The tracer diffusivity of 18O in dense polycrystalline samples, or in the c-axis direction of monocrystals, was measured at temperatures ranging from 300 to 700C, under an O partial pressure of 1atm. Penetration profiles were obtained by means of secondary ion mass spectrometry. It was found that the results for polycrystalline material could be described by:

D (cm2/s) = 1.7 x 10-5 exp[-0.93(eV)/kT]

while the results for c-axis migration (table 47) could be described by:

D (cm2/s) = 6 x 10-1exp[-2.20(eV)/kT]

The ratio of the 2 values was large, and temperature-dependent. It was concluded that diffusion in the ab-plane and the c-axis direction involved different mechanisms.

Tracer Diffusion of Oxygen in Bi2Sr2CaCu2Ox. M.Runde, J.L.Routbort, S.J.Rothman, K.C.Goretta, J.N.Mundy, X.Xu, J.E.Baker: Physical Review B, 1992, 45[13], 7375-82

[439] Bi2Ga4O9: O Diffusion

Bi2M4O9 (M = Al, Ga, Fe) mullite-type compounds were currently being investigated with respect to their potential application as oxygen ion conductors or mixed ionic-electronic conductors. In the framework of these studies oxygen transport in (nominally) undoped and Sr-doped single crystals of Bi2Ga4O9 was of prime interest. 18O tracer diffusion in combination with secondary ion mass spectrometry depth profiling reveals that oxygen transport occurs via oxygen vacancies introduced by impurities of cations with lower valences in the undoped crystals grown by the top-seeded solution growth method. The fairly small enhancement of the oxygen diffusivity due to Sr doping led to the conclusion that the solubility of Sr in Bi2Ga4O9 was extremely low with respect to the melt during the single crystal growing process. The measured enthalpies of activation (163kJ/mol for undoped and 140kJ/mol for Sr-doped Bi2Ga4O9, respectively) must be considered as migration enthalpies.

Oxygen-18 Tracer Diffusion in Nominally Undoped and Sr-Doped Single Crystals of Mullite-Type Bi2Ga4O9. P.Fielitz, G.Borchardt, M.Burianek, J.Ottinger, M.Mühlberg, T.M.Gesing, R.X.Fischer, H.Schneider: Solid State Ionics, 2012,  221, 40-2

Table 46

Bulk Diffusivity of 110Ag in Bi2Sr2CuOx