Diffusion of titanium in slightly reduced rutile

Nanocarving of Titania as a Diffusion‐Driven Morphological Instability

“…Consequently, the self diffusivity of Ti increases with decreasing oxygen activity as D Ti / P À1=5 O 2 , which has also been experimentally observed by Akse and Whitehurst, [13] and by Hoshino et al, [14] respectively. By extrapolating the reported diffusivity parallel to the c-axis of rutile in air atmosphere, D Ti =cm 2 s À1 ¼ 0:03  expðÀ238:6 kJ=RTÞ, [13] to the temperature of the present experiments and using D Ti / P À1=5 O 2 , we evaluate D Ti at logðP 0 O 2 =10 5 PaÞ ¼ À23:21 as D Ti =cm 2 s À1 ¼ 1:5  10 À10 . With this numerical value for D Ti and with t el % 1, the advancement of reducing reaction front at x a and x b and hence, the amplitude of a morphological perturbation 2(z b À z a ) were calculated as a function of time.…”

Gas-phase driven nano-machined TiO2 ceramics

“…The proposed oxygen anion diffusion during H 2 reduction of TiO 2 , however, conflicts with results showing that Ti cation diffusion is orders of magnitude faster than that of O anion diffusion [25,26]. This supports diffusion of Ti cations from the surface to the bulk during the H 2 reaction with TiO 2 .…”

Pb diffusion in rutile

“…Diusivities are quite similar for times ranging over nearly an order of magnitude dius such as Ba (Nakayama and Sasaki 1963) whose dimensions likely preclude transport in this manner. Trivalent (e.g., Cr, Sc) and more highly charged cations (e.g., Zr) diuse via an interstitialcy mechanism involving tetravalent interstitial Ti ions (Sasaki et al 1985), as the diusion rates for these cations (as well as that of Ti selfdiusion; e.g., Akse and Whitehurst 1978) depend upon oxygen fugacity such that D G (pO 2 ) )1/5 , which indicates that the controlling point defects are most likely tetravalent Ti interstitials (i.e., Ti i .... ). However, these investigations of tracer diusion in rutile (Sasaki et al 1985), as well as those of Ti self-diusion , also suggest that trivalent Ti interstitials (i.e., Ti i ... ) may become an important defect at lower pO 2 .…”

“…The ionic radius of Pb would likely discourage its interstitial movement, so it may travel via cation vacancies, with charge balance achieved through Ti interstitials and/or oxygen vacancies. Transport via a cation vacancy process would probably result in cation diusivities slower than Ti self-diusion (Sasaki et al 1985), which is true in the case of Pb, although activation energies for diusion of Pb and Ti are similar (250 12 kJ mol )1 for Pb vs. 257 12 kJ mol )1 for Ti; Venkatu and Poteat 1969;Akse and Whitehurst 1978). Diusion governed by a cation vacancy process would also result in an increase in D with increasing pO 2 , rather than the inverse found when an interstitialcy mechanism is dominant [i.e., D G (pO 2 ) )1/5 ].…”