1. Key Laboratory of Engineering Dielectrics and Its Application Ministry of Education Harbin University of Science and Technology Harbin 150080 P. R. China
2. School of Electrical and Electronic Engineering Harbin University of Science and Technology Harbin 150080 P. R. China
3. Electronic Materials Research Laboratory Key Lab of Education Ministry Xi'an Jiaotong University Xi'an 710049 P. R. China