1 DOI: 10.1002/ ((please add manuscript number)) Article type: Full Paper The Polar/Antipolar Phase Boundary of BiMnO 3 -BiFeO 3 -PbTiO 3 : Interplay among Crystal Structure, Point Defects and Multiferroism Carmen M. Fernández-Posada, Alicia Castro, Jean-Michel Kiat, Florence Porcher, Octavio Peña, Ricardo Jiménez, Miguel Algueró, and Harvey Amorín* Dr. C. M. Fernández-Posada, Prof. A. Castro, Dr. R. Jiménez, Dr. M. Algueró, Dr. H. Amorín Instituto de Ciencia de Materiales de Madrid, CSIC. Cantoblanco, 28049 Madrid, Spain E-mail: hamorin@icmm.csic.es Prof. J.-M. Kiat Laboratoire Structures, Propriétés et Modélisation des Solides, associé au CNRS (UMR 8580), Ecole Centrale Paris, Chatenay-Malabry 92295, France Prof. J.-M. Kiat, Dr. F. Porcher Laboratoire Léon Brillouin, CEA/Saclay, F-91191 Gif-Sur-Yvette Cedex, France Prof. O. Peña Institut des Sciences Chimiques de Rennes, associé au CNRS (UMR 6226), Université de Rennes 1, Rennes 35042, France Keywords: multiferroics; perovskites; point defects; morphotropic phase boundaries; structure-property relationships A highly topical material is the ferromagnetic perovskite oxide BiMnO 3 , and also the solid solutions it forms with antiferromagnetic/ferroelectric BiFeO 3 and with ferroelectric PbTiO 3 that result in distinctive polar/non-polar morphotropic phase boundaries (MPBs). The exploitation of such 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. We report 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. A strong dependence of the phase coexistence on thermal history was found, so as 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