Equilibration kinetics of TiO₂ single crystal at elevated temperatures

Abstract

The equilibration kinetics of single‐crystal TiO2 were determined in the rapid kinetics regime (within the first 10 h) within narrow ranges of oxygen activities, p(O2), under the conditions of 1198–1323 K and p(O2) = 10–10–105 Pa. The determined chemical diffusion coefficient, Dchem, is observed to exhibit a complex dependence on p(O2). Comparison of Dchem for single‐crystal and polycrystalline TiO2 demonstrates that the grain boundaries have a retarding effect on the transport of defects. The present work represents the first assessment of the effect of nonstoichiometry on well defined Dchem for TiO2 within a wide range of p(O2). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Chemical diffusion in metal oxides. Example of TiO2

“…The results of extensive studies on the equilibration kinetics for high-purity TiO 2 specimens, including both single crystal and polycrystalline specimens, have been recently reported [5,16]. These studies, which addressed [15] and AitYounes et al [14] the procedure requirements outlined in "Postulation of the problem," lead to the following conclusions:…”

“…Critical analysis of the chemical diffusion coefficient determined from the gas/solid kinetics for the metal oxide/ oxygen system indicates that there is a substantial discrepancy between the data reported so far in their absolute values and their temperature dependence for binary metal oxides, such as CoO [29] and TiO 2 [9][10][11][12][13][14][15][16][17]. This observed discrepancy requires the consideration of the following issues:…”

“…The equilibration kinetic data may then be used for the determination of the chemical diffusion coefficient using a Fig. 1 The chemical diffusion coefficient for T i O 2 reported in the literature [9][10][11][12][13][14][15][16][17] solution of the diffusion equation, which is adequate to the specific initial and boundary conditions of the experiment.…”

“…1 [9][10][11][12][13][14][15][16]. In most cases, the D chem data were determined from the equilibration kinetics monitored using the electrical conductivity measurements.…”

“…1, exhibit a substantial discrepancy in their absolute values and the temperature dependence [9][10][11][12][13][14][15][16]. These data will be considered below in terms of the possible impact of the applied experimental conditions on the physical meaning of the diffusion data.…”