1. School of Rare Earths University of Science and Technology of China, Hefei 230026, P. R. China
2. Key Laboratory of Rare Earths, Chinese Academy of Sciences, Ganjiang Innovation Academy, Chinese Academy of Sciences, Ganzhou 341000, P. R. China
3. State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China