"Rattling ‘guest’ impurities in Si and Ge clathrate semiconductors"

Koushik Biswas, Emmanuel Nenghabi, Charles Myles

Research output: Contribution to journalArticlepeer-review

Abstract

In addition to their ground state, diamond structure, Si, Ge and Sn can form crystalline solids called clathrates. As in the diamond structure, in the clathrates, the Group IV atoms are tetrahedrally coordinated and sp3 covalently bonded to their neighbors. However, the clathrates contain pentagonal atomic rings and have open-framework lattices containing 20-, 24- and 28-atom ‘‘cages’’. There are two clathrate lattices: Type I, a SC lattice with 46 atoms per unit cell and Type II, a FCC lattice with 136 atoms per cubic cell. The pure clathrates are semiconductors. The cages can contain weakly bound impurities (‘‘guests’’), usually alkali or alkaline earth atoms. The choice of guest may be used to tune the material properties. The guests are electronic donors, but because of their weak bonding, they have small effects on the electronic band structures. However, they can produce low frequency vibrational (‘‘rattling’’) modes which can strongly affect the vibrational properties. Some gue
Original languageEnglish
Pages (from-to)695-698
JournalPhysica B: Condensed Matter
StatePublished - Dec 15 2007

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