Strong phase-change magnetoelectric responses have been anticipated by a first-principles investigation of phases in the perovskite BiFeO 3 -BiCoO 3 solid solution, specifically at the morphotropic phase boundary (MPB) between the multiferroic rhombohedral and tetragonal polymorphs. This might be a general property of multiferroic MPBs and a novel promising approach for room temperature magnetoelectricity, which requires the identification of suitable material systems. We present here a comprehensive description of the electrical and electromechanical properties across one such system; the perovskite BiFeO 3 -PbTiO 3 solid solution. All the temperature dependence of dielectric permittivity, ferroelectric hysteresis loops, and piezoelectric coefficients have been obtained, and are discussed in relation to the previously reported perovskite structural evolution. Results show ceramic materials to be very promising for ferroelectric random access memories (remnant polarization as high as 63 lC cm À2 with a comparatively low coercive field of 4.5 kV mm À1 for MPB compositions) and high temperature electromechanical transduction (crystal piezoelectric coefficient of 87 pC N À1 with a Curie temperature above 873 K). Moreover, the occurrence of phase changes between the monoclinic and tetragonal polymorphs under high electric fields is indicated, while the canted antiferromagnetic character of the phases involved is corroborated. V C 2014 AIP Publishing LLC.

There is a growing activity in the search of novel single-phase multiferroics that could finally provide distinctive magnetoelectric responses at room temperature, for they would enable a range of potentially disruptive technologies, making use of the ability of controlling polarization with a magnetic field or magnetism with an electric one (for example, voltage-tunable spintronic devices, uncooled magnetic sensors and the long-searched magnetoelectric memory). A very promising novel material concept could be to make use of phase-change phenomena at structural instabilities of a multiferroic state. Indeed, large phase-change magnetoelectric response has been anticipated by a first-principles investigation of the perovskite BiFeO3–BiCoO3 solid solution, specifically at its morphotropic phase boundary between multiferroic polymorphs of rhombohedral and tetragonal symmetries. Here, we report a novel perovskite oxide that belongs to the BiFeO3–BiMnO3–PbTiO3 ternary system, chemically designed to present such multiferroic phase boundary with enhanced ferroelectricity and canted ferromagnetism, which shows distinctive room-temperature magnetoelectric responses.

Mechanosynthesis and analysis of the multiferroicity of new compositions of the BiFeO3–BiMnO3–PbTiO3 ternary system liable to show room-temperature magnetoelectricity.

The ferromagnetic perovskite oxide BiMnO 3 is a highly topical material, and the solid solutions it forms with antiferromagnetic/ferroelectric BiFeO 3 and with ferroelectric PbTiO 3 result in distinctive polar/nonpolar morphotropic phase boundaries (MPBs). The exploitation of such a type of MPBs could be a novel approach to engineer novel multiferroics with phase-change magnetoelectric responses, in addition to ferroelectrics with enhanced electromechanical performance. Here, the interplay among crystal structure, point defects, and multiferroic properties of the BiMnO 3 -BiFeO 3 -PbTiO 3 ternary system at its line of MPBs between polymorphs of tetragonal P4mm (polar) and orthorhombic Pnma (antipolar) symmetries is reported. A strong dependence of the phase coexistence on thermal history is found: phase percentage significantly changes whether the material is quenched or slowly cooled from high temperature. The origin of this phenomenon is investigated with temperature-dependent structural and physical property characterizations. A major role of the complex defect chemistry, where a Bi/Pb-deficiency allows Mn and Fe ions to have a mixed-valence state, in the delicate balance between polymorphs is proposed, and its influence in the magnetic and electric ferroic orders is defined.