1. CAS Key Laboratory of Materials for Energy ConversionShanghai Institute of CeramicsChinese Academy of Sciences Shanghai 200050 P. R. China
2. State Key Laboratory of High Performance Ceramics and Superfine Microstructure Shanghai Institute of CeramicsChinese Academy of Sciences Shanghai 200050 P. R. China
3. Centre of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China