Temperature dependent Resonant X-ray Inelastic Scattering at Ni L3-edge for NaNiO2 and LiNiO2

TL;DR

This study uses temperature-dependent Resonant X-ray Inelastic Scattering at the Ni L3-edge to investigate the local electronic and atomic structures of NaNiO2 and LiNiO2, revealing distinct phase transition behaviors related to Jahn-Teller distortion.

Contribution

It provides new temperature-resolved RIXS data on NaNiO2 and LiNiO2, highlighting differences in their structural phase transitions and electronic responses, aiding understanding of their atomic structures.

Findings

NaNiO2 shows spectral changes indicating Jahn-Teller distortion loss at phase transition.

LiNiO2 exhibits minor spectral modifications, suggesting stable local structure.

The dataset serves as a resource for developing advanced theoretical models.

Abstract

LiNiO2 is a promising cathode material for Li-ion battery but its atomic and electronic structure is under debate. Indeed, two sets of Ni-O distances are identified from local structural probes that are related with either Jahn-Teller distortion or bond disproportionation of NiO6 octahedra. Moreover, LiNiO2 undergoes a monoclinic to rhombohedral transition at 200 K which origin is still unclear. On the other hand, isostructural NaNiO2 shows differences from LiNiO2, as it is a well-known Jahn-Teller distorted system, and it undergoes monoclinic to rhombohedral transition at 500 K associated to the loss of the Jahn-Teller distortion. To understand better these differences, we report here Ni L3-edge Resonant inelastic X-ray scattering experiments on LiNiO2 and NaNiO2 at different temperatures (25 to 520 K) and follow the spectral changes below and above the phase transition temperatures. The observed RIXS spectra and the mapping indicate strong spectral changes for NaNiO2 confirming the disappearance of Jahn-Teller distortion during phase transition while the changes are minor for LiNiO2 suggesting very few modifications in the local structure. Theoretical simulations of RIXS spectra are required for further understanding, however, we believe that the reported dataset can be a crucial resource for developing advanced simulations that are essential to deepening our understanding of the atomic and electronic structure of these nickelates.