Mechanosynthesis of the Whole Y1−xBixMn1−xFexO3 Perovskite System: Structural Characterization and Study of Phase Transitions

Abstract

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.

Magnetic properties across the YMnO3-BiFeO3 system designed for phase-change magnetoelectric response

“…This is certainly the case for BiFeO3 (x=1), which presents G-type antiferromagnetic spin arrangement with a long-range incommensurate cycloidal modulation that emerges at 643 K [11]. Differential thermal analysis (DTA) shows a characteristic reversible thermal effect associated with the antiferromagnetic transition, and analogous thermal effects have been reported for x=0.9, 0.925 and 0.95 at 499, 573 and 616 K, respectively [27]. Transition would then shift towards high temperature with increasing…”

“…Perovskite single-phase powdered samples of fourteen compositions across the whole (1-x) YMnO3-x BiFeO3 binary system, including x=0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.925, 0.95, 0.975 and 1, were mechanosynthesized by high energy planetary milling of a stoichiometric mixture of precursor oxides in tungsten carbide media. Details of mechanical treatments, and the required parameters to attain the mechanosynthesis of the different perovskite compounds can be found elsewhere [27]. Phases were controlled by X-ray powder diffraction (XRD) with a Bruker AXS D8 Advance diffractometer.…”

“…The Cu-Kα doublet (λ = 1.5418 Å) was used in the experiments. Nanocrystalline perovskite phases were obtained for all compositions, which showed a distinctive evolution from a pseudo-orthorhombic symmetry to a pseudo-cubic one as x increased [27]. Sample morphology was monitored with a Philips XL 30 S-FEG scanning electron microscope, and submicron sized agglomerates of very small particles with size between 20 and 25 nm resulted.…”

“…The metastable perovskite orthorhombic phase with Pnma symmetry has been obtained by annealing at high pressure [21], mechanosynthesis in high energy planetary mills [26,27], or in thin form under high epitaxial strain [28]. Perovskite YMnO3 shows an incommensurate antiferromagnetic order that develops at 42 K. Improper ferroelectricity appears at a second magnetic transition at 28 K that has associated a distinctive dielectric anomaly [29,30].…”

“…Recently, we succeeded in obtaining perovskite phases all across the YMnO3-BiFeO3 system, free of secondary phases, by mechanosynthesis, and carried out structural characterizations that revealed the presence of two continuous perovskite solid solutions with orthorhombic Pnma and rhombohedral R3c symmetries, which coexisted in a broad compositional interval [27]. Here,…”