Chemical Diffusion and Oxygen Surface Transfer of La[sub 1−x]Sr[sub x]CoO[sub 3−δ] Studied with Electrical Conductivity Relaxation

Abstract

The chemical diffusion coefficient and oxygen-transfer coefficients of selected compositions in the series La 1Ϫx Sr x CoO 3Ϫ␦ were studied using the conductivity relaxation technique. Measurements were performed in the temperature range 600-850°C and oxygen partial pressure 10 Ϫ4 to 1 bar. Chemical diffusivity and oxygen surface transfer in the La 1Ϫx Sr x CoO 3Ϫ␦ perovskites appear to be highly correlated. The general trend displayed is that both parameters decrease with decreasing p O 2 below about 10 Ϫ2 bar at all temperatures. This is attributed to ordering of induced vacancies at low oxygen partial pressures. The observation that the correlation between both parameters extends even to the lowest p O 2 values in this study suggests a key role of the concentration of mobile oxygen vacancies, rather than of the extent of oxygen nonstoichiometry, in determining the rates of both processes. The characteristic thickness L c , which equals the ratio of the chemical diffusion coefficient to the surface transfer coefficient, shows only a weak dependence on oxygen partial pressure and temperature. For different compositions La 1Ϫx Sr x CoO 3Ϫ␦ , L c is found to vary between 50 and 150 m.

A/B-Ratio and Transport Properties of (La0.85Sr0.15)sCoO3?? Perovskites

“…Generally, a relatively constant value of D Chem is observed when changing the oxygen partial pressure. The values at high oxygen partial pressures are in good agreement with measurements made by van der Haar et al [12] who investigated La 0.8 Sr 0.2 CoO 3−δ . We have previously observed that there is a strong correlation between D Chem and k Ex when fitting relaxation curves, especially when k Ex becomes small.…”

Structural and functional properties of SrTi 1−x Fe x O 3−δ (0 ⩽ x ⩽ 1) for the use as oxygen transport membrane

“…During ECR measurements, the normalized conductivity was monitored as a function of time after a step-wise change in the ambient p O 2 from 0.21 to 0.105 atm in the range 700-900°C. The transient conductivity was fitted to the appropriate solution of Fick's second law of diffusion [34].…”

“…8. Diffusion coefficient and surface exchange rates of STF-50, LSCF, and LSC[34] in dependence on temperature.…”

Electrochemical performance and stability of nano-particulate and bi-continuous La1−X Sr X CoO3 and Ce0.9Gd0.1O1.95 composite electrodes

“…It has been shown using conductivity relaxation data that the kinetic constant for the oxygen surface exchange reaction (k EX ) of LSC has a relatively strong P O2 dependence (k EX ∝(P O2 ) −n with n approximately equal to 0.5 [21,22]. In contrast, the oxygen vacancy diffusion is relatively independent on P O2.…”