Reduction of the TiO_2–x melting temperature induced by oxygen deficiency with implications on experimental data accuracy and structural transition processes

Abstract

1 Introduction Transition metal oxides, such as TiO 2 are known to release oxygen upon heating [1][2][3][4]. This thermal self-reduction effect is of great importance to a multitude of applications, such as the manufacture of oxide electronics devices, heterogeneous catalysis, ultra high performance mechanical parts and possibly the memristive effect. In TiO 2 , the thermal self-reduction effect is employed to achieve n-type doping for semiconductor and transparent conductor applications [2 -5]. Titania, alone or in combination with metal nanoparticles, is being investigated as a catalyst for sustainable energy applications, especially water oxidation and CO 2 reduction. At the same time, Ti alloys are widely used as a structural material under conditions of high mechanical stress at high temperatures, such as gas turbine blades [6,7], and titania based ceramics are employed in high temperature applications. It was recently

In situ FT-IR study on the homogeneous nucleation of nanoparticles of titanium oxides from highly supersaturated vapor

“…<1200 K for 2 nm anatase spheres. 42 The reduction in the melting temperature due to size effects and oxygen deficiency promotes the formation of liquid droplets in the initial stages of nucleation. Rapid crystallization at a relatively low temperature and the decrease in the melting temperature of oxygen-deficient titanium oxides suggest that the noncrystalline particles are droplets of molten liquid.…”

Structure of molten titanium dioxide

“…These phenomena are all related to charged defect formation in TiO 2 , and/or to the formation of Ti n O 2n-1 Magnéli phases. Knaup et al [10] have recently raised the possibility of a liquid intermediate phase in both memristive device operation and during flash sintering, presumably in the form of local melting. Narayan [4] has proposed a mechanism for flash sintering which does indeed involve local melting at grain boundaries.…”

How the aggregation of oxygen vacancies in rutile-basedTiO2−δphases causes memristive behavior

“…However, this earlier study was limited to a small number of examined vacancy arrangements by the prohibitive computational cost of ab-initio methods that can describe the electronic structure of V O in TiO 2 16 . Still, combined with the finding that rutile is severely destabilized by oxygen deficiency, as evidenced by a pronounced reduction in melting temperature 17 , these results lead to an important question for the understanding of the memristive effect in transition metal oxides in general: Is the observed formation of Magnéli phases prerequisite for the effect or is the resistance change caused by a larger class of structural features, with the Magnéli phase being the thermodynamically most favorable structure exhibiting these features?…”