Temperature-dependent Behaviour of Jahn−Teller Distortions in Defect-free LiNiO2

This work aims to investigate the nature of Jahn−Teller (JT) distortions in candidate lithium-ion cathode material lithium nickel oxide, LiNiO2 (LNO). LNO typically crystallises in the rhombohedral space group R-3m, where the threefold symmetry precludes a macroscopic JT distortion despite the low-spin d7 electronic configuration of the Ni3+. Previous neutron PDF measurements confirm local JT distortions in this material at low temperatures but their exact nature—whether they are dynamic or static, and in turn their spatial distribution—remains an open question. Our previous AIMD calculations indicate the important role that point defects play in the behaviour and spatial coherence of the JT distortions, pinning the undistorted domains. We have an ion-exchanged LNO sample, synthesised from the sodium analogue NaNiO2 (NNO), which retains the defect-free property of the NNO. A deeper understanding of the JT distortions and their temperature sensitivity in a sample with no defects will improve our understanding of the interplay between orbital, magnetic and elastic degrees of freedom in LNO, and act as a starting point for understanding the wider influence of point-defects in LNO as well as the structure of the material at different stages of lithiation.