Abstract
The insulator–bad metal transition observed in Jahn–Teller (JT) magnets orthonickelate RNiO \(_{3}\) (R = rare earth or yttrium Y) is considered a canonical example of the Mott transition described within the \(U\) – \(t\) Hubbard model. In contrast to the traditional approach, we associate the Mott transition with the destruction of the charge-disproportionated (CD) phase of nickelates, which is typical for JT magnets, being unstable with respect to charge transfer. Within the charge triplet model proposed to describe the CD phase, we consider the main interactions responsible both for the Mott transition and all main features of electronic structure and phase diagrams of nickelates. The simplest atomic limit, the \(U\) – \(V\) model, is tackled in the effective field approximation, which allows us to explain the principal features of the insulator–bad metal transition in nickelates.
