Equilibrium phases in the multiferroic BiFeO₃-PbTiO₃ system – a revisit

¹ Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India
² Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II). Technische Universität München, Lichtenbergestrasse 1, D-85747 Garching b. München, Germany

^a Corresponding author: kothai@materials.iisc.ernet.in

Published online: 3 July 2014

Abstract

The(1-x) BiFeO₃-(x) PbTiO₃ solid solution exhibiting a Morphotropic Phase Boundary (MPB) has attracted considerable attention recently because of its unique features such as multiferroic, high Curie point (TC ~ 700°C) and giant tetragonality (c/a -1 ~ 0.19). Different research groups have reported different composition range of MPB for this system. In this work we have conclusively proved that the wide composition range of MPB reported in the literature is due to kinetic arrest of the metastable rhombohedral phase and that if sufficient temperature and time is allowed the metastable phase disappears. The genuine MPB was found to be x=0.27 for which the tetragonal and the rhombohedral phases are in thermodynamic equilibrium. In-situ high temperature structural study of x=0.27 revealed the sluggish kinetics associated with the temperature induced structural transformation. Neutron powder diffraction study revealed that themagnetic ordering at room temperature occurs in the rhombohedral phase. The magnetic structure was found to be commensurate G-type antiferromagnetic with magnetic moments parallel to the c-direction (of the hexagonal cell). The present study suggests that the equilibrium properties in this solid solution series should be sought for x=0.27.