<p>In many materials, changes in chemical composition, pressure or temperature can induce metal to insulator transitions. It is recently observed in yttrium hydride, for example, changes from a shiny mirror (YH<sub>2</sub>) to a transparent window (YH<sub>3</sub>), which has important technological application in optical devices. We have tuned the above transition by choosing <i>pressure</i> instead of composition. Our predicted finding is confirmed by recent experiments and opens a new way to design optical switches.</p><p>The unique role that gold plays in society is to a large extent related to the fact that it is the most <i>noble</i> of all metals.We have studied the noble nature of gold by choosing <i>pressure</i> as tool. Our prediction shows that gold transforms from a face centered cubic to an hexagonal closed packed phase above 200 GPa whereas platinum, another noble metal, does not show any phase transition up to 500 GPa. This prediction has also been confirmed by experiments suggesting that platinum is more noble than gold.</p><p>The growing concern about climate change and fossil fuel availability, the direct conversion of solar irradiation into electricity appears to be an ideal alternative to conventional energy sources. Power generation by solar cells is a direct method of solar energy conversion. We report a new cubic phase of TiO<sub>2</sub> which can be stabilized at ambient conditions. This phase has an absorption three or four orders of magnitude larger than the conventional state-of-the-art solar cell based on anatase TiO<sub>2</sub>. Therefore, we are introducing a well established material with a new structure for future generation solar cells. The same effect is also observed in cubic SnO<sub>2</sub>.</p><p>Electronic and optical properties of other materials such as Be<sub>x</sub>Zn<sub>1-x</sub>Te, RuO<sub>2</sub> and IrO<sub>2</sub> are also studied in present thesis. In particular, for Be<sub>x</sub>Zn<sub>1-x</sub>Te, we have used composition as a tool to tune the optical properties.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:uu-6923 |
| Date | January 2006 |
| Creators | Souza de Almeida, Jailton |
| 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 | Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 192 |
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