1. Beijing National Laboratory for Molecular Sciences State Key Laboratory of Rare Earth Materials Chemistry and Applications College of Chemistry and Molecular Engineering, Peking University 100871 Beijing P. R. China
2. College of Materials Science and Engineering Guilin University of Technology 541004 Guilin P. R. China
3. Neutron Scattering Laboratory Department of Nuclear Physics China Institute of Atomic Energy 102413 Beijing P. R. China