1. Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai 201203 P. R. China
2. Department of Physics Fudan University Shanghai 200433 P. R. China
3. State Key Laboratory of Superhard Materials Jilin University Changchun 130012 P. R. China
4. High Pressure Synergetic Consortium (HPSynC) Geophysical Laboratory Carnegie Institution of Washington Argonne IL 60439 USA
5. State Key Laboratory of Inorganic Synthesis and Preparative Chemistry College of Chemistry Jilin University Changchun 130012 P. R. China