Browsing by Author "Ahn, D"

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    Magnetic transitions in the chiral armchair-kagome system Mn2Sb2O7
    (American Physical Society, 2017-01-20) Peets, DC; Sim, H; Choi, S; Avdeev, M; Lee, S; Kim, SJ; Kang, H; Ahn, D; Park, JG
    The competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. Mn2Sb2O7 forms in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. Mn2Sb2O7 exhibits two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the P3121 space group, Mn2Sb2O7 actually crystallizes in P2, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional “armchair-kagome” lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems. ©2017 American Physical Society
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    Unravelling the nature of the intrinsic complex structure of binary‐phase Na‐layered oxides
    (Wiley, 2022-07) Paidi, AK; Park, WB; Ramakrishnan, P; Lee, SH; Lee, JW; Lee, KS; Ahn, H; Liu, T; Gim, J; Avdeev, M; Pyo, M; Sohn, JI; Amine, K; Sohn, KS; Shin, TJ; Ahn, D; Lu, J
    The layered sodium transition metal oxide, NaTMO2 (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium‐ion batteries (SIBs). Herein, an in‐depth phase analysis of developed Na1−xTMO2 cathode materials, Na0.76Ni0.20Fe0.40Mn0.40O2 with P2‐ and O3‐type phases (NFMO‐P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed‐phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first‐principles calculations support the evidence of the formation of a binary NFMO‐P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O′3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P‐ and O‐type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5–4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high‐voltage cathode materials for SIBs. © 1999-2024 John Wiley & Sons