1. College of Physics, Qingdao University, Qingdao 266071, China
2. College of Electronics and Information Engineering, Qingdao University, Qingdao 266071, China
3. Lab of New Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, Qingdao University, Qingdao 266071, China
4. Electronic Ceramics Center, DongEui University, Busan 614-714, South Korea
5. Department of Materials Science/CENIMAT-I3N, Faculty of Sciences and Technology, New University of Lisbon and CEMOP-UNINOVA, Campus de Caparica, 2829-516 Caparica, Portugal