Magnéli-like phases in epitaxial anatase TiO2thin films

Abstract

Using high-resolution transmission electron microscopy and image simulation techniques in combination with ab initio calculations, we show the existence of two different superlattices of crystallographic shear planes, analogous to the Magnéli phases of rutile, in oxygen-deficient films of anatase TiO 2 epitaxially grown on LaAlO 3 substrates. (103)-and (101)-oriented shear plane structures are detected in the outer film region and in proximity of the film/substrate interface, respectively. We show that these shear planes are characterized by TiO-like cubic local structures, which can deviate from the Ti n O 2n−1 stoichiometry of the classical rutile-derived Magnéli phases, particularly in the outer part of the film. Computed formation energies provide insights into the thermodynamic stability of the observed structures and their relations to the growth dynamics.

Formation and stability of reduced TiOx layers on anatase TiO2(101) : Id

“…Similarly, based on the Ti 3+ /Ti 4+ ratio of Ti ions, another study determined the black shell of anatase TiO 2 nanotubes to be amorphous Ti 4 O 7 [7]. Strips of CSPs have been reported also in anatase TiO 2 (001) thin films epitaxially grown on LaAlO 3 [14], where they have been attributed to anatase-derived Magnéli-like phases Ti n O 2n−1 (n=5,6,7).…”

Poetics of Interplay and Interferences of Potentiodynamic Sweeps and Peaks in Electrocatalysis for Oxygen Electrode Reactions

“…In such a respect, the mine decisive step towards spontaneous latent storage and rather fast spillover widespreading phenomena of the Pt−OH(Au−OH) is the consequence of a strong first principle thermodynamic confirmed evidence (Density Functional Calculations, DFC) by Vittadini et al, [12,13] that water molecules undergo prevailing spontaneous dissociative adsorption on anatase (101), and even rutile titania, and more so on the higher altervalent hypo-d-oxides [4][5][6][7][8]13,14] of tungsten bronze type, molybdenum, tantalum, niobium, yttrium and/or cerium, etc., as the general oxophilicity properties of hypo-d-metal oxides. In addition, the simultaneous first-principles molecular-dynamic showed the existence of a mechanism for thermodynamically favored spontaneous dissociative adsorption of water molecules even at low coverage of oxygen vacancies [39] of the anatase (101) surface, [12,13] and consequently even more so at the MPs, [16,17] as substantially suboxide structure significant both as highly bulk electronic conductive matrix (up to and even more than 1,000 S/cm), [17] perfect membrane type surface and bulk matrix transferring hydroxide and other ionic species, [18−20] and the interactive (SMSI) [10] hypo-d-oxide type catalyst support.…”

“…In addition, the simultaneous first-principles molecular-dynamic showed the existence of a mechanism for thermodynamically favored spontaneous dissociative adsorption of water molecules even at low coverage of oxygen vacancies [39] of the anatase (101) surface, [12,13] and consequently even more so at the MPs, [16,17] as substantially suboxide structure significant both as highly bulk electronic conductive matrix (up to and even more than 1,000 S/cm), [17] perfect membrane type surface and bulk matrix transferring hydroxide and other ionic species, [18−20] and the interactive (SMSI) [10] hypo-d-oxide type catalyst support. Actually, it has for longer been known that TiO2 can easily accommodate suboxide type of oxygen vacances and deficiances, and in broader sense a wide range of various substoichiometries, [13,14] along with reducing defects in TiO2. MPs then can be described as resulting from a regular arrangement of crystallographic shear (CSh) planes in oxygen-deficient rutile structure, the latter being stable for intermediate (MPs hybrid) stoichiometries between Ti2O3 and TiO2, as two interfering states of the MPs steucture.…”

“…In addition, the simultaneous first-principles molecular-dynamic showed the existence of a mechanism for thermodynamically favored spontaneous dissociation of water molecules even at low coverage of oxygen vacancies of the anatase (101) surface, [13] and consequently even more so at the Magneli phases (MPs), [14,15] as substantially suboxide structure significant both as highly electronic conductive (up to and even more than 1,000 S/cm), perfect membrane type surface and bulk network transferring hydroxide specie, and ideal interactive hypo-doxide type catalyst support. [16,17] In fact, this is the status of reversible open circuit spontaneous dissociative adsorption of water molecules at the equilibrium state, something like capillary phenomena in adsorption after some critical coverage extents.…”

Understanding Phonon Interactions with Defects in Functional Oxide Materials

“…The most common characterization method for the identification of the presence of Magn'eli phases is by diffraction imaging [182,186,187,190,[194][195][196][197][198][199][200]. In polycrystalline samples, X-ray diffraction has been used to identify the formation of of new Magnélie phases in TiO 2 [190,[198][199][200].…”