Europhys. Lett.
Volume 69, Number 4, February 2005
Page(s) 556 - 562
Section Condensed matter: structure, mechanical and thermal properties
Published online 21 January 2005
Europhys. Lett., 69 (4), pp. 556-562 (2005)
DOI: 10.1209/epl/i2004-10387-x

Pressure-induced homothetic volume collapse in silicon clathrates

A. 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 $\chem{Ba}$-doped silicon clathrate $\chem{Ba_8Si_{46}}$ 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 $\un{GPa}$. This transformation is characterized by the homothetic contraction of the silicon cages containing the $\chem{Ba}$ atoms. This transition is preceded by a change in the electronic structure at 5 $\un{GPa}$ 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 $\un{\AA}$. At the highest studied pressure of 49 $\un{GPa}$, 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.

© EDP Sciences 2005