[1] Univ Tours, EA CIME 2098, F-37200 Tours, France
[2] RAS, LF Vereshchagin Inst High Pressure Phys, Troitsk 142190, Moscow Region, Russia
[3] Univ Paris 06, CNRS, UMR 7047, F-75252 Paris, France
[4] CNRS, Ecole Mines Paris, UMR 7633, Ctr Mat, F-91003 Evry, France