Structure determination of a brownmillerite Ca2Co2O5 thin film by precession electron diffraction

Calcium cobaltite thin films with a nominal ratio Ca/Co=1 were grown on (101)-NdGaO3 substrate by the pulsed laser deposition technique. The structure of the as-deposited metastable phase is solved using a precession electron diffraction three-dimensional data set recorded from a cross-sectional sample. We found that an ordered oxygen-deficient Ca2Co2O5 perovskite of the brownmillerite type with lattice parameters a approximate to a(p) root 2 approximate to 5.46 angstrom, b approximate to 4a(p) approximate to 14.88 angstrom, and c approximate to a(p) root 2 approximate to 5.46 angstrom (space group: Ibm2) has been stabilized using the substrate-induced strain. The structure and microstructure of this metastable cobaltite are further discussed and compared to related bulk materials based on our transmission electron microscopy investigations. The present results open the route to the resolution of metastable phases prepared in the form of a thin film using the precession electron diffraction and should be useful for the solid state chemistry community.