Designing multiferroic phase boundaries in the BiFeO3-BiMnO3-PbTiO3 ternary system: Phase-change responses and property enhancement

Research activity in magnetoelectric multiferroics is being extensive and driven toward novel approaches for obtaining compounds with either linear magnetoelectric effects or crossed switching phenomena at room temperature,... [ view full abstract ]

Research activity in magnetoelectric multiferroics is being extensive and driven toward novel approaches for obtaining compounds with either linear magnetoelectric effects or crossed switching phenomena at room temperature, for they would enable a range of potentially disruptive technologies (e.g., voltage-tunable spintronic devices, uncooled magnetic sensors, and magnetoelectric memories). A topical set of materials are ABO₃ perovskite oxides, in which multiferroicity can be chemically engineered by placing ferroelectrically and magnetically active cations in A- and B-site, respectively. This is the case of BiFeO₃ and BiMnO₃, and of the solid solutions they form with PbTiO₃. Interest in these systems is fostered by the presence of multiferroic morphotropic phase boundaries (MPBs), and in particular the occurrence of phase-change magnetoelectric responses in the case of BiFeO₃-PbTiO₃.

Here, we review and update our research activity in the BiFeO₃-BiMnO₃-PbTiO₃ ternary system, whose phase diagram is liable to present differentiated MPBs. Neutron diffraction and high-resolution XRD, along with Rietveld refinement, are used to establish the phase symmetry and phase coexistence. A comprehensive analysis of the crystal structure and multiferroism across the different MPBs is presented, based on electrical, magnetic and magnetoelectric characterizations, complemented with mechanical and electromechanical measurements.

BiFeO₃-rich compositions showed multiferroic MPBs between non-magnetic/ferroelectric tetragonal P4mm phase and antiferromagnetic/ferroelectric monoclinic Cc one. Distinctive room-temperature magnetoelectric responses resulted by means of two mechanisms: field-driven phase-changes and transverse lattice softening. While BiMnO₃-rich compositions showed a polar/non-polar MPB formed by tetragonal P4mm phase and an antiferroelectric orthorhombic Pnma one. The role of the complex defect chemistry, where Bi/Pb-deficiency allowed the Mn and Fe ions to present mixed-valence states, on the delicate balance between the polymorphs is investigated.

[1] C.M. Fernández-Posada et al. Nat. Commun. 7, 12772 (2016)

[2] C.M. Fernández-Posada et al. J. Mater. Chem. C, 3, 2255 (2015)

[3] H. Amorín et al. J. Appl. Phys., 115,104104 (2014)