Sequence of structural transitions in BiFeO3–RMnO3 thin films (R=Rare earth)

The BiFeO3 (BFO)–RMnO3 (R=rare earth) system affords an interesting combination of good ferroelectric polarization and magnetization properties at room temperature that is prerequisite for intrinsic multiferroism. In the present work we report on the structural properties of the BFO–RMnO3 (R=Ho, Gd, La) solid solution in a range of concentrations. Using XRD and particularly Raman scattering we show the BFO–RMnO3 system undergoes a structural transition from monoclinic toward ferroelectric orthorhombic structure for RMnO3 concentrations of up to 10% and beyond it to paraelectric pseudo tetragonal structure for large ions or to pseudocubic for the small ones. The phase transitions are explained in terms of the change of the nature of octahedral distortion which is found to be sensitive to the concentration and size of the rare earth element, and the presence of manganese.