Stability of the Ni sites across the pressure-induced metallization in   YNiO3
  The local environment of nickel atoms in Y NiO3 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/long range, not in the NiO6 octahedron, whereas the evolution of the near-edge XAS features can be associated to 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 inter-octahedra rearrangement. These outcomes provides evidences of the bandwidth driven nature of the IM transition. 
A. Y. Ramos, C. Piamonteze, H. C. N. Tolentino, O. Bunau, Y. Joly, S.   Grenier, J.-P. Itie, N. E. Massa, J. A. Alonso and M...
cond-mat.str-el