Scaling of extended defects in nano-sized Brownmillerite CaFeO2.5

Kapil Gupta (1) , Shubra Singh (2, 3) , Monica Ceretti (2) , M.S. Ramachandra Rao (1) , Werner Paulus (2)

1 Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre
2 ICGM ICMMM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier
3 Crystal Growth Centre

We investigated the formation of extended defects in CaFeO2.5, predominantly appearing as antiphase boundaries (APBs), as a function of the synthesis method and temperature. While CaFeO2.5 is known to adopt an ordered oxygen defect structure showing long range order of the (FeO4)∞ chains in its bulk form, interestingly, we demonstrated that the length of these (FeO4)∞ chains can be considerably scaled down to few nanometers by adopting a modified sol-gel method (low temperature synthesis) while the grain size of the resulting nano-phase CaFeO2.5 is around 50 nm. We discuss the synthesis dependent modulation of the length of APBs, characterized by X-ray diffraction and high resolution TEM, to be at the origin of an amplified switching dynamics of the (FeO4)∞ chains. This can accordingly explain the reduction of the onset temperature for oxygen diffusion to set in from 450 °C for bulk-CaFeO2.5 to 320 °C for nano-CaFeO2.5, as determined by 18O/16O oxygen isotope exchange reactions

Domaines: Matériaux; Science des matériaux [cond-mat.mtrl-sci]

Kapil Gupta, Shubra Singh, Monica Ceretti, M.S. Ramachandra Rao, Werner Paulus. Scaling of extended defects in nano-sized Brownmillerite CaFeO2.5. physica status solidi (a), 2013, 210 (9), pp.1771-1777. ⟨10.1002/pssa.201329027⟩. ⟨hal-00875691⟩