Fig. 2: Schematic of the electronic and structural disproportionation in the insulating state in rare-earth nickelates.
From: Quantifying the role of the lattice in metal–insulator phase transitions
NiO6 octahedra disproportionate electronically and structurally in a three-dimensional checkerboard pattern in RNiO3 metal–insulator transition compounds, with R a rare-earth. In the low-energy model of refs. 4,6, the Ni ions corresponding to the larger octahedra have 1e− \(+\frac{{{\Delta }}N}{2}\) electrons (dark blue) in their eg shell, while those corresponding to the smaller one (light blue) have 1e− \(-\frac{{{\Delta }}N}{2}\). The difference in average bond lengths defines Q for the nickelate materials. Red circles correspond to oxygen atoms, while the green arrow is a measure of the oxygen displacement along the Ni-Ni direction.
