K7.62(1)Si46 and Rb6.15(2)Si46: Two Structure I Clathrates with Fully Occupied Framework Sites
| Autor: | Ganesh K. Ramachandran, Paul F. McMillan, Otto F. Sankey, Jianjun Dong |
|---|---|
| Rok vydání: | 2000 |
| Předmět: |
Stereochemistry
Chemistry Hypervalent molecule Crystal structure Condensed Matter Physics Semimetal Electronic Optical and Magnetic Materials Inorganic Chemistry Metal Crystallography Electrical resistivity and conductivity visual_art Vacancy defect Atom Materials Chemistry Ceramics and Composites visual_art.visual_art_medium Physical and Theoretical Chemistry Stoichiometry |
| Zdroj: | Journal of Solid State Chemistry. 154:626-634 |
| ISSN: | 0022-4596 |
| DOI: | 10.1006/jssc.2000.8906 |
| Popis: | We report here the synthesis and structural characterization of two Structure I clathrates in the K–Si and Rb–Si systems. As observed previously for Na 8 Si 46 , the alkali-Si clathrates are fully stoichiometric at the framework sites, i.e., devoid of framework vacancies. This is in sharp contrast to the analogous K–Ge, Rb–Ge, and Rb–Sn, (K,Cs)–Sn, and Cs–Sn systems, where two vacancies are formed predominantly at one-third of the crystallographic 6 c tetrahedral sites (the formation of vacancies is rationalized to remove the tetrahedral atom of its hypervalency). This result is understood generally in terms of weaker Tt – Tt ( Tt (tetrelide)=Si, Ge, Sn) bonding as one descends the periodic table. Also observed are metallic conductivities for both K 8 Si 46 and Rb 6 Si 46 , substantiating further the absence of vacancies — the “extra” electrons from the guest atoms participate in the conduction bands of the Si network, resulting in conductivities typical of semimetals. This is contrasted with the semiconducting behavior of the vacancy bearing K 8 Ge 44 (K 8 Ge 44 □ 2 ). |
| Databáze: | OpenAIRE |
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