Growth of crystals in titania-based amorphous gels

The growth of crystals in titania-based amorphous gels was characterized using X-ray diffraction and high-resolution transmission electron microscopic methods. Anatase, rutile and SnO2 crystals can independently precipitate from amorphous gels at lower annealing temperatures through their low-energy surfaces. In the undoped case, the allotropic transformation of anatase to rutile is dominant to form rutile crystals and undergoes rearrangements of the planes 101¯A and 112¯A to the 11¯0R and 101¯R, respectively, in which there exist some dislocations. In the Sn-doped case, the rutile crystal changes its formation route, that is, it grows depending on SnO2 crystals by coherent relationship between {110}S and {110}R and the semi-coherent relationship between {110}S and {101}R, in the latter of which the dislocation adjustment is necessary to reduce the mismatch of the planes. The Sn-doping improves the transformations of the amorphous to anatase and further to rutile, inhibits their growth and produces the fine crystals.