The n = 3 member of the SrCoO(3n − 1)/n series of layered oxygen-defect perovskites

Topotactic oxygen deintercalation from cubic perovskite oxide SrCoO3 − δ (δ < 0.25) is realized in a controlled way at low temperatures. Annealing in air at 200 < T < 275 °C results in a three-phase region within 0.25 < δ < 0.50. Two of the phases are known previously, namely SrCoO2.5, a phase with an orthorhombic brownmillerite-type (BM) structure, and SrCoO2.75 (T1), a phase with a slight tetragonal distortion from cubic symmetry. The third phase (T2) has a strong tetragonal distortion, and appears to be the missing n = 3 member of the SrCoO(3n − 1)/n series. Once the overall oxygen content reaches the value of (3 − δ)aver = 2.68(1), the T1-to-T2 phase conversion proceeds at constant (3 − δ)aver. A more pronounced evolution of the cT2 lattice parameter as compared to the aT2 parameter implies a layered oxygen-vacancy-ordered structure for T2 with some flexibility for oxygen-content variation, in the style of the BM phase.

Graphical abstractTopotactic oxygen deintercalation from cubic perovskite SrCoO3 − δ (δ < 0.25) is realized in a controlled way at low temperatures. Annealing in air at 200 ≤ T ≤ 275 °C results in a three-phase region within 0.25 < δ < 0.50. A new unstable tetragonal phase SrCoO2.68 − z was detected for the first time.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Topotactic deintercalation of oxygen from cubic SrCoO3 − δ perovskite is realized at low temperatures. ► Low-temperature annealing in air results in a three-phase region within 0.25 < δ < 0.50. ► One of the three phases is the missing n = 3 member of the SrCoO(3n − 1)/n series. ► The new n = 3 phase has a layered oxygen-vacancy-ordered structure. ► n = 3 phase shows some flexibility for oxygen-content variation.