Electrical Properties and Defect Chemistry of TiO₂ Single Crystal. IV. Prolonged Oxidation Kinetics and Chemical Diffusion

Abstract

Measurements of both electrical conductivity and thermoelectric power were used to monitor the equilibration kinetics of undoped single-crystal TiO(2) during prolonged oxidation at 1123 and 1323 K and p(O(2)) = 75 kPa. Two kinetics regimes were revealed: kinetics regime I (rapid kinetics), which is rate-controlled by the transport of oxygen vacancies, and kinetics regime II (slow kinetics), which is rate-controlled by the transport of titanium vacancies. The incorporation of titanium vacancies allows undoped p-type TiO(2) to be processed in a controlled manner. The kinetics data were used to determine the chemical diffusion coefficient (D(chem)) associated with the transport of titanium vacancies, which is equal to D(chem) = 8.9 x 10(-14) m(2) s(-1) and D(chem) = 9.3 x 10(-15) m(2) s(-1) at 1323 and 1123 K, respectively.

Hydrogen generation at irradiated oxide semiconductor–solution interfaces

“…Studies of the electrical properties and defect chemistry continue to appear for this material in both single crystal [219][220][221][222] and nanostructured form [223]. Yet this material to date has not yielded systems for evolving H 2 and O 2 at the 10% benchmark efficiency level.…”

Effect of cooling on electrical conductivity of TiO2

“…Then TiO 2 may be better represented by the formula TiO 2+x or, more precisely Ti 1-x O 2-y , where ( 2). x y > / It was shown that the properties of the p-type TiO 2 are determined by titanium vacancies, which are formed during the prolonged oxidation [28].…”

“…It has been shown that while the equilibria (1)-(3) may be established relatively fast, the formation of titanium vacancies, represented by equilibrium (4), is extremely slow [28]. Therefore, the required concentration of defects may be manipulated not only by oxygen activity during processing, but also by the kinetic factor (equilibration time).…”

“…Therefore, the required concentration of defects may be manipulated not only by oxygen activity during processing, but also by the kinetic factor (equilibration time). Due to the reasons explained above, titanium vacancies may be considered as immobile and, therefore, their concentration in the bulk phase remains practically quenched [28]. Consequently, the concentration of titanium vacancies in Eqs.…”

“…At this stage the following points should be made: 1. The real TiO 2 systems exhibit a concentration gradient of titanium vacancies within a near-surface layer [28]. Therefore, the validity of the defect disorder models outlined above is limited to the bulk phase.…”