The local atomic structure and nanoscale chemistry of an antipolar phase in Bi0.9Sm0.1FeO3 epitaxial thin Films are examined by an array of transmission electron microscopy (TEM) coupled with electron diffraction and electron energy-toss spectroscopy methods. The observations are tied to macroscopic properties of the Films, namely, polarization-electric Field hysteresis loops, dielectric constant-electric field hysteresis loops, and the dielectric loss. At room temperature, the local Sm deficiency was determined to destabilize the long-range ferroelectric state, resulting in the formation of local antipolar clusters with the appearance or PbzrO(3)-like antiparallel cation displacements, which give rise to (1)/(4){011} and (1)/(4){211} reflections as well as (1)/(2){321}, because of in-phase oxygen octahedral tilts Aberration-corrected TEM analysis reveals that the antipolar structure is actually a lamellar of highly dense ferroelectric domains with alternating polarizations With increasing temperature, a phase transition was observed at 150 degrees C, which is attributed to the reduction of the antiparallel displacements, giving way to cell-doubline, structural transition