Details about defect formation on doping of ATLS by aliovalent dopants
can be found in [36].
FromFig. 3, it can be concluded that the surface is catalytically active
regarding the oxygen incorporation reaction. It is obvious that the
oxygen concentration near the surface is even for the undoped sample
LSO sufficiently high (near 10%) under the conditions chosen.
In Fig. 5, the surface exchange coefficients are plotted against the inverse
temperature. All samples exhibit a typical Arrhenius behaviour
meaning that the surface incorporation reaction is thermally activated.
Obviously doping with Al, Mg and Fe increases the incorporation rate
of oxygen into the ATLS. Except for the iron doping where the results
are not clear, the other two doping elements increase the exchange
rate by one order of magnitude.
The doped samples exhibit higher surface concentrations as well
as higher surface exchange coefficients as compared to the undoped
sample. This indicates that doping has a direct influence to the oxygen
incorporation reaction most probably due to allocation of electrons by
transition metals to the oxygen dissociation step. Additionally, the increased
favourability of the interstitial sites (ability of the dopants to potentially
increase the coordination sphere above four) could contribute
to a higher incorporation rate as well.
Because the iron-doped sample does not show clearly higher surface
exchange coefficients than the other doped samples, it can be concluded
that iron cannot be reduced and thus provide electrons under the oxidative
conditions of the diffusion experiments. Electrons can neither be
provided by the ATLS which is a pure ionic conductor.
A comparison of the diffusion depths in Fig. 3a and b shows that the
diffusion in the undoped material is much slower than in the doped
samples. The diffusion depth in LSO is up to ten times less than in the
doped ATLS.
This is of course reflected in the self-diffusivities presented in
Table 3. The diffusivities of the doped materials are one to two orders
of magnitude higher than in the undoped material.
The reason for the higher diffusivities in the doped samples lies on
the increased displacement of the oxygen ions into the channels along
the c-axis where they can move interstitially. The trend found in this
study is LSO «LFSO b LASO ≤ LMSO.
Details about defect formation on doping of ATLS by aliovalent dopantscan be found in [36].FromFig. 3, it can be concluded that the surface is catalytically activeregarding the oxygen incorporation reaction. It is obvious that theoxygen concentration near the surface is even for the undoped sampleLSO sufficiently high (near 10%) under the conditions chosen.In Fig. 5, the surface exchange coefficients are plotted against the inversetemperature. All samples exhibit a typical Arrhenius behaviourmeaning that the surface incorporation reaction is thermally activated.Obviously doping with Al, Mg and Fe increases the incorporation rateof oxygen into the ATLS. Except for the iron doping where the resultsare not clear, the other two doping elements increase the exchangerate by one order of magnitude.The doped samples exhibit higher surface concentrations as wellas higher surface exchange coefficients as compared to the undopedsample. This indicates that doping has a direct influence to the oxygenincorporation reaction most probably due to allocation of electrons bytransition metals to the oxygen dissociation step. Additionally, the increasedfavourability of the interstitial sites (ability of the dopants to potentiallyincrease the coordination sphere above four) could contributeto a higher incorporation rate as well.Because the iron-doped sample does not show clearly higher surfaceexchange coefficients than the other doped samples, it can be concludedthat iron cannot be reduced and thus provide electrons under the oxidativeconditions of the diffusion experiments. Electrons can neither beprovided by the ATLS which is a pure ionic conductor.A comparison of the diffusion depths in Fig. 3a and b shows that thediffusion in the undoped material is much slower than in the dopedsamples. The diffusion depth in LSO is up to ten times less than in thedoped ATLS.This is of course reflected in the self-diffusivities presented inTable 3. The diffusivities of the doped materials are one to two ordersof magnitude higher than in the undoped material.The reason for the higher diffusivities in the doped samples lies onthe increased displacement of the oxygen ions into the channels alongthe c-axis where they can move interstitially. The trend found in thisstudy is LSO «LFSO b LASO ≤ LMSO.
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