Titanium dioxide, TiO 2 , is an important photocatalytic material that exists as two main polymorphs, anatase and rutile. The presence of either or both of these phases impacts on the photocatalytic performance of the material. The present work reviews the anatase to rutile phase transformation. The synthesis and properties of anatase and rutile are examined, followed by a discussion of the thermodynamics of the phase transformation and the factors affecting its observation. A comprehensive analysis of the reported effects of dopants on the anatase to rutile phase transformation and the mechanisms by which these effects are brought about is presented in this review, yielding a plot of the cationic radius versus the valence characterised by a distinct boundary between inhibitors and promoters of the phase transformation. Further, the likely effects of dopant elements, including those for which experimental data are unavailable, on the phase transformation are deduced and presented on the basis of this analysis.

The agglomeration, electrokinetic properties and electrophoretic deposition behaviour of aqueous suspensions of ZrO 2 with carboxylic acid additives were studied in comparison with conventional pH adjustment. It was found that citric acid imparted negative zeta-potential values and electrosteric stabilisation to particles in suspensions at all pH levels. The examination of additions of carboxylic acids to ZrO 2 suspensions revealed that these reagents cause a sharp drop in zeta-potential at distinct addition levels, which correspond to surface saturation of the particles with negatively charged carboxylate groups. Adsorption cross sections of citric acid, EDTA and oxalic acid were evaluated from these results, showing that both citric acid and EDTA coordinate to ZrO 2 surfaces by two carboxylate groups while oxalic acid is coordinated by one group. The use of carboxylic acids was shown to facilitate superior electrophoretic deposition in comparison with zeta-potential modification by conventional pH adjustment through improved suspension stability.

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The semiconducting properties of single‐crystal TiO2 and their changes during prolonged oxidation at elevated temperatures and under controlled oxygen activity were monitored using measurements of electrical conductivity and thermo‐electric power. Two kinetic regimes were revealed: Regime I – rapid oxidation, associated with the transport of oxygen vacancies, and Regime II – prolonged oxidation, which corresponds to the transport of titanium vacancies. The present data represent the first documented evidence for the formation and transport of titanium vacancies in TiO2. This finding allows the processing of p‐type TiO2 without the incorporation of aliovalent foreign ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The present work provides a critical review of the science and technological state-of-the-art of defect engineering applied to oxide perovskites in thermocatalytic, electrocatalytic, photocatalytic, and energy-storage applications.

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