Electrical conductivity relaxation measurements were performed on thin specimens of La1-xSrxFeO3, where x was equal to 0.1 or 0.4, at O partial pressures of between 10-5 and 1bar and temperatures ranging from 923 to 1223K. The transient response of the conductivity, following a sudden change in the ambient O partial pressure, was analyzed in the frequency domain. This permitted diffusion-limited and surface exchange-limited re-equilibration kinetics to be separated. The response of specimens which were 350 to 460μ thick indicated the operation of diffusion-controlled kinetics at partial pressures above 0.03bar. The chemical diffusivity was found to be independent of the O partial pressure. At 1073K, it was equal to 6.5 x 10-6cm2/s for x = 0.1 and to 1.1 x 10-5cm2/s for x = 0.4 (table 4), with an activation energy of about 80kJ/mol. The equilibration process was governed by surface exchange at pressures below 0.01bar. The surface exchange coefficient was proportional to the O partial pressure, raised to a power of between 0.65 and 0.85. This dependence was explained in terms of a slow surface process which involved an O molecule and a surface O vacancy (table 5), and caused the sharp transition from diffusion-controlled to exchange-controlled kinetics. The activation energy for surface exchange was estimated to be between 110 and 135kJ/mol.

J.E.Ten Elshof, M.H.R.Lankhorst, H.J.M.Bouwmeester: Journal of the Electrochemical Society, 1997, 144[3], 1060-8

Table 4

Chemical Diffusivity in La1-xSrxFeO3

Table 5

Oxygen Vacancy Diffusivity in La1-xSrxFeO3