Oxygen cycling in half-doped Ln_1-xSr_xCoO_3−δ cobalt perovskite oxides and in situ neutron diffraction study of Pr_0.5Sr_0.5CoO_3−δ

Ln_1–xSr_xCoO_3−δ perovskite oxides are important mixed ionic electronic conductors with applications in electrochemical energy conversion. This manuscript reports a systematic investigation of the oxygen cycling capacity of a wide range of half-doped x = 0.5 compositions from Ln = La–Y using thermogravimetric analysis. A similar upper limit δ_max = 0.35–0.40 is found, with the variation in storage capacity resulting from the highest accessible oxygen content (δ_min). The best oxygen storage capacity of ∼0.3 mol O corresponding to ∼2 wt % is found for Ln = Pr–Sm. For Ln = Gd–Y, A-site ordered superstructures are found, linked to a deviation from the ideal 1:1 Ln:Sr stoichiometry, with compositions becoming more Sr-rich. These samples have notably reduced oxygen storage capacities. In situ neutron powder diffraction was used to probe the structural evolution of Pr_0.5Sr_0.5CoO_3−δ under flowing nitrogen gas. This revealed extensive domains of phase coexistence between Imma, R3̅c, and cubic perovskite structures. Significant oxygen loss occurs above 450 °C at which point the cubic phase is the largest component of the sample. This study contributes new insight into structural stability and oxygen cycling performance of these important electrode materials.