A New Class of Low Compressibility Materials: Clathrates of Silicon and Related Materials

We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.