Nonstoichiometry and transport properties of strontium-substituted lanthanum cobaltites

Abstract

In La 1− x Sr x CoO 3− δ (LSC), the oxygen nonstoichiometry and transport properties change with variations in Sr content, temperature and oxygen partial pressure. The purpose of this study was to investigate and correlate these parameters. The extent of oxygen deficiency was investigated by oxygen exchange measurements over the range from 300 to 900 °C and 1.9×10 −2⩾ p O 2 ⩾1.0×10 −4 bar. The oxygen deficiency was found to increase with decreasing oxygen partial pressure and/or increasing temperature. The chemical diffusion coefficient and the surface oxygen exchange coefficient were determined simultaneously by fitting transient re-equilibration curves to the respective diffusion equation at T=725 °C. The electronic conductivity was studied as a function of temperature and oxygen partial pressure at 1.9×10 −2≤ p O 2 ≤1.0×10 −4 bar. Furthermore, these data were correlated with those of the nonstoichiometry to yield conductivity values for constant oxygen content. In the case of La 0.6Sr 0.4CoO 3− δ (LSC04), the temperature dependence of the isostoichiometric conductivities yields activation energies of 0.02≤ E a≤0.05 eV.