Metastable morphotropic phase boundary state in the multiferroic BiFeO₃–PbTiO₃

Abstract

Temperature-time study of the magnetoelectric multiferroic (1-x)BiFeO₃-(x)PbTiO₃ by x-ray and electron diffraction on the reported morphotropic phase boundary (MPB) compositions revealed that this MPB does not correspond to the equilibrium state. The MPB like state is rather of metastable nature and arise due to kinetic arrest of metastable rhombohedral (R3c) phase, along with the equilibrium tetragonal (P4mm) phase. The life time of the metastable R3c nuclei is very sensitive to composition and temperature, and nearly diverges at x → 0.27. The MPB like state appears only if the system is cooled before the metastable R3c nuclei could vanish. These findings resolve the long standing controversy with regard to seemingly erratic phase formation behaviour reported by different groups and provides a rational basis for developing genuine equilibrium MPB compositions in this system for better piezoelectric properties.