Collinear Jahn–Teller Ordering Induces Monoclinic Distortion in “Defect-Free” LiNiO 2

作者：George Phillips, J. Steele, Farheen N. Sayed, Leonhard Karger, Liam A. V. Nagle‐Cocco, Annalena R. Genreith‐Schriever, Gabriel E. Pérez, David A. Keen, Jürgen Janek, Torsten Brezesinski, Joshua D. Bocarsly, Siân E. Dutton, Clare P. Grey · 发表于：Journal of the American Chemical Society · 年份：2025 · DOI：10.1021/jacs.5c07435 · 被引用次数：9 · 研究领域：Advancements in Battery Materials、Ferroelectric and Piezoelectric Materials、Semiconductor materials and devices

High Resolution Image Download MS PowerPoint Slide Lithium nickel oxide, LiNiO 2 (LNO), and its doped derivatives are promising battery cathode materials with high gravimetric capacity and operating voltages. They are also of interest to the field of quantum magnetism due to the presumed S = 1/2 triangular lattice and associated geometric frustration. However, the tendency for Li/Ni substitutional defects and off-stoichiometry makes fundamental studies challenging. In particular, there is still a discrepancy between the rhombohedral ( R 3̅ m ) bulk structure and the Jahn–Teller (JT) distortions of the NiO 6 octahedra inferred on the basis of local structural probes. Karger et al . ( Chem. Mater. 2023, 35, 648–657) recently used Na/Li ion exchange to synthesize “defect-free” LNO by exploiting the absence of antisite disorder in NaNiO 2 (NNO). Here we characterize the short- and long-range structure of this ion-exchanged material and observe splittings of key Bragg reflections at 100 K in X-ray and neutron diffraction (XRD and NPD), indicative of a monoclinic distortion induced by a cooperative collinear JT distortion, similar to that seen in NNO. Variable temperature XRD reveals a second-order phase transition from the monoclinic ( C 2/ m ) low-temperature structure to a rhombohedral ( R 3̅ m ) structure above ∼400 K. We propose that this collinear JT ordering is also present in solid-state synthesized LNO with the domain size and extent of monoclinic distortion controlled by ...