Anatase-Rutile Phase Transformation of Cu2+ Doped TiO2 in a Non-Reducing Atmosphere

Abstract

The anatase-rutile phase transformation of TiO2 containing various Cu2+ amounts of Cu ions was investigated in argon atmosphere by means of X ray diffraction and electron spin resonance spectroscopy. The samples were prepared by the sol-gel method from titanium(IV) isopropoxide and copper(II) nitrate. The amorphous samples were calcined in argon atmosphere for 2 h at different temperatures. In the presence of Cu2+, the anatase-rutile transition temperature is lower than the corresponding one in pure TiO2. The transformation in argon atmosphere changes the transition temperatures due to the spontaneous reduction of Cu2+ and Ti4+ ions to metallic copper and Ti3+ respectively. The broadening of the electron spin resonance spectra from this ion show that Ti3+ ions are present in different sites into the TiO2 lattice. This are confirmed by electron spin resonance and allowed us to follow the phase transformation in detail.