The ferromagnetic perovskite oxide BiMnO3 is a highly topical material, and the solid solutions it forms with antiferromagnetic/ferroelectric BiFeO3
and with ferroelectric PbTiO3
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 BiMnO3
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.
Adv. Func. Mater. 2018
Dynamical mechanical analysis. Young's modulus (Y) as a function of temperature at 40 Hz for a,b) Bi0.4Pb0.6Mn0.4Ti0.6O3and c,d) Bi0.47Pb0.53Fe0.17Mn0.3Ti0.53O3ceramic bars, both with quenching treatment from 750 °C, and measured during two successive heating/cooling cycles. Insets (a,b) show mechanical losses (tan δ) as a function of temperature. e) Successive thermal cycles between room temperature and an increasingly higher temperature for the Bi0.47Pb0.53Fe0.17Mn0.3Ti0.53O3ceramic with quenching.