1. Research Institute for New Materials Technology, Chongqing University of Arts and Sciences, Chongqing 402160, P. R. China
2. School of Materials Science and Engineering, Chongqing University of Technology, Chongqing 400054, P. R. China
3. Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, P. R. China