Preparation and characterization of nanocrystalline metal oxide powders

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Spintronics is a rapidly growing field of research in multidisciplinary level and intensified by a strong synergy between breakthroughs in basic science and industrial applications. Particularly, in the area of semiconductor spintronics, the realization of materials that combine semiconducting behavior with robust magnetism has long been a dream of material physics. One of the precondition for semiconductor spintronics is the use of ferromagnetic semiconductors with large Curie temperature (TC) above room temperature. Thus, the topic of diluted magnetic semiconductors (DMS) has received extensive interest. In this thesis work, we have made an attempt to prepare various nanocrystalline oxides such as NiO, ZnO and TiO2 using ball mill process in high energy planetary ball mill. Systematic studies of evolution of nanocrystalline structure, vibrational, electronic, magnetic, resonance and optical properties of NiO, ZnO and TiO2 powders were carried out to understand the effect of milling. The milled powders were subsequently heat treated at elevated temperatures under air atmosphere to understand origin of ferromagnetism in these nanocrystalline oxides. For comparative study, NiO nanoparticles were prepared by sol-gel method with different molar concentrations and annealed at different annealing temperatures, and characterized. Structural studies of milled powders revealed that the average crystal size decreases with increasing milling time. The existence of defects, size reduction, oxidization of Ni2+ to Ni3+ due to breaking of Ni2+-O2--Ni2+ super-exchange interaction could be evidently seen through Raman and X-ray photoelectron spectroscopy (XPS) spectra. Similarly, the development of defects due to oxygen vacancies and/or Zn interstitials in ZnO milled powders has been observed from Raman and XPS spectra
Supervisor: Perumal Alagarsamy