1. Electronic Materials Research Laboratory Key Laboratory of the Ministry of Education & International Center for Dielectric Research Shaanxi Engineering Research Center of Advanced Energy Materials and Devices School of Electronic Science and Engineering Xi'an Jiaotong University Xi'an Shaanxi 710049 P. R. China
2. College of Materials Science and Engineering Xi'an University of Science and Technology Xi'an Shaanxi 710054 P. R. China