1. Faculty of Science, Yibin University, Yibin 644000, P. R. China
2. Faculty of Science, Key Laboratory of Computational Physics of Sichuan Province, Yibin University, Yibin 644000, P. R. China
3. Sichuan Province Engineering Technology Research, Center of Powder Metallurgy, Chengdu University, Chengdu 610106, P. R. China