Point Defects in 3D and 1D Nanomaterials: The Model Case of Titanium Dioxide

Titanium dioxide is one of the most important oxides for applications in energy and environment, such as solar cells, photocatalysis, lithium-ion batteries. In recent years, new forms of titanium dioxide with unusual structure and/or morphology have been developed, including nanocrystals, nanotubes or nanowires. We have studied in detail the point defect chemistry in nanocrystalline TiO₂ powders and ceramics. There can be a change from predominant Frenkel to Schottky disorder, depending on the experimental conditions, e.g. temperature and oxygen partial pressure.

We have also studied the local environment of various dopants with similar ion radius, but different ion charge (Zn²⁺, Y³⁺, Sn⁴⁺, Zr⁴⁺, Nb⁵⁺) in TiO₂ nanopowders and nanoceramics by Extended X-Ray Absorption Fine Structure (EXAFS) Spectroscopy. Interfacial segregation of acceptors was demonstrated, but donors and isovalent ions do not segregate. An electrostatic "space charge" segregation model is applied, which explains well the observed phenomena.