Unusual Mott transition associated with charge-order melting in BiNiO${}_3$ under pressure

Abstract

We study the electronic structure, magnetic state, and phase stability of paramagnetic BiNiO${}_3$ near a pressure-induced Mott insulator-to-metal transition (MIT) by employing a combination of density functional and dynamical mean-field theory. We obtain that BiNiO${}_3$ exhibits an anomalous negative-charge-transfer insulating state, characterized by charge disproportionation of the Bi $6s$ states, with Ni${}^{2+}$ ions. Upon a compression of the lattice volume by $\sim$4.8\%, BiNiO${}_3$ is found to make a Mott MIT, accompanied by the change of crystal structure from triclinic $P\bar{1}$ to orthorhombic $Pbnm$. The pressure-induced MIT is associated with the melting of charge disproportionation of the Bi ions, caused by a charge transfer between the Bi $6s$ and O $2p$ states. The Ni sites remain to be Ni${}^{2+}$ across the MIT, which is incompatible with the valence-skipping Ni${}^{2+}$/Ni${}^{3+}$ model. Our results suggest that the pressure-induced change of the crystal structure drives the MIT in BiNiO${}_3$.

5 pages, 4 figures