1. Key Laboratory of Engineering Dielectric and Applications (Ministry of Education) School of Electrical and Electronic Engineering Harbin University of Science and Technology Harbin 150080 P. R. China
2. Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore
3. Department of Materials Science and Engineering Zhejiang University Hangzhou 310027 P. R. China