This work reports the gas/solid equilibration kinetics for the O2/CaTiO3 system. The electrical conductivity measurement was applied for monitoring the kinetics at 973 to 1323K and 10Pa to 72kPa. It was found that the gas/solid equilibration kinetics for the polycrystalline CaTiO3 specimen in the above experimental conditions was determined by bulk diffusion rather than by grain boundary conditions. The obtained data of the electrical conductivity vs. time were used for the determination of the chemical diffusion coefficient as a function of temperature at low and high PO2, respectively:

D (m2/s) = 1.28 x 10-4 exp[-134.4(kJ/mol)/RT]

D (m2/s) = 3.47 x 10-6 exp[-65.9(kJ/mol)/RT]

It was found that the chemical diffusion coefficient increased with PO2. This effect, that was limited to 1073 to 1323K, indicated that the mobility of the defects was inversely proportional to the concentration of O vacancies. The chemical diffusion coefficient at 973K was independent of PO2. The activation energy of the obtained diffusion data (65.9 and 134.4kJ/mol at high and low PO2, respectively) was considered in terms of the effect of PO2 on the mobility of ionic charge carriers (oxygen vacancies).

Chemical Diffusion in Calcium Titanate. T.Bak, J.Nowotny, C.C.Sorrel: Journal of Physics and Chemistry of Solids, 2004, 65[7], 1229-41