First principles study of phase stability and ferroelectric properties of Bi1−xRExFeO3 (RE = Y, La) solid solutions

Abstract

The ferroelectric properties and phase stability of Bi1−xYxFeO3 and Bi1−xLaxFeO3 solid solutions have been investigated from x = 0 to 1 using density functional theory. It was found that BiFeO3 undergoes a phase transition from rhombohedral (space group R3c) to orthorhombic structure at x = 0.15 and 0.32 for Y and La, respectively. Up to x = 0.63 for both systems the polar (space group Pn21a) and non-polar (space group Pnma) orthorhombic phases coexist. For x > 0.63 only the non-polar structure is stable. The effect of hydrostatic pressure on the structural and ferroelectric properties of BiFeO3 has been also investigated. The hydrostatic pressure has the same effect on BiFeO3 as Y substitution. The enhancement of the ferroelectric properties of Bi1−xYxFeO3 for low x arises from the large off-centering of Y-O atoms, which are caused by the small radius of Y atoms and the mixing of 4d-5p orbitals of Y followed by the hybridization of Y-4d and O-2p orbitals. The calculated ferroelectric polarization for the hypothetical rhombohedral YFeO3 structure is 72 μC/cm2.