Density Functional Theory Calculations of Dense TiO₂ Polymorphs:  Implication for Visible-Light-Responsive Photocatalysts

Abstract

Structural parameters and electronic band gaps of dense TiO(2) polymorphs, i.e., alpha-PbO(2), baddeleyite, fluorite, and cotunnite types of structures, were calculated using a first-principles density functional method with local-density approximation. The ambient phases, i.e., rutile and anatase, with known theoretical and experimental data were used to ensure the validity of the calculations. The fluorite-type TiO(2) turned out to have the narrowest band gap, 1.08 or 2.18 eV after applying a very approximate band gap correction, due to highly symmetrical TiO(8) polyhedra with Ti(3d) and O(2p) orbitals in the most mixed state. Ti with eight coordinated oxygens, as feasible under high pressure or residual stress, may have potential applications as a visible-light-responsive photocatalyst.

Crack tip plasticity in single crystal UO2: Atomistic simulations

“…While under tensile state, recent MD simulations using the same potential found that UO 2 transforms from Fluorite phase to Scrutinyite phase, and the results are validated by DFT calculations [17]. The Rutile phase of UO 2 has never been reported before, even though the coexistence of Rutile and Scrutinyite phases has been observed both in experiments and simulations on TiO 2 [37,38]. Furthermore, DFT calculations show that the Rutile phase TiO 2 transforms into a Fluorite phase under compressive strain [39], indicating a possible reverse process under tensile loading.…”

Nonstoichiometric Titanium Oxides via Pulsed Laser Ablation in Water

“…The synthesis of such a tubular material from atom clusters and their lamellar derivative is analogous to the fabrication of carbon onions via arc discharge in water [11] and Au tubes via PLAL and subsequent dwelling in water [12]. We focused on the nonstoichiometry, shape, coalescence, and dense structure, if any, of the TiO x nanocondensates and the phase behavior upon electron irradiation as of concern to the space charge, the surface/interface energetics in terms of unrelaxed or relaxed state and theoretical band gap of such metastable phases [13,14] for potential optoelectronic applications.…”

Dielectric properties and lattice dynamics ofα-PbO2-type TiO2: The role of soft phonon modes in pressure-induced phase transition to baddel

“…7 The cotunnite-type TiO 2 synthesized at pressure (P ) above 60 GPa and temperature above 1000 K is believed to be the hardest oxide yet discovered. 8 In addition, a density functional theory calculation predicted that the high-pressure modification of TiO 2 could lead to a polymorph which responds to visible light, 9 extending the photocatalyst property of TiO 2 from ultraviolet to visible light.…”