Nonlinear size dependence of anatase TiO2 lattice parameters

We characterized the size dependence of anatase TiO2 lattice parameters using Rietveld analysis of angle-dispersive synchrotron x-ray diffraction data obtained on a suite of nanocrystalline samples. The refined crystal structure and microstructure data suggest that for crystallites with size less than ∼10nm, the lattice parameters vary nonlinearly. Small lattice expansion, associated with possible increased Ti vacancy and lattice strain, at reduced crystallite size observed in our samples is in contrast to the lattice contraction behavior reported for “pure” anatase nanocrystals. The nonlinear, composition-dependent variation of anatase unit cell volume contrasts with the linear expansion behavior of rutile lattice at finite sizes.