Review of charge distribution of PbMnO3 Shogo, Wakazaki; Das, Hena; Tatsuru, Yamamoto ...
Meeting Abstracts of the Physical Society of Japan,
2019
Journal Article
The technique of coupling cation ordering with other microscopic degrees of freedom was employed to induce magnetic polar phenomena within the materials belonging to the double perovskite oxide ...family represented by the chemical formula AA′BB′O6, i.e., by considering double cation occupancy at both the 12- and 6-fold oxygen coordinated A- and B- cation sites. Starting from a paraelectric material, La2MnNiO6, that exhibits ferromagnetic behavior near room temperature, we constructed a wide chemical composition space to search for prospective polar magnetic systems. Since we have employed the hybrid improper mechanism of ferroelectricity to induce polar phenomena in these perovskite oxides, ensuring the stability of the cation ordering within certain octahedral rotational pattern was our primary imperative. Hence, we studied the energetics of (1) various A- and B- site cation-ordered phases, (2) cation-disordered phases, (3) various spin configurations, (4) various octahedral rotated structures, and (5) formation of double perovskite compositions with respect to their decomposition into possible stable compositions. On the basis of our study of a series of compositions comprising of transition metal ions from various periods at the B-site, we identify prospective compounds, those are expected to show both polar phenomena with a considerable polar distortion and ferro/ferri-magnetic properties with a considerable high magnetization.
Using first-principles density functional calculations, we study the electronic and magnetic properties of the ferromagnetic insulating double perovskite compound La2NiMnO6, which has been reported ...to exhibit an interesting magnetic field sensitive dielectric anomaly as a function of temperature. Our study reveals the existence of very soft infrared active phonons that couple strongly with spins at the Ni and Mn sites through modification of the superexchange interaction. We suggest that these modes are the origin for the observed dielectric anomaly in La2NiMnO6.
Despite several reports on the surface phase transformations from a layered to a disordered spinel and a rock-salt structure at the surface of the Ni-rich cathodes, the precise structures and ...compositions of these surface phases are unknown. The phenomenon, in itself, is complex and involves the participation of several contributing factors. Of these factors, transition metal (TM) ion migration toward the interior of the particle and hence formation of TM-densified surface layers, triggered by oxygen loss, is thermodynamically probable. Here in this study, we simulate the thermodynamic phase equilibria as a function of TM ion content in the cathode material in the context of lithium nickel oxides, using a combined approach of first-principles density functional calculations, the cluster expansion method, and grand canonical Monte Carlo simulations. We developed a unified lattice Hamiltonian that accommodates not only rock-salt like structures but also topologically different spinel-like structures. Also, our model provides a foundation to investigate metastable cation compositions and kinetics of the phase transformations. Our investigations predict the existence of several Ni-rich phases that were, to date, unknown in the scientific literature. Our simulated phase diagrams at finite temperature show a very low solubility range of the prototype spinel phase. Finally, we find a partially disordered spinel-like phase with far greater solubility that is expected to show very different Li diffusivity compared to that of the prototype spinel structure.
Perovskite-type oxides have been the subject of intense research due to their various fascinating physical properties stemming from their charge degree of freedom. PbFeO3 has an unusual Pb2+ 0.5Pb4+ ...0.5Fe3+O3 charge distribution with a long-ranged ordering of Pb2+ and Pb4+ and two inequivalent Fe3+ sites in a perovskite structure. Combined synchrotron X-ray diffraction and Mössbauer spectroscopy revealed a change to an orthorhombic GdFeO3 structure with a unique Fe3+ site and randomly distributed Pb2+ and Pb4+ at 29.0 GPa, namely, pressure-induced amorphization of Pb2+ and Pb4+. The absence of a charge transfer transition to the Pb2+Fe4+O3 phase, which was expected from the comparison with PbCrO3 and PbCoO3, was verified using ab initio density functional theory calculations in the range of 0–70 GPa.
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