1. CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
2. College of Physics and Optoelectronics Engineering Shenzhen University, Nanhai Avenue 3688, Shenzhen, Guangdong 518060, P. R. China
3. State Key Laboratory of Advanced Refractories, Sinosteel Luoyang Institute of Refractories Research Company, Limited, Luoyang, Henan 471039, P. R. China
4. Department of Materials Science and Engineering, University of Ioannina, Ioannina GR-451 10, Greece