1. Electronic Materials Research Laboratory; Key Laboratory of the Ministry of Education & International Center for Dielectric Research; Xi'an Jiaotong University; Xi'an Shaanxi 710049 China
2. School of Science; Xi'an University of Architecture & Technology; Xi'an Shaanxi 710055 China
3. School of Science; Xi'an Polytechnic University; Xi'an Shaanxi 710048 China