Ferroelectric phase coexistence by crystallite size reduction in BiFeO₃−PbTiO₃

Abstract

Size effect in ferroelectrics has been extensively investigated in the past with the general consensus that the long-range ferroelectric ordering gradually disappears with decreasing crystallite size, eventually leading to the paraelectric state. In this paper, we show that the compositions exhibiting giant tetragonality ( c / a ∼ 1.18 ) of the ferroelectric alloy system BiFeO₃ − PbTiO₃ transform from a pure tetragonal phase to a state comprising tetragonal and rhombohedral phases as the average crystallite size is reduced from ∼ 10 to ∼ 1 μm. It is argued that the increased surface energy in the smaller sized crystallites creates an equivalent compressive stress that drives the system towards tetragonal-rhombohedral criticality.