1. High Pressure Research Center, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw, Poland
2. Institute of Experimental Physics, Warsaw University, Hoża 69, 00-681 Warsaw, Poland
3. CEA-Grenoble, Departement de Recherche Fondamentale sur la Matiere Condensée SP2M, 17 Rue des Martyrs, 38054 Grenoble Cedex 9, France