Intermediate structural phases in rare-earth substituted BiFeO3

The room-temperature crystal structure and local ferroelectric properties of Bi0.85RE0.15FeO3 (RE = Sm, Gd, Dy) polycrystalline samples have been investigated by X-ray diffraction (XRD) and piezoresponse force microscopy (PFM) techniques. XRD measurements show that the rare-earth substitution causes the transformation of R3c structure typical of BiFeO3 to yield orthorhombic phases with √2a × 2√2a × 2a and √2a × 2a × √2a superlattices (a is the parameter of the cubic perovskite subcell). Results of PFM investigations imply that both the orthorhombic phases are polar. The models describing crystal structure of the phases are discussed.