Pressure-induced homothetic volume collapse in silicon clathratesA. San Miguel1, A. Merlen1, P. Toulemonde1, T. Kume1, S. Le Floch1, A. Aouizerat1, S. Pascarelli2, G. Aquilanti2, O. Mathon2, T. Le Bihan2, J.-P. Itié3 and S. Yamanaka4
1 Laboratoire de Physique de la Matière Condensée et Nanostructures Université Claude Bernard Lyon-1 and CNRS - 43 Bvd. du 11 Novembre 1918 69622 Villeurbanne, France
2 European Synchrotron Radiation Facility - BP 220, 38043 Grenoble, France
3 Physique des Milieux Condensés, Université P. and M. Curie and CNRS - France
4 Department of Applied Chemistry, Faculty of Engineering, Hiroshima University Higashi-Hiroshima 724, Japan
received 24 September 2004; accepted in final form 10 December 2004
published online 21 January 2005
The high-pressure properties of the -doped silicon clathrate have been investigated combining X-ray diffraction and X-ray absorption spectroscopy. A pressure-induced isostructural phase transition associated with an important volume collapse takes place at 11.5-14 . This transformation is characterized by the homothetic contraction of the silicon cages containing the atoms. This transition is preceded by a change in the electronic structure at 5 in good agreement with Raman spectroscopy observations (T. KUME et al. , Phys. Rev. Lett., 90 (2003) 155503) that it is also of isostructural nature. The cage structure is preserved through the phase transitions allowing to obtain tetrahedral silicon with record interatomic distances as low as 2.13 . At the highest studied pressure of 49 , the structure becomes irreversibly amorphous. The physical origin of the homothetic isostructural transitions is discussed.
61.50.Ks - Crystallographic aspects of phase transformations; pressure effects.
61.48.+c - Fullerenes and fullerene-related materials.
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