LATTICE DEFORMATION AND PHASE TRANSFORMATION FROM NANO-SCALE ANATASE TO NANO-SCALE RUTILE TiO_2 PREPARED BY A SOL-GEL TECHNIQUE

1. Introduction Titania TiO2 is a polymorphic oxide, inclusive of two common polymorphs: anatase (space group I41/amd, a0=0.37852 nm, c0=0.95139 nm) and rutile (space group P42/mnm, a0=0.45933 nm, c0=0.29592 nm) , both with octahedrally coordinated tetragonal structures. Anatase is a metastable structure and readily transforms to the stable morphic rutile upon heating (Gribb & Banfield, 1997). Because of their wide application in ceramics, catalysis, electronics, sensors and electrodes, they…

LATTICE DEFORMATION AND PHASE TRANSFORMATION FROM NANO-SCALE ANATASE TO NANO-SCALE RUTILE TiO2 PREPARED BY A SOL-GEL TECHNIQUE

Nano-scale rutile phase was transformed from nano-scale anatase upon heating, which was prepared by a sol-gel technique. The XRD data corresponding to the anatase and rutile phases were analyzed and the grain sizes of as-derived phases were calculated by Sherrer equation. The lattice parameters of the as-derived anatase and rutile unit cells were calculated and compared with those of standard lattice parameters on PDF cards. It was shown that the smaller the grain sizes, the larger the lattice deformation. The lattice parameter a has the negative deviation from the standard and the lattice parameter c has the positive deviation for both phases. The particles sizes had preferential in-fluence on the longer parameter between the lattice parameters of a and c. With increasing temperatures, the lattice parameters of a and c in both phases approached to the equilibrium state. The larger lattice deformation facilitated the nucleation process, which lowered the transformation temperature. During the transformation from nano-scale anatase to rutile, besides the mechanism involving retention of the {112} pseudo-close-packed planes of oxygen in anatase as the {100} pseudo-close-packed planes in rutile, the new phase occurred by relaxation of lattice deformation and adjustment of the atomic sites in parent phase. The orientation relationships were suggested to be anatase {101}//rutile {101} and anatase <201>//rutile<111>, and the habit plane was anatase (101).