Transformation Enthalpies of the TiO<sub>2</sub> Polymorphs

Mitsuhashi, T.; Kleppa, O. J.

doi:10.1111/j.1151-2916.1979.tb19077.x

Cited by 110 publications

(80 citation statements)

References 8 publications

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“…7), rutile is more stable than anatase. This has been confirmed by thermodynamic studies [5,9,76,148,152], which show that negative pressures would be required for anatase to be more stable than rutile [2]. The transformation to rutile thus is irreversible.…”

Section: Stability Of the Tio 2 Phasessupporting

confidence: 58%

“…Since rutile is the equilibrium phase [2,7,9,20,76,113,148,152], the presence of anatase demonstrates that these studies cannot represent equilibrium conditions, which normally employ phase diagrams for illustration. Dachille et al [154] reported what was considered to be an pressure-temperature diagram approximating equilibrium for TiO 2 , which is shown in Fig.…”

Section: Stability Of the Tio 2 Phasesmentioning

confidence: 99%

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Review of the anatase to rutile phase transformation

2010

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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.

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Section: Stability Of the Tio 2 Phasessupporting

confidence: 58%

Section: Stability Of the Tio 2 Phasesmentioning

confidence: 99%

Review of the anatase to rutile phase transformation

2010

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“…Abbreviations defined in Table 1. for the system MgO-CO2-H20 Hemingway and Robie, 1973) clearly show the stable phase assemblage to be brucite + magnesite + H20(1) rather than hydromagnesite, nesquehonite, or artinite, yet the latter minerals are widespread and the former assemblage is unknown in surface rocks so far as we can ascertain. Similarly, anatase is a TiO: polymorph commonly found in diagenetic, hydrothermal, and altered rocks, yet it is clearly metastable relative to rutile (Jamieson and Olinger, 1969;Mitsuhashi and Kleppa, 1979;Robinson et al, 1982). In addition, Jiang et al (1990) presented evidence that illite (and smectite) are metastable relative to micas + pyrophyllite for all geological conditions.…”

Section: Metastability Of Boehmite Gibbsite Bayerite and Nordstranmentioning

confidence: 99%

Metastability in Near-Surface Rocks of Minerals in The System Al₂O₃-SiO₂-H₂O

Anovitz

Perkins

Essene

1991

Clays and clay miner.

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--Gibbs free energies for phases in the system m1203-SiO2-H20 have been calculated from reversed experiments in order to correct earlier values and to calculate a phase diagram consistent with more recent experiments. An internally consistent diagram could not be calculated that agreed with all published experiments, and choices of preferred data were made. The following Gibbs free energies, relative to the elements at STP ( The above values were calculated assuming literature values for corundum, quartz, and H20 (v). Examination of available thermodynamic, experimental, and observational data on the aluminum hydroxides gibbsite, boehmite, bayerite, and nordstrandite suggests that these minerals are metastable with respect to diaspore + water at STP and at higher temperatures. Similarly, halloysite and dickite are metastable with respect to kaolinite at these conditions. The occurrence of these minerals in soils must therefore be ascribed to nonequilibrium processes, and the use of equilibrium phase diagrams to explain their occurrence is inappropriate.

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“…[6][7][8][9][10] However, the enthalpy change of the anatase to rutile transformation remains somewhat controversial, with room-temperature experiments yielding values ranging from ⌬H 298 ϭϪ11.7 kJ/mol ͑Ref. 7͒ to ϩ0.42 kJ/mol ͑Ref.…”

Section: Introductionmentioning

confidence: 99%

First-principles calculations of the phase stability ofTiO2

2002

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First-principles calculations of the crystal structures, bulk moduli, and relative stabilities of seven known and hypothetical TiO 2 polymorphs ͑anatase, rutile, columbite, baddeleyite, cotunnite, pyrite, and fluorite structures͒ have been carried out with the all-electron linear combination of atomic orbitals ͑LCAO͒ and pseudopotential planewave ͑PW͒ methods. The anatase versus rutile relative phase stability at 0 K and zero pressure has been investigated using high-quality basis sets and carefully controlled computational parameters. From the optimal crystal structures obtained with the Hartree-Fock theory at various pressures, the bulk modulus and phase transition pressures of various high-pressure polymorphs have been derived at the athermal limit. In most cases, the calculated unit cell data agree to within 2% of the corresponding experimental determination. Complete predicted structural data ͑unit cell constants and fractional atomic coordinates͒ are presented for the baddeleyite and pyrite forms. The calculated bulk moduli are within 10% of the most reliable experimental results. Both the all-electron LCAO and pseudopotential PW methods predict anatase to be more stable than rutile at 0 K and ambient pressure. The computed anatase-columbite, rutile-columbite, columbite-baddeleyite, and baddeleyite-cotunnite phase transitions appear in the same order as observed in experiments, and the transition pressures agree semiquantitatively with those measured. The pyrite and fluorite structures are predicted to be less stable than other polymorphs at pressures below 70 GPa in agreement with experiments. Finally, the elastic properties, compressibilities and phase transformations of the various polymorphs are discussed in terms of simple models based on the behavior of the constituent Ti-O polyhedra under compression.

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Transformation Enthalpies of the TiO₂ Polymorphs

Cited by 110 publications

References 8 publications

Review of the anatase to rutile phase transformation

Review of the anatase to rutile phase transformation

Metastability in Near-Surface Rocks of Minerals in The System Al₂O₃-SiO₂-H₂O

First-principles calculations of the phase stability ofTiO2

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Transformation Enthalpies of the TiO2 Polymorphs

Cited by 110 publications

References 8 publications

Review of the anatase to rutile phase transformation

Review of the anatase to rutile phase transformation

Metastability in Near-Surface Rocks of Minerals in The System Al2O3-SiO2-H2O

First-principles calculations of the phase stability ofTiO2

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Transformation Enthalpies of the TiO₂ Polymorphs

Metastability in Near-Surface Rocks of Minerals in The System Al₂O₃-SiO₂-H₂O