Zigzag chain order of ${\mathrm{LiVSe}}_{2}$ developing away from the vanadium trimer phase transition boundary

Zigzag chain order of ${LiVSe}_{2}$ developing away from the vanadium trimer phase transition boundary

K. Kojima, N. Katayama, K. Sugimoto, N. Hirao, Y. Ohta, and H. Sawa

Phys. Rev. B 108, 094107 – Published 15 September 2023

Abstract

The phenomenon of self-assembly of constituent elements to form molecules at low temperatures appears ubiquitously in transition metal compounds with orbital degrees of freedom. Recent progress in local structure studies using synchrotron radiation x rays is shifting the interest in structural studies in such molecule-forming systems from the low-temperature ordered phase to the short-range order that appears like a precursor at high temperatures. In this study, we discuss both experimentally and theoretically the relationship between the trimer structure that appears in the layered $LiV X_{2} (X$ = O, S, Se) system with a two-dimensional triangular lattice of vanadium and the zigzag chainlike local structure that appears near the phase transition boundary where molecular formation occurs. The vanadium trimerization that persistently appears in both low-temperature phases of ${LiVO}_{2}$ and ${LiVS}_{2}$ disappears in ${LiVSe}_{2}$ , and a regular triangular lattice is thought to be realized in ${LiVSe}_{2}$ , but this study reveals that the zigzag chain local distortion appears with a finite correlation length. These zigzag chain state local distortions are similar to the motif of local distortions in the high-temperature phase of ${LiVS}_{2}$ , indicating that the local distortions are persistent away from the trimer phase transition boundary. On the other hand, it is concluded that the zigzag chain order appearing in ${LiVSe}_{2}$ is more stable than that in ${LiVS}_{2}$ in terms of the temperature variation of atomic displacement and correlation length. The zigzag chain order is considered to be competitive with the trimer order appearing in the $LiV X_{2}$ system. In this paper, we discuss the similarities and differences between the parameters that stabilize these electronic phases and the local distortions that appear in other molecular formation systems.

Received 21 March 2023
Revised 29 June 2023
Accepted 5 September 2023

DOI:https://doi.org/10.1103/PhysRevB.108.094107

Physics Subject Headings (PhySH)

High-pressure studies Phase diagrams Phase transitions Structural properties

Layered crystals Strongly correlated systems Triangular lattice

X-ray diffraction X-ray powder diffraction

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

K. Kojima ¹, N. Katayama^1,*, K. Sugimoto ², N. Hirao³, Y. Ohta ⁴, and H. Sawa¹

¹Department of Applied Physics, Nagoya University, Aichi 464-8603, Japan
²Department of Physics, Keio University, Kanagawa 223-8522, Japan
³Diffraction and Scattering Division, Center for Synchrotron Radiation, Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan
⁴Department of Physics, Chiba University, Chiba 263-8522, Japan

^*Corresponding author: katayama.naoyuki.m5@f.mail.nagoya-u.ac.jp

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Vol. 108, Iss. 9 — 1 September 2023

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Figure 1
Phase diagram of the $LiV X_{2}$ system. Although the classification of each phase has been shown in previous studies [9, 28], our study reveals that the zigzag chain state shown in green appears more stable in ${LiVSe}_{2}$ , which is farther from the trimer phase boundary compared to ${LiVS}_{2}$ . The different colored dotted lines on the inset figures indicate different V-V distances.
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Figure 2
(a), (b) Rietveld analysis at 100 K for assuming (a) a triangular lattice and (b) a zigzag chain structure. The insets show the area of the green box. The green ticks are the peak positions of the structure used for fitting, and the gray ticks are for impurity ${Li}_{2} Se$ .
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Figure 3
(a) Temperature dependence of the x-ray diffraction data of ${LiVSe}_{2}$ obtained at ambient pressure. The indices of each peak listed in the figure assume a triangular lattice structure. (b) Intensity ratios of the peaks $\bar{\frac{1}{2}} 12 + \frac{1}{2} 10$ (blue) and $\frac{1}{2} 03 + \frac{1}{2} 0 \bar{3}$ (red) in ${LiVSe}_{2}$ and ${LiVS}_{2}$ (Ref. [28]) to the 001 fundamental peak. The values due to ${LiVS}_{2}$ are so small that they are enlarged and shown on the right. (c) Temperature dependence of the V-V distance obtained by Rietveld analysis. The colors plotted for each interatomic distance correspond to the dotted lines shown in the structure diagram to the right of the graph.
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Figure 4
(a) The RDFs by XAFS measurements on $LiV X_{2}$ . (b) Results of DSC measurements in ${LiVSe}_{2}$ and reference ${LiVS}_{2}$ ; results of DSC measurements in ${LiVS}_{2}$ are equal to those reported in previous studies [28].
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Figure 5
(a) Partial-DOSs of ${LiVS}_{2}$ (upper) and ${LiVSe}_{2}$ (lower) assuming a triangular lattice structure. (b) Partial DOSs of ${LiVS}_{2}$ (upper) and ${LiVSe}_{2}$ (lower) assuming a zigzag chain structure. (c) Shapes of Fermi surfaces for ${LiVS}_{2}$ (upper) and ${LiVSe}_{2}$ (lower) with a triangular lattice structure. The figures of ${LiVS}_{2}$ are equal to those shown in the previous study [28]. (d) Relationship between $d_{x y}, d_{y z}$ , and $d_{z x}$ orbitals. Electrons occupy $\frac{1}{3}$ of each orbital. (e) Zigzag chain formation due to the change of filling by charge transfer.
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Figure 6
(a) Pressure dependence of diffraction data. The figure shows diffraction data from ambient pressure to 40 GPa in increments of about 5 GPa. An enlarged view of the low-angle data is shown below. (b) Pressure dependencies of the lattice parameters and $c / a$ at 8 K. $c / a$ for ${VSe}_{2}$ is taken from Sereika $e t a l .$ [44] as a reference. (c) Pressure dependence of the estimated in-plane V-V distance. (d) Temperature dependence of averaged V-S distance in ${LiVS}_{2}$ .
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Physical Review B

covering condensed matter and materials physics

Zigzag chain order of ${LiVSe}_{2}$ developing away from the vanadium trimer phase transition boundary

K. Kojima, N. Katayama, K. Sugimoto, N. Hirao, Y. Ohta, and H. Sawa

Phys. Rev. B 108, 094107 – Published 15 September 2023

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Physical Review B

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Zigzag chain order of LiVSe2 developing away from the vanadium trimer phase transition boundary

K. Kojima, N. Katayama, K. Sugimoto, N. Hirao, Y. Ohta, and H. Sawa

Phys. Rev. B 108, 094107 – Published 15 September 2023

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Zigzag chain order of ${LiVSe}_{2}$ developing away from the vanadium trimer phase transition boundary