First-principles calculations of the phase stability ofTiO2

Abstract

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.

Air Stable Doping and Intrinsic Mobility Enhancement in Monolayer Molybdenum Disulfide by Amorphous Titanium Suboxide Encapsulation

“…The rutile phase was chosen for the simulation since it is the most common natural form of TiO2. 42 As stated before, to the K point for ML MoS2. This is because using a bigger supercell in the DFT simulations results in the corresponding brillouin zone being smaller and, hence, the K point folds into the Γ point.…”

Structure of a Model Dye/Titania Interface: Geometry of Benzoate on Rutile-TiO2 (110)(1 × 1)

“…The titanium and oxygen ions are described using triple valence all-electron basis sets contracted as 86-411G** and 8-411G**, respectively. These basis sets were developed in previous studies of the bulk and surfaces of titania in which a systematic hierarchy of all-electron basis sets was used to quantify the effects of using a finite basis set 34,35 . The C and H atoms of the benzoate are described using basis sets of a similar quality, namely 6311G* and 821G*, respectively.…”

A review of TiO2 nanoparticles

“…Anatase: Anatase TiO 2 also has a tetragonal structure but the distortion of the TiO 6 octahedron is slightly larger for the anatase phase [28,33], as depicted in Figure 1. Muscat et al [37] found that the anatase phase is more stable than the rutile at 0 K, but the energy difference between these two phases is small (∼2 to 10 kJ/mol). The anatase structure is preferred over other polymorphs for solar cell applications because of its higher electron mobility, low dielectric constant and lower density [23].…”