a
College of Science, Xi'an University of Architecture and Technology, Xi'an, China
E-mail: gaodangli@163.com
b
Electronic Materials Research Laboratory (EMRL), Key Laboratory of Education Ministry, International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an, China
c
College of Physics and Electronic Information Engineering, Qinghai Nationalities University, Xining, China
d
College of Physics and Information Technology, Shaanxi Normal University, Xi'an, China
E-mail: hrzheng@snnu.edu.cn