Trapping a Metastable Ferroelectric Phase by Size Reduction in Semiconducting Ferroelectric BiFeO₃-PbTiO₃ and Its Implications for Photocatalytic Response

We show that the large elastostatic and electrostatic energies associated with the supertetragonal spontaneous strain and polarization of a semiconducting ferroelectric (1-x)BiFeO3-(x)PbTiO3 forces the ground state to switch to the rhombohedral (R) ferroelectric phase on reduction of crystallite size. The continuity of the pinned tetragonal domain walls, however, prevents a direct tetragonal-to-rhombohedral transformation as the size is gradually reduced by physical means at room temperature. The trapped metastable tetragonal phase in the small crystallites is found to show significantly enhanced photocatalytic activity as compared to its stable tetragonal- or rhombohedral-phase counterparts. Our study suggests that the size effect in multidomain ferroelectrics can be exploited as an effective strategy for the manipulation of functional properties.