Unconventional mechanism of stabilization of a tetragonal phase in the perovskite ferroelectric (PbTiO3)1-x(BiFeO3)x

Temperature-dependent x-ray powder-diffraction study of the tetragonal compositions of PbTiO3-BiFeO3 series has revealed that, unlike for all the known ferroelectric perovskites, the compositions exhibiting giant tetragonality is stabilized from the cubic phase via a complex transition pathway which involve (i) formation of minor monoclinic phase with a large pseudotetragonality along with an intermediate tetragonal phase (major) with a small tetragonality, (ii) gradual vanishing of the intermediate tetragonal phase and concomitant increase in the monoclinic regions, and finally (iii) gradual transformation of the monoclinic phase to the tetragonal phase with giant tetragonality. The system seems to adopt such a complex transition pathway to create a microstructure with very large number of domains and interfaces for stress relief, which would not have been possible in case of a direct cubic-tetragonal transition.