Ferroelectricity and Elasticity of Rhombohedral BiFeO3 Under Uniaxial Stress

We report on first-principles calculations of electric polarization in multiferroic rhombohedral BiFeO3 under the [111] uniaxial stress, and our results suggest that the polarization varies nearly linearly from 75.5 to 97.1Ccm(-2) within the stress range of 8 to -8GPa. The change of polarization is mainly due to atomic displacements since the calculated Born effective charges barely change under stress. We also compute the elastic stiffness coefficients and the elastic compliance coefficients, and these results demonstrate that the rhombohedral structure of BiFeO3 remains stable under the uniaxial stress between 8 and -8GPa. Because in a ferroelectric-based photovoltaic cell the photocurrent is proportional to the magnitude of electric polarization, it is possible to improve the photovoltaic efficiency of BiFeO3 thin film by applying uniaxial stress.