<p>This thesis is based on a study of five distinct intermetallic systems with the aim of expanding the general knowledge of aperiodically modulated crystal structures. Families of compounds that contain a variety of superstructures together with incommensurately modulated structures have been investigated mainly by means of single crystal X-ray diffraction and higher dimensional structure models.</p><p>A uniform (3+1)-dimensional structure for Bi-Se phases was developed with the composition as a single variable. The structure description is based on a cubic NaCl type structure with homoatomic layer stackings. It is shown by computational modelling that the formation energies of bismuth selenides with more than 40 at. % Bi are close to zero, a result that supports the idea of a continuous series of stackings corresponding to an ordered solid solution of Bi in Bi<sub>2</sub>Se<sub>3</sub>.</p><p>The Nowotny chimney-ladder structures are described with a (3+1)-dimensional composite structure, valid for all such compounds regardless of the included elements, the composition or the valence electron concentration. A new member is added to this family by the ZrBi<sub>1.62</sub> compound. The modulation is believed to arise as a secondary effect of the criteria of a fixed electron count.</p><p>A symmetry analysis is presented for the <i>RE</i><sub>1+ε</sub>(MB)<sub>4</sub> (<i>RE</i> = rare earth elements, M = iron metal elements) family of compounds and a uniform (3+1)-dimensional composite structure description has been developed. The modulation may be due to the presence of unusually short contacts between the <i>RE</i> channel atoms, giving rise to a rotational modulation of the (MB)<sub>4</sub> tetraederstern chains.</p><p>A (3+1)-dimensional incommensurate structure has been determined for the novel δ<sub>1</sub> – CoZn compound. The structure displays a unique assembly of fused icosahedra and the modulation is induced by geometric strain.</p><p>The structure of the K(PtSi)<sub>4</sub> compound was re-determined. Despite a close kinship with the <i>RE</i><sub>1+ε</sub>(MB)<sub>4</sub> compounds, this structure is not modulated.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-312 |
| Date | January 2004 |
| Creators | Lind, Hanna |
| Publisher | Stockholm University, Department of Physical, Inorganic and Structural Chemistry, Stockholm : Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
Page generated in 0.0018 seconds