Evolution of Ni local structure in NdNiO3 perovskite across the metal-insulator transition

NdNiO3 presents a metal-insulator (MI) transition at 200K with decreasing temperature. This system was characterized by neutron diffraction as orthorhombic with a very symmetric Ni site and almost no modi. cation at the NiO6 octahedra is observed across the transition. We carried out EXAFS measurements on NdNiO3 from room temperature down to 10 K, crossing the MI transition and observed important local modi. cations at the Ni site. The phase derivative method shows that there are distorted Ni sites, with at least two different Ni-O distances, along all the temperature range measured. The modi. cation across the MI transition concerns the increasing of the distorted phase. This hypothesis is sustained by the behavior of the Debye-Waller factor (sigma(2)) with temperature. With decreasing temperature, when the sample is around T-MI sigma(2) rapidly increases due to the growing amount of distorted sites. These results give basis for a discussion in terms of a percolative transition.