Le. Depero et al., STUDY OF THE ANATASE-RUTILE TRANSFORMATION IN TIO2 POWDERS OBTAINED BY LASER-INDUCED SYNTHESIS, Journal of materials research, 8(10), 1993, pp. 2709-2715
Powder samples of pure anatase were produced using laser-induced pyrol
ysis of titanium alkoxides, and the catalysts were prepared using conv
entional wet impregnation methods. The diffraction patterns were inter
preted in microstructural terms by Fourier analysis of their peak prof
iles. The transition temperature for the anatase-rutile transition in
these catalysts was found between 500-degrees and 550-degrees-C. For t
he reflections of the anatase phase, a decrease of their Bragg (2theta
) positions was observed up to 550-degrees-C when the presence of the
rutile phase becomes important. The response of the anatase structure
to the thermal treatment is anisotropic with the c-axis showing the hi
ghest sensitivity to the observed expansion of the lattice. The rutile
Bragg reflections are sharper than those of the anatase phase. The co
rresponding microstructural parameters indicate that, in all cases, th
e transformation is accompanied by an increase of the crystallites and
/or of the lattice perfection. The evolution of these parameters is in
fluenced by the presence of vanadium. The V-treated surface layer must
be particularly distorted and apparently act as a restraint to perfec
ting by thermal treatments. Only the transition to rutile is capable o
f overcoming that restraint by allowing crystallite growth at the expe
nse of the smaller and distorted anatase crystallites.