The O tracer diffusion was measured in polycrystals at temperatures ranging from 400 to 700C, under O2 partial pressures that varied from 103 and 105Pa. The depth profiles were determined by means of secondary ion mass spectrometry. The results (table 63) could be described by the Arrhenius relationship:

D (cm2/s) = 0.08 exp[-201(kJ/mol)/RT]

It was found that the diffusion coefficient was a sensitive function of the partial pressure, and increased as the partial pressure decreased. The O diffused several orders of magnitude more slowly in the present material than in Cu3Ba2YO7; with a higher pre-exponential factor and a higher activation energy. The clear dependence upon partial pressure indicated that the diffusion of O in polycrystalline samples of the present material occurred via a different mechanism to that in the other oxide. The results of tracer measurements which were performed, at 600 or 700C, on c-axis single crystals indicated that diffusion in the c-direction was at least 100 times slower than diffusion in polycrystals, and involved a larger activation energy.

J.L.Routbort, S.J.Rothman, J.N.Mundy, J.E.Baker, B.Dabrowski, R.K.Williams: Physical Review B, 1993, 48[10], 7505-12

Table 63

Diffusivity of O in Cu4Ba2YO8