First-principles study of the coexisting ferroelectric and ferromagnetic properties of the La_0.75Bi_0.25CrO₃ compound

Despite the interesting properties of La1-xBixCrO3, the origin of its multiferroic properties has not been yet established by first-principles calculations. Toward this effect, in this work we present a comparative study between the structural, electronic, magnetic and ferroelectric properties of pristine LaCrO3 and La0.75Bi0.25CrO3 using density functional theory (DFT) plus the Hubbard potential (U) formalism and the Berry phase approach for the polarization. Additionally, we present a comparative analysis between reported experimental results and the theoretical calculations of this work, from which we have determined that LaCrO3 is stable under a G-type antiferromagnetic configuration, while the La0.75Bi0.25CrO3 is stable in a ferromagnetic one. This is due to the decrease of the Cr-O-Cr angle which is strongly related to the high degree of covalence of the spin-up Cr-t(2g) and O-2p orbitals in the Cr-O bonds. On the other hand, La0.75Bi0.25CrO3 turns out to be ferroelectric due to the structural distortion induced by the lone pair of Bi in site A, which predicts a spontaneous polarization of 30.41 mu C/cm(2) in the [011] direction. That is, first-principles calculations satisfactory explain the origin of ferromagnetism and ferroelectricity of the La1-xBixCrO3 compound.