Correlation between crystallite sizxes and microstrains in TiO_2 nanopowders

摘要

Nanopowders of TiO_2 doped with by V, Nb, Ta were obtained by laser-induced pyrolysis. The profiles of the diffraction peaks were Fourier analysed with a single-peak method and the microtructural parameters (average crysallite size) and <ε~2>~1/2 (mean-square root microstrain) were estimated. A linear correlation between <ε~2>~1/2 and 1/ was observed in both aatase and rutile phases. For a given crystallite size, the microstrains as well as the dispersion of data were larger in anatase then in rutile. Indeed, one of the factos inducing the anatase-to-rutile transformation may be the presence of larer microstrains in anatase. In rutile, the high correlation found between <ε~2>~1/2 and 1/ suggests tat in this phade the microsrains present in the structre are due only to the geometricla constraints of the suface. Indeed, for infinite crystallite size no microstrains are expected. In anatase, microsrains depend also on the specific cation present in the crsytallite.