1Key Laboratory of Instrumentation Science, and Dynamic Measurement, Ministry of Education, Science and Technology on Electronic Test and Measurement Laboratory, Taiyuan 030051 (China), Fax: (+86) 351-3559638
2School of Material science and engineering, North University of China, Taiyuan 030051, China
3State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing, 100084, China