A group-theoretical analysis was carried out to determine the possible orientation states of domains formed as a result of the 'perovskite-brownmillerite' phase transition in SrCo0.8Fe0.2O2.5 oxide with mixed ion-electron conductivity (MIEC). The results of the theoretical analysis agree with the experimental data obtained in the study of the SrCo0.8Fe0.2O2.5 microstructure by means of transmission electron microscopy. Brownmillerite SrCo0.8Fe0.2O2.5 (BM) has a lamellar texture composed of 90° twins 60-260nm in size; the 010BM and 101BM directions are linked through twinning in accordance with the predictions of the group-theoretical analysis. The presence of twins and their switching under mechanical load provide evidence that the perovskite-brownmillerite phase transition in SrCo0.8Fe0.2O2.5 is ferroelastic. Comparative analysis of the phenomena observed for ferroelectrics and MIEC oxides indicates their similarity based on the common nature of ferroelectricity and ferroelasticity, and allows us to suppose that nonstoichiometric SrCo0.8Fe0.2O3-δ with compositional disorder may be considered (in terms of its microstructural features) a 'relaxor ferroelastic'.
- Oxygen-deficient perovskites
- ferroelastic phase transitions
- group-theoretical analysis
- mixed electron-ion conducting oxides