Oxygen chemical diffusion in strontium doped lanthanum manganites

The chemical diffusion coefficient of oxygen in (La 0.79Sr 0.20)MnO 3−δ and (La 0.50Sr 0.50)MnO 3−δ was measured in a solid state electrochemical cell using the potentiostatic step method. In the temperature range between 700°C and 860°C, the chemical diffusion coefficient of oxygen in (La 0.79Sr 0.20)MnO 3−δ was found to be in the range of 10 −8 to 10 −6 cm 2/s and also strongly dependent on the oxygen partial pressure between 0.21 atm and 10 −8 atm. For the case of the stoichiometric oxygen content, the activation energy for oxygen chemical diffusion in this material was determine to be about 70 kJ/mole. Similar measurements between 700°C and 840°C using samples of the composition (La 0.50Sr 0.50)MnO 3−δ yielded comparable diffusion coefficient values. Such rapid oxygen transport in these materials make them attractive for high temperature fuel cell electrode and gas separation membrane applications. They also exhibited unusually high values of the order of 10 3 to 10 4 for the thermodynamic enhancement factor indicative of narrow oxygen nonstoichiometry.