Local order in titania polymorphs

Crystalline structure local order of titania polymorphs, brookite, anatase and rutile is described with a representative octahedron for each phase. The detailed analysis of the atomic bond lengths forming these octahedra helps to understand the macroscopic properties observed in these materials. In rutile samples with an average crystal size between 9.77(9) and 149(2) nm, these lengths did not depend on the crystal size. This behavior is not necessarily similar for anatase and brookite, which have crystalline structures with lower symmetry. The dependence of anatase on rutile in synthesis conditions suggests that atom bond lengths in this titanium polymorph depend on crystal size. Brookite is stabilized with copper and chloride ions. Anatase open crystalline structure can dissolve cations and anions that stabilize it at high temperatures, or can be used as precursors for preparing titanates at low temperatures. Rutile, which is normally obtained after annealing brookite and anatase at high temperatures, can be synthesized at low temperatures in the presence of platinum or tin ions during synthesis or by using TiCl3 as precursor. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.