NDLI: Self-diffusion in α-Fe$_{2}$O$_{3}$ natural single crystals

Content Provider	Springer Nature Link
Author	Amami, B. Addou, M. Millot, F. Sabioni, A. Monty, C.
Copyright Year	1999
Abstract	Measurements of$^{18}$O self-diffusion in hematite (Fe$_{2}$O$_{3}$) natural single crystals have been carried out as a function of temperature at constant partial pressure a$_{O}$ $_{2}$=6.5·10$^{−2}$ in the temperature range 890 to 1227 °C. The a$_{O}$ $_{2}$ dependence of the oxygen self-diffusion coefficient at fixed temperature T=1150 °C has also been deduced in the a$_{O}$ $_{2}$ range 4.5·10$^{−4}$ - 6.5·10$^{−1}$. The concentration profiles were established by secondary-ion mass spectrometry; several profiles exhibit curvatures or long tails; volume diffusion coefficients were computed from the first part of the profiles using a solution taking into account the evaporation and the exchange at the surface. The results are well described by $$D_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. -} s}} \right) = 2.7 \cdot 10^8 a_{O_2 }^{ - 0.26} \exp \left( { - \frac{{542\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. -} {mol}}} \right)}}{{RT}}} \right)$$ From fitting a grain boundary diffusion solution to the profile tails, the oxygen self-diffusion coefficient in sub-boundaries has been deduced. They are well described by $$D''_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. -} s}} \right) = 3.2 \cdot 10^{25} a_{O_2 }^{ - 0.4} \exp \left( { - \frac{{911\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. -} {mol}}} \right)}}{{RT}}} \right)$$ Experiments performed introducing simultaneously$^{18}$O and$^{57}$Fe provided comparative values of the self-diffusion coefficients in volume: iron is slower than oxygen in this system showing that the concentrations of atomic point defects in the iron sublattice are lower than the concentrations of atomic point defects in the oxygen sublattice. The iron self-diffusion values obtained at T>940 °C can be described by $$D_{Fe} \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. -} s}} \right) = 9.2 \cdot 10^{10} a_{O_2 }^{ - 0.56} \exp \left( { - \frac{{578\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. -} {mol}}} \right)}}{{RT}}} \right)$$ The exponent - 1/4 observed for the oxygen activity dependence of the oxygen self-diffusion in the bulk has been interpreted considering that singly charged oxygen vacancies V O • are involved in the oxygen diffusion mechanism. Oxygen activity dependence of iron self-diffusion is not known accurately but the best agreement with the point defect population model is obtained considering that iron self-diffusion occurs both via neutral interstitals Fe x i and charged ones.
Starting Page	358
Ending Page	370
Page Count	13
File Format	PDF
ISSN	09477047
Journal	Ionics
Volume Number	5
Issue Number	5-6
e-ISSN	18620760
Language	English
Publisher	Springer-Verlag
Publisher Date	1999-01-01
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Biomedicine general Analytical Chemistry Physical Chemistry Electrochemistry Optical and Electronic Materials
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Engineering Materials Science Chemical Engineering

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