1. Key Laboratory of Engineering Dielectric and Applications (Ministry of Education); Harbin University of Science and Technology; Harbin 150080 China
2. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; 21 Nanyang Link Singapore 637371 Singapore
3. School of Materials Science and Engineering; Nanyang Technological University; Singapore 639798 Singapore
4. Energy Research Institute @NTU (ERI@N); Nanyang Technological University; Singapore 637553 Singapore