X-ray diffraction study of thermal properties of titanium dioxide

Temperature dependence of microstructure of titanium dioxide, TiO_2, and the phase transition of anatase (A) to rutile (R) were studied by in situ X-ray powder diffraction. The as-synthesized TiO_2 p.a. showed a gradual transition A→R during the temperature increase from ≈ 1200 K to ≈ 1570 K and during the temperature decrease to ≈ 600 K. High-energy ball –milling at room temperature induced a partial transition A→R. The transition continued during the temperature increase to » 1370 K and during the temperature decrease, and is accompanied by sharpening of diffraction lines. Anisotropy of thermal expansion was noticed for both A and R. In the transition A→R, the nuclei of R are formed either throughout the A crystallites (in the case of as-synthesized TiO_2 p.a.) or mainly in the interior of the A crystallites (in the case of the milled TiO_2 p.a.). These nuclei grow in number and size with a prolonged time of thermal agitation