Delicate Balance among Three Ferroic Polymorphic Phases in BiFeO3-BiMnO3-PbTiO3

International audiencePhase-change functional responses can be obtained in perovskite solid solutions at structural instabilities involving multiferroic states, a very promising approach for realizing magnetoelectric effects at room temperature. A line of multiferroic morphotropic phase boundaries (MPBs) has been described within the phase diagram of the BiFeO3-BiMnO3-PbTiO3 ternary system, in which an evolution from Cc/P4mm-type (polar/polar) to Pnma/P4mm-type (antipolar/polar) MPBs takes place. Coexistence of the three polymorphs results in a small region, where distinctive phase-change magnetoelectric responses are anticipated. In this work, all three polymorphs were obtained, either isolated or in phase coexistence with varying percentages, by tailoring the cooling profile after high-temperature annealing in a small compositional range. The perovskite structure was characterized, and temperature-dependent magnetic and electrical characterizations were carried out to define the ferroic orders and crystal physicochemical properties of the three polymorphs. Results revealed the close interplay among the crystal structure, point defects, and multiferroism in this small region, where the delicate balance among the three polymorphs is shown. Additionally, the effect of size reduction across the submicron range, down to the nanoscale, is described and discussed