Chemical diffusion in calcium titanate

This work reports the gas/solid equilibration kinetics for the O ₂/CaTiO₃ system. The electrical conductivity measurement was applied for monitoring the kinetics in the ranges of temperature 973-1323 K and oxygen partial pressure 10Pa-72kPa. It was found that the gas/solid equilibration kinetics for the polycrystalline CaTiO₃ specimen in the above experimental conditions is 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 p(O₂), respectively: D _chem=1.28×10^-4exp(-134.4(kJ/mol)/RT (m ²s^-1) D_chem=3.47×10^-6exp(-65. 9(kJ/mol)/RT (m²s^-1) It was found that the chemical diffusion coefficient increases with p(O₂). This effect, that is limited to the temperature range 1073-1323 K, indicates that the mobility of the defects is inversely proportional to the concentration of oxygen vacancies. The chemical diffusion coefficient at 973 K is independent of p(O₂). The activation energy of the obtained diffusion data (65.9 and 134.4 kJ/mol at high and low p(O₂), respectively) is considered in terms of the effect of p(O₂) on the mobility of ionic charge carriers (oxygen vacancies).