Local lattice structure change in PrNiO3 across the metal-insulator transition:: X-ray absorption near-edge structure spectroscopy and ab initio calculations

X-ray absorption near edge structure (XANES) measurements at the Ni K edge of PrNiO3 across the metal insulator transition show that a change in the local lattice structure accompanies such transition. Theoretical calculations of the XANES show that the observed features of the spectra are consistent with the orthorhombic structure, reported by neutron diffraction, in the metallic phase. However, for the insulating phase, a change in the local symmetry, consistent with a monoclinic structure, is required to reproduce the spectra. This local symmetry change yields to two nickel sites with different local environment and implies a strong electron-lattice interaction at the local level. This claim is also supported by the observation of a O-16-O-18 isotopic shift in the temperature at which the XANES exhibits the change attributed to the switching of the local symmetry from orthorhombic to monoclinic.