title: Framework contraction in Na-stuffed Si(cF136).
abstract: Systematic crystal structure refinements from powder X-ray diffraction data as well as density functional theory calculations demonstrate that the silicon clathrate II Si(cF136) exhibits a lattice contraction as Na is introduced solely into the Si(28) cages. When the Si(20) cages, in addition, begin to be filled with Na, a contrasting lattice expansion results. The nonmonotonic structural response to filling is an indication of markedly dissimilar guest-framework interactions for Na@Si(20) and Na@Si(28).
authors.affiliation: Department of Physics, University of South Florida, Tampa, Florida 33620, USA.
authors.forename: Matt
authors.initials: M
authors.lastname: Beekman
authors.forename: Emmanuel N
authors.initials: EN
authors.lastname: Nenghabi
authors.forename: Koushik
authors.initials: K
authors.lastname: Biswas
authors.forename: Charles W
authors.initials: CW
authors.lastname: Myles
authors.forename: Michael
authors.initials: M
authors.lastname: Baitinger
authors.forename: Yuri
authors.initials: Y
authors.lastname: Grin
authors.forename: George S
authors.initials: GS
authors.lastname: Nolas