“Electronic and Vibrational Properties Framework-Substituted Type II Si Clathrates”

Koushik Biswas, Charles Myles

Research output: Contribution to journalArticle

Abstract

Framework substitution has not been widely reported among the type-II group-IV clathrates. We have performed a theoretical study of the Cs8Ga8Si128 and Rb8Ga8Si128 clathrates, using the local-density approximation LDA to density-functional theory. In Rb8Ga8Si128 and Cs8Ga8Si128, eight Si atoms are substituted by Ga at the 8a crystallographic sites of the framework. We predict that both Rb8Ga8Si128 and Cs8Ga8Si128 are semiconductors with LDA indirect band gaps in the range of 0.73–0.77 eV. Similar substitution with Ge instead of Ga rendered the materials metallic. We have compared the electronic and vibrational properties of these Ga-substituted materials with those of the partially filled Rb8Si136 and completely filled Na16Rb8Si136 clathrates. The phonon-dispersion curves show low-frequency guest “rattling” modes for each material. We have used these results to estimate the temperature-dependent values of the isotropic mean-square displacement amplitude Uiso for the various guest atom
Original languageEnglish
Pages (from-to)245205-1 to 245205-7
JournalPhysical Review B
StatePublished - Jun 13 2007

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