Abstract
Anatase and rutile TiO2-δ powders are synthesized by the sol-gel method. The hysteresis loops and the zero field-cooled and the field-cooled magnetization curves indicate that reduced TiO2-δ powders exhibit the room-temperature ferromagnetism that becomes stronger with prolonging annealing time in H2/Ar mixture. Analysis of Ti 2p x-ray photoelectron spectroscopy spectra indicates that Ti ions are all in the Ti4+ state and that Ti3+ or Ti2+ ions do not exist in all samples. In addition, analysis of O 1s x-ray photoelectron spectroscopy spectra indicates that the concentration of oxygen vacancies increases with prolonging annealing time. Analysis of ultraviolet-visible absorption spectra also further confirms that the concentration of oxygen vacancies increases with prolonging annealing time. These results indicate that ferromagnetism in pure TiO2-δ powders stems from oxygen vacancies. The possible mechanism on ferromagnetism is discussed.
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