Prediction of electronic, structural and elastic properties of the hardest oxide: TiO₂

Abstract

This work combines the theory of elasticity with first principles quantum mechanic calculations to predict the electronic, structural and elastic properties: elastic constants, bulk moduli of the TiO2 (Titania) in the Pnma phase. Band‐structure shows a direct gap in Γ which increases its value under hydrostatic pressure. It has two regimes: in the range 0–50 GPa the band‐gap has a negative second pressure derivative and changes its sign in the range 50–100 GPa. The band gap becomes indirect at pressures above 150 GPa. This phase improves its mechanical stability and insulator properties under extreme conditions of hydrostatic pressures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase transitions and mechanical stability of TiO2 polymorphs under high pressure

“…A high-pressure phase of TiO 2 with an a-PbO 2 -type was found in garnet of diamondiferous quartzofeldspathic rocks [31], namely columbite TiO 2 , whose dielectric properties and lattice dynamics were reported, indicating the role of the B 1u and B 3u modes in pressure-induced phase transition from columbite to baddeleyite TiO 2 [58]. Dubrovinsky et al [35] have synthesized the nine-coordinated to O in the cotunnite-type TiO 2 at pressures above 60 GPa and temperatures above 1000 K, which was one of the least compressible and hardest oxides [36]. Its structural, elastic, mechanical and electronic properties have been studied [36][37][38], which proved its high hardness due to the high valence electron density, short bond lengths and unusual mixtures of ionic and covalent bonds [37].…”

“…4h [17,18], brookite OI; Pbca; D 15 2h [19,20], bronze (TiO 2 (B), C2/m, C 3 2h ) [21][22][23][24][25][26][27], hollandite (TiO 2 (H), I4/m, C 5 4h ) [28,29] and ramsdellite (TiO 2 (R), Pbnm, D 16 2h ) [30], the high pressure phases columbite (a-PbO 2 -type, TiO 2 -II, Pbcn, D 14 2h ) [31,32], baddeleyite (MI, P2 1 /c, C 5 2h ) [33,34], cotunnite (OII, Pnma, D 16 2h ) [35][36][37][38] [44] and hexagonal Fe 2 P-type (P 62m; D 3 3h ) [45]. Recently, cubic phase TiO 2 has been widely studied due to its potential applications.…”

Hydrophilic and optical properties of nanostructured titania prepared by sol–gel dip coating

“…lower than the theoretical value of anatase titania (4.26 g/cm 3 ). The reduced mass density of the coatings can be explained by considering a film porosity that is very much pronounced in samples prepared by using Sol-2.…”

“…Moreover, the values of the contact angles suggest that titania hydrophilic properties are influenced both by interfacial tensions according to Young´s equation and other phenomena, such as substrate surface roughness, porosity, and grain size dimension. In fact, from Table 2 Moreover, because the UV-induced photocatalytic properties of TiO 2 are associated with film hydrophilicity [3,16], one can deduce that photocatalytic activity is favored in samples grown from Sol-2-like precursor solutions.…”

“…TiO 2 -based films or powders are of great interest for optical, catalytic, photocatalytic and photovoltaic applications because of their electronic and optoelectronic properties and their high chemical, biological and structural stability [1][2][3][4][5][6][7][8][9][10]. In particular, the possibility of controlling the solar energy absorption, the photocatalytic activity and the surface hydrophilic performances of TiO 2 coatings by tailoring their surface morphology, crystalline structure and the energy gap is an important aim to achieve, in particular for advanced device applications [2,6,8,[11][12][13].…”