1. Energy Storage and Conversion Devices Laboratory Department of Physics; Bharathiar University; Coimbatore - 641 046, Tamil Nadu India
2. present address: Department of Physics; PSGR Krishnammal College for Women; Coimbatore 641 004, Tamil Nadu India
3. Faraday Materials Laboratory Materials Research Centre; Indian Institute of Science; Bangalore India
4. Semiconductor Electronics Department; Lviv Polytechnic National University; 12 Bandera Street Lviv 79013 Ukraine