Local lattice structure change in $\mathrm{Pr}\mathrm{Ni}{\mathrm{O}}_3$ 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 $\mathrm{Pr}\mathrm{Ni}{\mathrm{O}}_3$ 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 ${}^{16}\mathrm{O}\text{−}{}^{18}\mathrm{O}$ isotopic shift in the temperature at which the XANES exhibits the change attributed to the switching of the local symmetry from orthorhombic to monoclinic.

Figure 1

(Color online) Normalized Ni $K$-edge XANES experimental data at different temperatures above (dashed lines) and below (solid lines) of metal-insulator transition. Quoted temperatures refer to nominal temperatures as explained in the text.

Figure 2

Ni $K$-edge XANES simulation using the average crystallographic structure reported by neutron diffraction in the insulator (solid line) and metallic (dashed line) phases.

Figure 3

Ni $K$-edge XANES simulation in the metallic (dashed line) and insulating (solid line) phases using orthorhombic symmetry and monoclinic symmetry groups respectively (dashed line). Insert: $\mathrm{Ni}p$ density of states as a function of energy, measured from the calculated Fermi level, for the orthorhombic structure (dashed line) and monoclinic structure (solid line).

Figure 4

(Color online) Ni $K$-edge XANES for ${}^{18}\mathrm{O}$ $\mathrm{Pr}\mathrm{Ni}{\mathrm{O}}_3$ at different temperatures above (dashed lines) and below (solid lines) of the metal-insulator transition. Quoted temperatures refer to nominal temperatures as explained in the text.