title: Structural stability and phase transitions in K8Si46 clathrate under high pressure.
abstract: The structural stability of type-I K8Si46 clathrate has been investigated at high pressure by synchrotron x-ray diffraction. In contrast to that observed in the Na-doped structure-II analogue [A. San-Miguel, Phys. Rev. Lett. 83, 5290 (1999)]], no phase separation into the beta-Sn Si structure was identified at 11 GPa. Instead, K8Si46 is found to undergo a transition to an isostructural positional disordered phase at around 15 GPa. Ab initio phonon band structure calculations reveal a novel phenomenon of phonon instabilities of K atoms in the large cavities is responsible for this transition. Above 32 GPa, the new structure transforms into an amorphous phase.
authors.affiliation: Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6. John.Tse@nrc.ca
authors.forename: John S
authors.initials: JS
authors.lastname: Tse
authors.forename: Serge
authors.initials: S
authors.lastname: Desgreniers
authors.forename: Zhi-Qiang
authors.initials: ZQ
authors.lastname: Li
authors.forename: Michael R
authors.initials: MR
authors.lastname: Ferguson
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kawazoe