Strain-induced isosymmetric phase transition inBiFeO3

Abstract

We calculate the effect of epitaxial strain on the structure and properties of multiferroic bismuth ferrite, ${\text{BiFeO}}_3$, using first-principles density-functional theory. We investigate epitaxial strain corresponding to an (001)-oriented substrate and find that, while small strain causes only quantitative changes in behavior from the bulk material, compressive strains of greater than 4% induce an isosymmetric phase transition accompanied by a dramatic change in structure. In striking contrast to the bulk rhombohedral perovskite, the highly strained structure has a $c/a$ ratio of $\sim 1.3$ and five-coordinated Fe atoms. We predict a rotation of polarization from [111] (bulk) to nearly [001], accompanied by an increase in magnitude of $\sim 50\mathrm{\%}$, and a suppression of the magnetic ordering temperature. Our calculations indicate critical strain values at which the two phases might be expected to coexist and shed light on recent experimental observation of a morphotropic phase boundary in strained ${\text{BiFeO}}_3$.