Structural investigations of organometallic catalysts, catalyst precursors and ligands

Abstract

It is well known that, on reduction, TiO forms extended planar defects, known as Crystallographi~ Shear (CS) Planes, ~~at accommodate the non-stoichiometrv. Further, these CS Planes interact over large distances (~lOOA or more) to form regular, or nearly regular arrays in an otherwise perfect crystal. It has been shown, by theoretical computer based atomistic :simulation studies that extensive structural relaxation :around the CS Plane is responsible for its stability ,over point defect formation, even in composition regions ,very close to stoichiometry. 'In this paper, we will elaborate on these earlier findings, and show how our computer simulation studies correctly predict, firstly, the formation of the Magnetic phases, Ti 0 2 _ 4<n<9 in regions far from stoichiometry and, sec~naly, the coexistence of both cs Planes oriented on (121) and (132) rutile lattice planes. The formation of CS Planes from point defects, the mechanism of which must deoend on the nature of the intrinsic disorder in rutiie Ti0 2 is still a subject which is under close study, since there is no consensus as to the nature of the intrinsic disorder. Both Schottky and anion Frenkel disorder have been proposed and there exists experimental data to back each claim. We will comment on this point using calculated defect formation energies to discuss the nature of the intrinsic disorder predicted from our theoretical model. We will also consider the energetics of some more complex defect species, such as those postulated by Bursill and co-workers, in an attempt to bridge the gap between the two schools of thought concerning intrinsic disorder.