@article {Ramachandran:2000:0953-8984:4013, author = "Ramachandran G.K.", author = "McMillan P.F.", author = "Deb S.K.", author = "Somayazulu M.", author = "Gryko J.", author = "Dong J.", author = "Sankey O.F.", title = "High-pressure phase transformation of the silicon clathrate Si136", journal = "Journal of Physics: Condensed Matter", volume = "12", year = "2000", abstract = "

The compressional behaviour of a new expanded form of silicon, the cubic Si136 clathrate, is studied by energy dispersive x-ray diffraction in a diamond anvil cell experiment. The ambient temperature bulk modulus and its pressure derivative are determined to be [iopmath latex="$K_0=90(3)$"] K0 = 90(3) [/iopmath]  GPa and [iopmath latex="$K_0'=5.2(8)$"] K0' = 5.2(8) [/iopmath] , in agreement with LDA theoretical calculations. At pressures between 8 and 10 GPa, the structure transforms into the thermodynamically stable [iopmath latex="$\beta$"] [/iopmath] -Sn phase. This behaviour is analogous to that of diamond-structured silicon. However, the metastable transition from Si136 to the [iopmath latex="$\beta$"] [/iopmath] -Sn structure should occur at a much lower pressure (3-4 GPa), from consideration of free energy-pressure relations. The observation can be related to the absence of a convenient low-energy pathway for the IV- to VI-fold coordination change involved in the transition from Si136 to [iopmath latex="$\beta$"] [/iopmath] -Sn.

", pages = "4013-4020(8)", url = "http://www.ingentaconnect.com/content/iop/jphyscm/2000/00000012/00000017/art00308" }