Ferroic transitions in the multiferroic (1 − x)Pb(Fe1/2Nb1/2)O3–xPbTiO3 system and its phase diagram

The results of the first comprehensive study of ferroic phase transitions as a function of temperature and compositions in the mixed multiferroic (1 − x)Pb(Fe1/2Nb1/2)O3–xPbTiO3 (PFN–xPT) system are reported. Temperature-dependent powder synchrotron X-ray diffraction studies confirm unambiguously an interferroelectric transition between monoclinic and tetragonal phases for x ⩽ 0.10. The tetragonal phase of PFN–xPT for x ⩽ 0.10 and x > 0.10 is found to transform to the cubic phase on heating above room temperature. All these transitions are accompanied by distinct anomalies in the temperature dependence of dielectric constant. Our magnetization studies reveal that the nature of the magnetic phase transition changes across the morphotropic phase boundary (MPB) composition of PFN–xPT such that for tetragonal compositions with x > 0.08 there is only one magnetic transition, whereas two antiferromagnetic transitions are observed for monoclinic compositions with x < 0.08. These studies have enabled us to construct a phase diagram of PFN–xPT for the first time.