The local environment of nickel atoms in ${\text{YNiO}}_3$ 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 ${\text{NiO}}_6$ 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 ${\text{NiO}}_6$ 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 $e_g$ and O $2p$ orbitals. Metallization is then not directly related to modifications in the average local geometry of the ${\text{NiO}}_6$ units but more likely to an interoctahedral rearrangement. These outcomes provide evidence of the bandwidth-driven nature of the IM transition.

• Received 20 September 2011

DOI:https://doi.org/10.1103/PhysRevB.85.045102