I.—Mandeliminohydrin

Review of the anatase to rutile phase transformation

“…It is perceived widely that the most important factor affecting the phase transformation is the presence and amount of defects on the oxygen sublattice, viz., TiO 2-x [67,157,162,163]. Ease of rearrangement and transformation are enhanced by relaxation (lessening of structural rigidity) of the large oxygen sublattice through the increased presence of oxygen vacancies [109,164,165]. This effect has been shown through firing in different atmospheres, where neutral or reducing conditions of low oxygen partial pressure generally greatly enhance the anatase to rutile transformation [3,67,166], although contrary effects have been reported as vacuum conditions have been observed to slow the phase transformation [109].…”

“…It has been suggested that cations of small radii and low valence accelerate the transition to rutile owing to the increase in oxygen vacancies that result from the assumed substitution of Ti 4? ions with cations of lower valences [43,109,157,164,165]. Charge neutrality thus requires an increase in the level of oxygen vacancies and/or the formation of Ti interstitials of lower valence [82,172].…”

“…An important issue to consider is that certain cationic dopants may exhibit more than one valence and the associated potential for reduction-oxidation reactions [165,169]. These can result in an increase in the level of oxygen vacancies (promotion of the phase transformation through increase in lattice relaxation) and/or the formation of Ti 3? interstitial (inhibition of the phase transformation through lattice constraint).…”

“…c MnO 2 -doped titania fired in air at 945°C [164]. d Undoped titania fired in air at 945°C [164] If the solubility limit for impurities or dopants is exceeded, then their precipitation can facilitate the phase transformation through heterogeneous nucleation [67,171].…”

The critical size mechanism for the anatase to rutile transformation in TiO2 and doped-TiO2

“…1 The phase transition is non-reversible because of the greater thermodynamic stability of the rutile phase. 2 The ART is kinetically defined and the reaction rate determined by parameters such as particle shape/size, 3 purity, 3,4 source effects, 5 atmosphere 6 and reaction conditions. 7 It seems clear that the mechanism for phase transformation is one of nucleation and growth.…”