Stability of the local Ni site distortions across pressure-induced metallization in YNiO3
Résumé
The local environment of nickel atoms in YNiO3 across the pressure-induced insulator-to-metal (IM) transition was studied using x-ray absorption spectroscopy (XAS) supported by ab initio calculations. The monotonic contraction of the NiO6 units under applied pressure observed up to 13 GPa stops in a limited pressure domain around 14 GPa, before resuming above 16 GPa. In this narrow pressure range, crystallographic modifications basically occur in the medium to long range, not in the NiO6 octahedron, whereas the evolution of the near-edge XAS features can be associated with metallization. Ab initio calculations show that these features are related to medium-range order, provided that the Ni-O-Ni angle enables a proper overlap of the Ni eg and O 2p orbitals. Metallization is then not directly related to modifications in the average local geometry of the NiO6 units but more likely to an interoctahedral rearrangement. These outcomes provide evidence of the bandwidth-driven nature of the IM transition.
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