness, but fully reversible plasticity, and negligible thermoelectric power. These excellent properties make the MAX phases another new class of materials with versatile technological applications. Our work presents a systematic study of the electronic, bonding, elastic and optical properties of the MAX phases. A new MAX phase-Ti<sub>4</sub>SiC<sub>3, </sub>is calculated to be stable, and at the same time also been synthesized by experimentalists. Surface energy calculations have also been performed for the (0001) surface of the Ti-Si-C system. The general relations between the electronic structure and materials properties of the MAX phases have been elaborated in the thesis.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-4274 |
| Date | January 2004 |
| Creators | Li, Sa |
| Publisher | Uppsala University, Department of Physics, Uppsala : Acta Universitatis Upsaliensis |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
| Relation | Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1104-232X ; 982 |
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