Search

Nonstoichiometry of the perovskite-type solid solutions La0.9Ca0.1Cr1−yAlyO3−δ was studied by high-temperature gravimetry under controlled P(O2) atmospheres of 1–10− 23 bar at 1073–1273 K. The observed data were described by a regular solution-like model for the randomly distributed defects of VO¨∙∙, CrCr.∙, CaLa,, and AlCrX. With the increase in y, VO¨ ∙∙ formation becomes much easier. For y > 0.8, some fraction of CaLa, becomes surrounded only by AlCrX and VO¨∙∙ remains around such CaLa, up to high P(O2) to reduce the maximum oxygen content below 3.000. [Copyright &y& Elsevier]

The chemical stability of perovskite-type La1−xCaxCrO3−δ (x=0.1, 0.2, 0.3) in high oxygen partial pressure, PO2, was investigated with three methods: thermogravimetry, XRD analysis, and thermodynamic calculation. The second phase, CaCrO4 was observed by XRD analysis on the powder equilibrated in high PO2. Thermogravimetry under fixed temperatures sensitively detected the segregation of the second phase in the form of oxygen incorporation, because oxidation of chromium ion accompanies the segregation. The second phase tended to appear in high PO2 and at low temperature. The single-phase regions of La1−xCaxCrO3−δ obtained from the two experimental methods well agreed with each other. The results of thermodynamic calculation on the assumption of ideality of the solid solution also agreed with the experimental results. These results suggested the sufficient chemical stability of La1−xCaxCrO3−δ in high PO2 concerning the application to an interconnector of high-temperature solid oxide fuel cells; for example, La0.7Ca0.3CrO3−δ is stable at 1273K in air. [Copyright &y& Elsevier]