Competing phases in BiFeO3 thin films under compressive epitaxial strain
Résumé
Combining density-functional calculations and x-ray diffraction experiments, we show that BiFeO3 epitaxially grown under compressive strain on cubic substrates evolves from the monoclinic Cc phase resulting from the strain-induced deformation of the ground-state rhombohedral R3c phase to the monoclinic Cm phase with increasing misfit, the transition being at about −4.5%/−5.5%. Moreover, the polarization of the Cc phase only rotates instead of increasing for misfit strain ranging from 0% to −4%, due to a strong coupling between polar displacements and oxygen octahedra tilts. This strong interaction is of interest for multiferroics where usually both structural degrees of freedom coexist.
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