Van Vleck analysis of angularly distorted octahedra using <i>VanVleckCalculator</i>

Nagle-Cocco, Liam. A. V.; Dutton, Siân E.

doi:10.1107/s1600576723009925

Cited by 5 publications

(1 citation statement)

References 104 publications

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“…For octahedra of purely Q 3 character, which is the case for LiNiO 2 , a rotation of Δϕ = 120° indicates a switching of the tetragonally elongated axis. The van Vleck modes in this study were calculated using the Python package VanVleckCalculator, , assuming orthogonal axes.…”

Section: Theoretical Calculationsmentioning

confidence: 99%

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Genreith-Schriever,

Alexiu,

Phillips

et al. 2024

Chem. Mater.

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The atomistic structure of lithium nickelate (LiNiO 2 ), the parent compound of Ni-rich layered oxide cathodes for Li-ion batteries, continues to elude a comprehensive understanding. The common consensus is that the material exhibits local Jahn−Teller distortions that dynamically reorient, resulting in a time-averaged undistorted R3̅ m structure. Through a combination of ab initio molecular dynamics (AIMD) simulations and variabletemperature X-ray diffraction (VT-XRD), we explore Jahn−Teller distortions in LiNiO 2 as a function of temperature. Static Jahn−Teller distortions are observed at low temperatures (T < 250 K) via AIMD simulations, followed by a broad phase transition that occurs between 250 and 350 K, leading to a highly dynamic, displacive phase at high temperatures (T > 350 K), which does not show the four short and two long bonds characteristic of local Jahn−Teller distortions. These transitions are followed in the AIMD simulations via abrupt changes in the calculated pair distribution function and the bond-length distortion index and in X-ray diffraction via the monoclinic lattice parameter ratio, a mon /b mon , and δ angle, the fit quality of an R3̅ m-based structural refinement, and a peak sharpening of the diffraction peaks on heating, consistent with the loss of distorted domains. Between 250 and 350 K, a mixed-phase regime is found via the AIMD simulations where distorted and undistorted domains coexist. The repeated change between the distorted and undistorted states in this mixed-phase regime allows the Jahn−Teller long axes to change direction. These pseudorotations of the Ni−O long axes are a side effect of the onset of the displacive phase transition. Antisite defects, involving Li ions in the Ni layer and Ni ions in the Li layer, are found to pin the undistorted domains at low temperatures, impeding cooperative ordering at a longer length scale.

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Section: Theoretical Calculationsmentioning

confidence: 99%

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Genreith-Schriever,

Alexiu,

Phillips

et al. 2024

Chem. Mater.

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Spin‐Glass States Generated in a van der Waals Magnet by Alkali‐Ion Intercalation

Khan,

Aw,

Nagle‐Cocco

et al. 2024

Advanced Materials

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Tuning magnetic properties in layered van der Waals (vdW) materials has captured significant attention due to the efficient control of ground states by heterostructuring and external stimuli. Electron doping by electrostatic gating, interfacial charge transfer, and intercalation is particularly effective in manipulating the exchange and spin‐orbit properties, resulting in a control of Curie temperature (TC) and magnetic anisotropy. Here, an uncharted role of intercalation is discovered to generate magnetic frustration. As a model study, Na atoms are intercalated into the vdW gaps of pristine Cr2Ge2Te6 (CGT) where generated magnetic frustration leads to emerging spin‐glass states coexisting with a ferromagnetic order. A series of dynamic magnetic susceptibility measurements/analysis confirms the formation of magnetic clusters representing slow dynamics with a distribution of relaxation times. The intercalation also modifies other macroscopic physical parameters including the significant enhancement of TC from 66 to 240 K and the switching of magnetic easy‐hard axis direction. This study identifies intercalation as a unique route to generate emerging frustrated spin states in simple vdW crystals.

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Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO₂ Cathodes

Sada,

Kmiec,

Manthiram

2024

Angewandte Chemie

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The O‐type layered nickel oxides suffer from undesired co‐operative Jahn‐Teller distortion stemming from Ni3+ ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na+ ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5% divalent (Mg2+) or trivalent (Al3+ or Co3+) ions for Ni3+ to alleviate Na+‐ion ordering and perturb the Jahn‐Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg‐O and Na‐O or Mg‐O‐Na bonding interactions, noting that the ionicity of the Mg‐O bond deshields the electronic cloud of oxygen from Na+ ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO6 octahedra from Jahn‐Teller distortion and a reduced electron density at the interlayer with Mg2+ substitution. Long‐range (operando X‐ray diffraction) and short‐range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg‐substitution results in a high‐capacity retention of ~ 96% even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium‐ion batteries.

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Van Vleck analysis of angularly distorted octahedra using VanVleckCalculator

Cited by 5 publications

References 104 publications

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Spin‐Glass States Generated in a van der Waals Magnet by Alkali‐Ion Intercalation

Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO₂ Cathodes

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Van Vleck analysis of angularly distorted octahedra using VanVleckCalculator

Cited by 5 publications

References 104 publications

Jahn–Teller Distortions and Phase Transitions in LiNiO2: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Jahn–Teller Distortions and Phase Transitions in LiNiO2: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Spin‐Glass States Generated in a van der Waals Magnet by Alkali‐Ion Intercalation

Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO2 Cathodes

Contact Info

Product

Resources

About

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Jahn–Teller Distortions and Phase Transitions in LiNiO₂: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction

Mitigating Sodium Ordering for Enhanced Solid Solution Behavior in Layered NaNiO₂ Cathodes