Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo_2O_(5.5 + δ)(LBCO) thin films grown on SrTiO_3(STO) substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]_(LBCO)//[100]_(STO)and(001)_(LBCO)//(001)_(STO). Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 90℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001]direction of the film. In the film grown at a temperature of 1000℃, isolated nano-scale Co_3O_4 particles appeared, which promoted the growth of {111} twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.
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