Structural transitions and complex domain structures across a ferroelectric-to-antiferroelectric phase boundary in epitaxial Sm-doped BiFeO3 thin films

We have investigated structural phase transitions across a ferroelectric-to-antiferroelectric phase boundary in epitaxial (001) oriented Bi(1-x)SmxFeO3 thin films. For the Sm3+ concentration of 0.1 < x < 0.14, we observe short-range antiparallel cation displacements, verified by the appearance of localized 14{011} weak reflections in the selected area electron diffraction patterns. At the critical composition of x=0.14, the system adopts a complex nanoscale domain mixture with appearance of 14{011}, 12{011}, 12{010}, and 12{111} reflections and an incommensurate phase bridging the rhombohedral and orthorhombic phases. For compositions 0.14 < x < 0.2, orientational twin domains coupled with antiphase oxygen octahedral tilts, identified by 12{hkl} weak superstructure are observed. The above systematic changes in the microstructure as a function of Sm3+ doping are linked to the macroscopic functional properties.