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Argirusis C.,National Technical University of Athens | Argirusis C.,Energy Research Center Niedersachsen | Jothinathan E.,Catholic University of Leuven | Sourkouni G.,Energy Research Center Niedersachsen | And 3 more authors.
Solid State Ionics

Dense apatite type lanthanum silicate LSO (La9.33Si 6O26) electrolyte and the Al-, Fe- and Mg-doped compositions LASO (La9.83Al1.5Si4.5O 26), LFSO (La9.83Fe1.5Si4.5O 26), and LMSO (La9.93Mg0.9Si 5.1O26) have been prepared and investigated in this work in terms of their oxygen self-diffusion and total conductivity. Oxygen self-diffusivities and surface exchange coefficients and the respective activation enthalpies have been estimated and discussed. All samples exhibit a typical Arrhenius behaviour of the surface exchange coefficients meaning that the surface incorporation reaction is thermally activated. 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. It has been found that doping enhances the self-diffusion in all cases as compared to the undoped material. The trend found in this study is LSO LFSO < LASO ≤ LMSO. The diffusivities of the apatite type lanthanum silicate (ATLS) electrolyte materials are higher compared to yttria stabilized zirconia which is the state-of-the-art electrolyte material. The activation enthalpy for oxygen diffusion in YSZ is higher as compared to the ATLS used in this study. Conductivity studies were also made on samples of the same composition and density. We observed that aluminium- and magnesium-doped samples have better conductivity than the undoped counterpart. The role of iron on the conduction mechanism is unclear, but it shows a positive influence on the conductivity. This behaviour is in agreement with conductivity measurement results in the literature, where it has been found that doping with aluminium and magnesium leads to an increased ionic conductivity.© 2014 Published by Elsevier B.V. Source

Sadykov V.,Novosibirsk State University | Sadovskaya E.,Novosibirsk State University | Bobin A.,RAS Boreskov Institute of Catalysis | Kharlamova T.,Tomsk State University | And 5 more authors.
Solid State Ionics

For powders of oxide-ion conductors based on Al/Fe- doped lanthanum silicates as well as Sc+Ce-doped zirconia, the temperature -programmed exchange with C18O2 in the SSITKA mode was applied for estimation of the oxygen self-diffusion coefficients Do. Comparison with results obtained for dense ceramics of these electrolytes using SIMS isotope profiling and conductivity measurements demonstrated a reasonable agreement for powders sintered at high temperatures, thus providing required verification of C18O2 SSITKA approach. For powders calcined at moderate temperatures much lower values of DO were obtained thus suggesting a strong negative effect of inhomogeneity of dopants spatial distribution on the oxygen mobility. ©2014 Elsevier B.V. All rights reserved. Source

Argirusis C.,National Technical University of Athens | Antonaropoulos G.,National Technical University of Athens | Sourkouni G.,Energy Research Center Niedersachsen | Sourkouni G.,Clausthal University of Technology | Jomard F.,University of Versailles
Solid State Ionics

Low resistance of C/C-SiC composites against oxidation at high temperatures created the need to develop materials that could be used as oxygen protective layers. Yttrium silicate (Y2SiO5) has been proposed as an excellent candidate for this purpose. In order to investigate whether Y 2SiO5 is a sufficient barrier against oxygen, the transport parameters of oxygen in this material should be determined. In the present study, 18O2 tracer diffusion experiments have been conducted in the temperature range between 1000 °C and 1300 °C. Secondary ion mass spectrometry (SIMS) was used to determine tracer diffusivities D* and oxygen incorporation rates k * in undoped and in 0.3 at.% praseodymium doped yttrium silicate. Activation enthalpies EA(D*) and E A(k*) were determined. An indication of anisotropic oxygen diffusion in yttrium silicate has been found. © 2014 Elsevier B.V. Source

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