Variations in the local structure of nano-sized anatase TiO2

The structures of three polymorphs of TiO2 (anatase, rutile & brookite) are examined using neutron diffraction and total scattering. While the short-range structures of (bulk) rutile and brookite show excellent agreement with their average crystal structures, the structure of the anatase samples changes with reduction of particle size. Reverse Monte Carlo (RMC) analysis reveals that a fraction of oxygen atoms in the anatase nanoparticles are displaced away from their ideal positions. The displacement results in a change to the octahedral geometry which is compared with a theoretical structural modification that results in a reduced band gap.