Oxygen tracer diffusion

Oxygen Tracer Diffusion Coefficient (D ), Oxygen Surface Exchange Coefficient (Ar) and Oxygen Ionic Conductivity (a, in air) of Doped Lanthanum Cobalt Ferrite-Based Perovskites... 

Fig. 3. Temperature dependence of the oxygen tracer diffusion coefficient in the crystals Lai- SryMnOs-s (y = 0.025-circle). Also shown are this work data for Lax- Sr MnO s (y = 0.075-square) and SIMS data for La0.65Sro.35Mn03- (diamond) [21] and extrapolated Arrhenius diffusivity plot for Lao.9Sr0.xMn03 (lower line) [22].

The electrical conductivity of sapphire in a particular crystallographic direction was found to be 1.25mSm 1 at 1773 K. An independent experiment on the same material at the same temperature determined the oxygen tracer diffusion coefficient to be 0.4nm2s 1, the diffusion occurring by a vacancy mechanism. Do these data favour oxygen ion movement as the dominant charge transport mechanism (Relative atomic masses, A1 = 27 and 0=16 density of sapphire, 3980 kgm-3.)... 

Fig. 8.2 Oxygen tracer diffusivities and oxygen permeabilities through liquid boron oxide, fused silica, and a polycrystalline alumina with a grain size of 5 nm. Tracer diffusivity values for B203 and Si02 were obtained from Refs. 9 and 19, respectively. Tracer diffusivity values for A1203 were obtained from data reported in Ref. 18 using a grain size of 5 /im (Ref. 13). Oxygen permeability constants were obtained using the procedure outlined in the text.2...

Indeed, the experiements appear to be precise and carefully executed. The same may be said of the careful thermodynamic study of Picard and Gerdanian on slightly reduced rutile, where the results obtained are also treated in terms of point defects. Interpretation in terms of CS planes would seem to be at least as realistic an alternative as point defects, and it is a pity that the authors have not attempted such an analysis. Other recent papers on the physical and chemical properties of reduced rutile, such as that of Baumard on the chemical diffusivity of oxygen in oxygen-deficient rutile, or that of Izumi on dielectric properties, are also analysed in terms of point defects only. Similar criticisms therefore apply to these articles. In contrast, studies of oxygen-tracer diffusion in rutile and the Ti 02 -i phases by Bagshaw and Hyde are presented clearly, with no extrapolations made about the defect structure of the materials used. 

The thermodynamic factor d ioJdco in Eq. (10.12) can be determined directly from experiment by measuring the oxygen stoichiometry as a function of oxygen partial pressure, either by gravimetric or coulometric measurements. In view of Eqs. (10.6) and (10.7), it comprises contributions from both ionic and electronic defects, which reflect their non-ideal behaviour. For materials with prevailing electronic conductivity Eq. (10.12) may be simplified to yield an exact relation between the chemical diffusion coefficient D and the oxygen tracer diffusion coefficient D ... 

Arita M, Hosoya M, Kobayashi M, Someno M (1979) Depth profile measurement by secondary ion mass spectrometry for determining the tracer diffusivity of oxygen in rutile. J Am Ceram Soc 62 443-446 Bagshaw AN, Hyde, BG (1976) Oxygen tracer diffusion in the magneli phases Tin02n-i J Phys Chem Solids 37 835-838... 

Kalen JD, Boyce RS, Cawley JD (1991) Oxygen tracer diffusion in vitreous silica. J Am Ceram Soc 74 203-209... 

De Souza, R. A., and Kilner, J. A. (1998). Oxygen transport in Lai-j Stj Mni- Co Os+a perovskites—Part 1. Oxygen tracer diffusion. Solid State Ionics 106 175-187. 

Sakaguchi, I., Haneda, H., Tanaka, 1., and Yanagitani, T. (1996). Effect of composition on the oxygen tracer diffusion in transparent yttrium aluminum garnet (YAG) ceramics. J. Am. Ceram. Soc. 79 1627-1632. 

Berenov AV, Atkinson A, Kilner JA, Bucher E, Sine W (2010) Oxygen tracer diffusion and surface exchange kinetics in La0.6Sr0.4CoO3-delta. Solid State Ionics 181 819... 

The chemical diffusion coefficient Dchem and the oxygen tracer diffusion coefficient D are correlated by the thermodynamic factor y ... 

Berenov, A.V., MacManus-Driscoll, J.L, and Kilner, JA. (1999) Oxygen tracer diffusion in undoped lanthanum manganites. Solid State Ionics, 122, 41-49. 

De Souza, R.A., Kilner, JA., and Walker, J.F. (2000) A SIMS study of oxygen tracer diffusion and surface exchange in Lao.sSro.2Mn03+a. Mater. Lett., 43,... 

Lai Sr Mni yCoy03 a perovskites Part I. Oxygen tracer diffusion. Solid State Ionics, 106,175-187. 

Wang, L., Merkle, R., Maier, J., Acartiirk, T., and Starke, U. (2009) Oxygen tracer diffusion in dense... 

The self-diffusion coefficient is usually obtained from measurement of the tracer diffusion coefficient, in this case the oxygen tracer diffusion coefficient D = f D here, / is called the correlation factor and represents the deviation from randomness of the jumps ( 1). We will follow an analysis given in [2, 3] for a material that has an oxygen deficiency accommodated by oxygen vacancies which are mobile, D can be derived in terms of atomistic parameters from random walk theory. 

Fig. 5.9 Relationships between the activation energy of oxygen tracer diffusion and the logarithm of pre-exponential coefficient in ferrites (a), chromates (a), cobaltites (a), manganites (b), titanates (b). The lines are a guide to the eye...

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