Perovskite BiFeO3 and YMnO3 are both multiferroic materials with distinctive magnetoelectric coupling phenomena. Owing to this, the Y1−xBix Mn1−xFexO3 solid solution seems to be a promising system, though poorly studied. This is due to the metastable nature of the orthorhombic perovskite phase of YMnO3 at ambient pressure, and to the complexity of obtaining pure rhombohedral phases for BiFeO3-rich compositions. In this work, nanocrystalline powders across the whole perovskite system were prepared for the first time by mechanosynthesis in a high-energy planetary mill, avoiding high pressure and temperature routes. Thermal decomposition temperatures were determined, and structural characterization was carried out by X-ray powder diffraction and Raman spectroscopy on thermally treated samples of enhanced crystallinity. Two polymorphic phases with orthorhombic Pnma and rhombohedral R3c h symmetries, and their coexistence over a wide compositional range were found. A gradual evolution of the lattice parameters with the composition was revealed for both phases, which suggests the existence of two continuous solid solutions. Following bibliographic data for BiFeO3, first order ferroic phase transitions were located by differential thermal analysis in compositions with x ≥ 0.9. Furthermore, an orthorhombic-rhombohedral structural evolution across the ferroelectric transition was characterized with temperature-dependent X-ray diffraction.

The perovskite (1-x)YMnO3-xBiFeO3 binary system is very promising because of its multiferroic end members. Nanocrystalline phases have been recently obtained by mechanosynthesis across the system, and the perovskite structural evolution has been described. Two continuous solid solutions with orthorhombic Pnma and rhombohedral R3c symmetries were found, which coexist within a broad compositional interval of 0.5≤x≤0.9. This might be a polar-nonpolar morphotropic phase boundary region, at which strong phase-change magnetoelectric responses can be expected. A major issue is phase decomposition at moderate temperatures that highly complicates ceramic processing. This is required for carrying out a sound electrical characterization and also for their use in devices. We present here the application of Spark Plasma Sintering to the ceramic processing of YMnO3-BiFeO3 phases. This advanced technique, when combined with nanocrystalline powders, allowed densifying phases at reduced processing temperatures and times, so that perovskite decomposition was avoided. Electrical measurements were accomplished, and the response was shown to be mostly dominated by conduction. Nonetheless, the intrinsic dielectric permittivity was obtained, and a distinctive enhancement in the phase coexistence region was revealed. Besides, Rayleigh-type behaviour characteristic of ferroelectrics

Perovskite systems with structurally different multiferroic end members are being extensively investigated, because large phase-change magnetoelectric responses have been anticipated at the morphotropic phase boundaries (MPBs) between polymorphic forms with differentiated ferroic orderings. (1-x) YMnO3-x BiFeO3 is one such system, for which two continuous perovskite solid solutions with rhombohedral R3c and orthorhombic Pnma symmetries are present, and coexist across a wide compositional range. This might be a discontinuous MPB between a non-polar and a polar phase, at which the orthorhombic to rhombohedral transition may be electrically induced with a distinctive magnetic signature. In order to explore this possibility, magnetic properties have been characterized across the whole system, and relationships between perovskite crystal structure and magnetism have been established. Distinctive evolutions within each solid solution are revealed that define a region between x=0.6 and 0.9, where a non-polar orthorhombic ferromagnetic phase coexists with a polar rhombohedral antiferromagnetic one at room temperature.