1. State Key Laboratory of New Ceramics and Fine Processing
2. School of Materials Science and Engineering
3. Tsinghua University
4. 100084 Beijing
5. P. R. China
6. Department of Physics
7. South University of Science and Technology of China
8. Shenzhen 518055
9. China
10. Department of Materials Science and Engineering
11. Northwestern University
12. Evanston
13. USA
14. Max Planck Institute for Chemical Physics of Solids
15. Dresden
16. Germany