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arXiv · 2408.01267

Displacive Jahn--Teller transition in NaNiO$_2$

Liam Agostino Vincenzo Nagle-Cocco·Annalena R. Genreith-Schriever·James M. A. Steele·Camilla Tacconis·Joshua D. Bocarsly·Olivier Mathon·Joerg C. Neuefeind·Jue Liu·Christopher A. O'Keefe·Andrew L. Goodwin·Clare P. Grey·John S. O. Evans·Siân E. Dutton
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Abstract

Below its Jahn--Teller transition temperature, $T_\mathrm{JT}$, NaNiO$_2$ has a monoclinic layered structure consisting of alternating layers of edge-sharing NaO$_6$ and Jahn-Teller-distorted NiO$_6$ octahedra. Above $T_\mathrm{JT}$ where NaNiO$_2$ is rhombohedral, diffraction measurements show the absence of a cooperative Jahn-Teller distortion, accompanied by an increase in the unit cell volume. Using neutron total scattering, solid-state Nuclear Magnetic Resonance (NMR), and extended X-ray absorption fine structure (EXAFS) experiments as local probes of the structure we find direct evidence for a displacive, as opposed to order-disorder Jahn-Teller transition at $T_\mathrm{JT}$. This is supported by \textit{ab initio} molecular dynamics (AIMD) simulations. To our knowledge this study is the first to show a displacive Jahn-Teller transition in any material using direct observations with local probe techniques.

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Liam Agostino Vincenzo Nagle-Cocco, Annalena R. Genreith-Schriever, James M. A. Steele, Camilla Tacconis, Joshua D. Bocarsly, Olivier Mathon, Joerg C. Neuefeind, Jue Liu, Christopher A. O'Keefe, Andrew L. Goodwin, Clare P. Grey, John S. O. Evans, Siân E. Dutton. 2024-08-02. Displacive Jahn--Teller transition in NaNiO$_2$. https://arxiv.org/abs/2408.01267

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