1. Center for Advanced Materials and Energy; Xihua University; Chengdu Sichuan 610039 PR China
2. Key Laboratory of Special Materials Preparation and Control; Xihua University; Chengdu Sichuan 610039 PR China
3. State Key Laboratory of Electrical Insulation and Power Equipment; Xi'an Jiaotong University; Xi'an Shaanxi 710049 PR China