High pressure x-ray diffraction study of the volume collapse in Ba24Si100 clathrate

Pierre Toulemonde (1) , D. Machon (2) , A. San Miguel (2) , M. Amboage (3, 4)

1 NEEL - MRS - Matériaux, Rayonnements, Structure
2 LPMCN - Laboratoire de Physique de la Matière Condensée et Nanostructures
3 ESRF - European Synchrotron Radiation Facility
4 DIAMOND Light source

The high pressure stability of the silicon type-III clathrate Ba24Si100 has been studied by x-ray diffraction (XRD) up to a maximum pressure of 37.4 GPa. The high pressure behavior of this Si type-III clathrate appears to be analogous to the structural type-I parent Ba8Si46. An isostructural volume collapse is observed at ~23 GPa, a value higher than for Ba8Si46 (13-15 GPa). The crystallinity of the structure is preserved up to the maximum attained pressure without amorphization, which appears to be in contradiction with the interpretation given in a Raman spectroscopy study [Shimizu et al., Phys. Rev. B 71, 094108 (2005)]. Nevertheless, the XRD analysis shows the appearance of a type-III disordered nanocaged-based crystalline structure after the volume collapse. Moreover, we find that the volume collapse transformation is (quasi)reversible after pressure release. Additionally, a low pressure transition first evidenced by Raman spectroscopy is also observed in our XRD study at 5 GPa: The variation of the isotropic thermal factors of Ba atoms shows a clear discontinuity at this pressure while the average positions of Ba atoms remain identical.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

Pierre Toulemonde, D. Machon, A. San Miguel, M. Amboage. High pressure x-ray diffraction study of the volume collapse in Ba24Si100 clathrate. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2011, 83, pp.134110. ⟨10.1103/PhysRevB.83.134110⟩. ⟨hal-00987187⟩