1. Department of Electronics Engineering, Indian School of Mines, Dhanbad 826004, India
2. Department of Electronics Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India
3. Department of Ceramic Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India
4. School of Physics, University of Hyderabad, Hyderabad 500 046, India