Chemical diffusivities in dense polycrystalline specimens were measured, using a thermomicrobalance, at temperatures ranging from 650 to 900C and O partial pressures ranging from 0.01 to 1atm. It was found that the relaxation, which occurred after a step-change in O pressure from 0.3 to 0.01atm, was exponential. The reduction rate coincided with that of oxidation. It was concluded that the relaxation obeyed diffusion-controlled kinetics. The O self-diffusion coefficient (table 109) and the O vacancy diffusion coefficient were deduced from the chemical diffusion coefficient. The latter could be described by the expression:

D (cm2/s) = 0.0531 exp[-18(kcal/mol)/RT]

while the self-diffusivity was described by:

D (cm2/s) = 0.0851 exp[-33(kcal/mol)/RT]

It was noted that the O self-diffusivity in the present material was slightly higher than that in perovskites, and lower than that in Cu3Ba2YO6.4. The vacancy diffusion coefficient was given by:

D (cm2/s) = 0.0163 exp[-18(kcal/mol)/RT]

and was almost the same as that in perovskite-type oxides.

Y.Idemoto, K.Fueki, M.Sugiyama: Journal of Solid State Chemistry, 1991, 92[2], 489-95

Table 109

Diffusion of O in Nd2CuO4