Morphotropic phase boundary (MPB) systems are characterized by the coexistence of two ferroelectric phases and are associated with anomalous piezoelectric properties. In general, such coexistence is brought about by composition induced ferroelectric-ferroelectric instability. Here we demonstrate that a pure ferroelectric compound Na${}_{1/2}$Bi${}_{1/2}$TiO${}_3$ (NBT) exhibits the coexistence of two ferroelectric phases, rhombohedral ($R$3$c$) and monoclinic ($Cc$), in its equilibrium state at room temperature. This was unravelled by adopting a unique strategy of comparative structural analysis of electrically poled and thermally annealed specimens using high resolution synchrotron x-ray powder diffraction data. The relative fraction of the coexisting phases was found to be highly sensitive to thermal, mechanical, and electrical stimuli. The coexistence of ferroelectric phases in the ground state of the pure compound will have significant bearing on the way MPB is induced in NBT-based lead-free piezoceramics.

• Received 15 November 2012

DOI:https://doi.org/10.1103/PhysRevB.87.060102