High pressure synthesis and crystal structure of two forms of a new tellurium–silicon clathrate related to the classical type I

• Published in: Solid state sciences Vol. 6; no. 5; pp. 401 - 411
• Main Authors: Jaussaud, N., Toulemonde, P., Pouchard, M., San Miguel, A., Gravereau, P., Pechev, S., Goglio, G., Cros, C.
• Format: Journal Article
• Language: English
• Published: Paris Elsevier Masson SAS 01.05.2004; Elsevier
• Subjects: Chemical Sciences; Clathates; Condensed matter: structure, mechanical and thermal properties; Crystal structure; Crystalline state (including molecular motions in solids); Exact sciences and technology; High pressure synthesis; Material chemistry; Physics; Silicon; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Tellurium; Theory of crystal structure, crystal symmetry; calculations and modeling; Clathates; Silicon; High pressure synthesis; Tellurium; Crystal structure; Coordination number; Crystal form; Space groups; XRD; Heat treatments; Clathrates; High pressure; Monocrystals; Synthesis; Substitutional impurities; Crystallographic site; Elongation (mechanics)
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2004.02.010

Two new clathrate-type structures have been identified in the samples obtained by high pressure–high temperature treatment of appropriate mixtures of elemental silicon and tellurium at 5 GPa and 1200 °C for 60 min reaction time. They are both related to the classical type I silicon clathrate, G 8Si 46 ( G=guest species). The corresponding structures have been solved by X-ray single crystal diffraction analysis. They proved to correspond to a cubic and rhombohedral forms of the same compound, Te 16Si 38 (or more precisely Te 8@(Si 38Te 8)), in which eight extra tellurium atoms are substituted for silicon ones in the 16i crystallographic sites of the parent structure. In the cubic form, the space group is reduced from Pm-3 n to P-43 n, and the formation of strong bonds between the Te atoms at the centre of the tetrakaidecahedral cages and one or two silicon atoms of the surrounding cage is clearly observed, which is followed by a decrease of the coordination number of the Te atoms in substitutional position from 4 to 3. In the more distorted rhombohedral form, the 16i and 24k sites of the parent structure are both split in four sites. The formation of strong bonds involving the Te atoms at the centre of the tetrakaidecahedral cages is confirmed, but the main characteristic comes from the formation of another kind of strong bonds involving the Te atoms at the centre of the dodecahedral cages. These bonds are at the origin of the elongation of the structure along the [111] direction, which corresponds to the polar axis. Graphic