1. Electronic Materials Research Laboratory; Key Laboratory of the Ministry of Education and International Center for Dielectric Research; Xi'an Jiaotong University; Xi'an 710049 China
2. Micro-Optoelectronic Systems Laboratories; Xi'an Technological University; Xi'an 710032 China
3. National Synchrotron Radiation Laboratory; University of Science and Technology of China; Hefei 230029 China
4. State Key Laboratory of New Ceramics and Fine Processing; Department of Materials Science and Engineering; Tsinghua University; Beijing 100084 China