Browsing by Author "Senyshyn, A"
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- ItemEnergy landscape for Li-ion diffusion in the garnet-type solid electrolyte Li6.5La3Zr1.5Nb0.5O12 (LLZO-Nb)(De Gruyter, 2022-05-24) Strangmüller, S; Avdeev, M; Baran, V; Walke, P; Kirchberger, A; Nilges, T; Senyshyn, AA comprehensive understanding of the nexus of diffusion mechanisms on the atomic scale as well as structural influences on the ionic motion in solid electrolytes is key for further development of high-performing all-solid-state batteries. Therefore, current research not only focuses on the search for innovative materials, but also on the study of diffusion pathways and ion dynamics in ionic conductors. In this context, we report on the extended characterization of the ionic electrolyte Li6.5La3Zr1.5Nb0.5O12 (LLZO-Nb). The commercially available material is analyzed by a combination of powder X-ray (either lab- or synchrotron-based) and neutron diffraction. Details of lithium disorder were obtained from high-resolution neutron diffraction data, from which the ionic transport of Li ions was determined by applying the maximum entropy method in combination with the one-particle potential formalism. © 2022 Walter de Gruyter GmbH
- ItemMagnetic structure and spin correlations in magnetoelectric honeycomb Mn4Ta2O9(American Physical Society, 2018-10-22) Narayanan, N; Senyshyn, A; Mikhailova, D; Faske, T; Lu, T; Liu, Z; Weise, B; Ehrenberg, H; Mole, RA; Hutchison, WD; Fuess, H; McIntyre, GJ; Liu, Y; Yu, DHWe elucidate the magnetic interactions and the role of spin (electron) correlation in determining the ground state of the honeycomb compound Mn4Ta2O9, by neutron powder diffraction, inelastic neutron scattering (INS), specific-heat (CP) measurements, and electronic-structure calculations. The antiferromagnetic long-range order with moments along c occurs at 102 K with strong exchange striction and small anisotropy. It is escribed by the three-dimensional Ising model. Diffuse magnetic scattering has been observed above TN, which is attributed to the two-dimensional spin correlations within the Mn2+ honeycombs. This is confirmed by the calculated exchange constants. INS experiments and spin-wave simulations together with CP measurements reveal two gapped modes on the ab plane, originating from the rotation of the spins away from the easy axis c. The magnetic anisotropy is mainly determined by an electron-correlation-assisted dipole-dipole interaction. This work provides insight into the competing origins of the magnetic anisotropy, which leads to different magnetic ground states in the family of honeycomb compounds. ©2018 American Physical Society
- ItemMagnetic transitions and site-disordered induced weak ferromagnetism in (1-x)BiFeO3-xBaTiO3(American Physical Society, 2014-01-31) Singh, A; Senyshyn, A; Fuess, H; Kennedy, SJ; Pandey, DWe present evidence for weak ferromagnetism in both the rhombohedral and cubic compositions of BF-x BT solid solutions for x < 0.55. Rietveld refinement of nuclear and magnetic structures reveals that the G -type antiferromagnetic ordering of the Fe 3+ magnetic sublattice survives up to x ∼ 0.50. We address the issue of weak ferromagnetism due to spin canting, which is allowed by the symmetry in the R 3c space group but not in the cubic Pm3 ¯ m space group. It is shown that the local symmetry of the average cubic compositions of BF-x BT for 0.35 < x < 0.55 is broken due to off-centering of Bi 3+ in the (1-10) plane and O 2− along the ⟨110⟩ direction from their special Wyckoff positions at (0,0,0) and (1/2,1/2,0), respectively. The local O 2− disorder is shown to be equivalent to local antiferrodistortive rotation, leading to deviation of the Fe 3+ -O 2− -Fe 3+ bond angle from 180° that allows spin canting due to Dzyaloshinskii-Moriya interaction D ⃗ i,j ⋅(S ⃗ i ×S ⃗ j ) , which is otherwise irreconcilable with the ideal cubic symmetry. The magnetization and neutron powder diffraction measurements confirm the absence of magnetic ordering at room temperature for x ≳ 0.55. ©2014 American Physical Society
- ItemThe structural behavior of electrochemically delithiated LixNi0.8Co0.15Al0.05O2 (x<1) battery cathodes(Elsevier, 2023-04-30) Hölderle, T; Monchak, M; Baran, V; Dolotko, O; Bette, S; Mikhailova, D; Voss, A; Avdeev, M; Ehrenberg, H; Müller-Buschbaum, P; Senyshyn, AA full series of variously delithiated LixNi0.8Co0.15Al0.05O2 (NCA) (x < 1) battery cathodes is extracted from cylinder Li-ion batteries of 18650-type, and structural studies of electrode materials are performed ex situ applying high-resolution neutron powder diffraction. A set of structural and microstructural parameters at different state-of-charges (SOC) is gathered from full-profile Rietveld refinements. Accurate cell metrics of the NCA lattice are obtained and compared for both, ex situ and operando modes of data collection. A detailed analysis of lithium occupancies and interatomic distances in the NCA cathode is carried out, revealing a shrinking material response of the NCA structure during delithiation, while the experimental quantification of Li/Ni cation mixing showed an SOC independent behavior. The observed deintercalation driven anisotropic broadening of the Bragg reflections in real-life NCA cathodes were analyzed and assigned to an increasing internal anisotropic microstrain, which is linked to the non-uniform distribution of Li in the structure of NCA, resulting in an unstable and unpredictable performance of LIBs. © 2023 Elsevier B.V.
- ItemSymmetry analysis of the ferroic transitions in the coupled honeycomb system (Fe, Co, Mn)4Ta2O9(Australian Institute of Physics, 2020-02-04) Narayanan, N; Faske, T; Lu, T; Liu, Z; Brennan, M; Hester, JR; Avdeev, M; Senyshyn, A; Mikhailova, D; Ehrenberg, H; Hutchison, WD; Mole, RA; Fuess, H; McIntyre, GJ; Liu, Y; Yu, DHExotic phenomena such as spin liquid, spin-orbital entities, magnetic order induced multiferroicity (type ii) or quantum criticality have recently triggered extensive research on the ground state properties of frustrated magnetic systems. The ground states of these compounds are determined by the coupling of the spin to the orbital, charge and lattice degrees of freedom. One of the extensively investigated lattices is the honeycomb lattice due to the development of the Kitaev model for quantum spin liquids [1-2]. In this work, we are interested in the coupled honeycomb system M4A2O9 (M=Fe, Co and Mn and A=Nb, Ta). All members have two crystallographically distinct M sites, which are in the distorted octahedral oxygen cages. These cages form edge-shared coplanar and corner-shared buckled honeycombs respectively which are interconnected in the perpendicular direction leading to competing exchange paths. The M=Co and Mn members were magnetoelectrics, whereas Fe2Ta2O9 was reported to exhibit both magnetoelectric and (type ii) multiferroic phases depending on the temperature [3-4]. Magnetoelectrics and multiferroics are technically highly relevant with a variety of applications such as MRAMs and field sensors. However, the coupling mechanism is very complicated [5]. Furthermore, due to the group properties of the symmetry analysis methods such as representation analysis and magnetic space groups, the magnetic structure of the Nb counterpart Co4Nb2O9 is controversially discussed. It is therefore apparent that the above discussed diversities of the properties are determined by the magnetic structure and the closely related electronic structure. These can be elucidated by investigating the structure and dynamics of these compounds, which will help to understand the emergence of different ground states and the diverse phase transitions in this family of materials In this work, we systematically investigate the magnetic and electronic structure of the (Fe, Co, Mn)4Ta2O9 system. We combined several different techniques of neutron powder diffraction, inelastic neutron scattering, heat capacity, electronic band structure calculations and spin wave modeling based on linear spin wave theory.
- ItemTwo stage magnetic ordering and spin idle behavior of the coordination polymer Co-3(OH)(2)(C4O4)(2)center dot 3H(2)O determined using neutron diffraction(American Chemical Society, 2011-03-01) Mole, RA; Stride, JA; Henry, PF; Hoelzel, M; Senyshyn, A; Alberola, A; Garcia, CJG; Raithby, PR; Wood, PTWe report the magnetic structure of two of the magnetically ordered phases of Co-3(OH)(2)(C4O4)2 center dot 3H(2)O, a coordination polymer that consists of a triangular framework decorated with anisotropic Co(II) ions. The combination of neutron diffraction experiments and magnetic susceptibility data allows us to identify one phase as displaying spin idle behavior, where only a fraction of the moments order at intermediate temperatures, while at the lowest temperatures the system orders fully. This novel magnetic behavior is discussed within the framework of a simple Hamiltonian and representational analysis and rationalizes this multiphase behavior by considering the combination of frustration and anisotropy. © 2011, American Chemical Society