1. Key Laboratory of New Energy and Rare Earth Resource Utilization of State Ethnic Affairs Commission, School of Physics and Materials Engineering, Dalian Minzu University, 18 Liaohe West Road, Dalian 116600, P. R. China.
2. School of Metallurgy, Northeastern University, Shenyang 110819, China.
3. School of Science, Minzu University of China, Beijing, China.