1. Electronic Materials Research Laboratory, Key Laboratory of Ministry of Education & International Center for Dielectric Research, Xi’an Jiaotong University, Xi’an 710049, P. R. China
2. Laboratoire de Physico-Chimie de l’Etat Solide, ICMMO, CNRS-UMR 8182, Bâtiment 410 -Université Paris-Sud XI, 15 rue
Georges Clémenceau 91405 Orsay Cedex, France
3. School of
Photoelectric Engineering, Xi’an Technological University, Xi’an 710021, P. R. China