1. College of Chemistry and Materials Engineering, Bohai University, Jinzhou 121000, P. R. China
2. State Key Lab Superhard Mat, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R China
3. Key Laboratory of New Energy and Rare Earth Resource Utilization of State Ethnic Affairs Commission, College of Physics and Materials Engineering, Dalian Minzu University, 18 Liaohe West Road, Dalian 116600, P. R. China