Ground-state valency and spin configuration of the Ni-ions in nickelates

TL;DR

This study uses advanced ab initio methods to analyze the electronic structure and valency states of nickel ions in nickelates, revealing how impurity substitution affects their spin states and orbital ordering.

Contribution

It provides a detailed theoretical analysis of ground-state valency and spin configurations in nickelates, highlighting impurity effects on electronic and magnetic properties.

Findings

LiNiO2 and NaNiO2 are insulators with Ni3+ low spin state.

Impurity substitution causes Ni ions to switch from Ni3+ to Ni2+ states.

Ni2+ impurities disrupt long-range orbital ordering in LiNiO2.

Abstract

The ab initio self-interaction-corrected local-spin-density approximation is used to study the electronic structure of both stoichiometric and non-stoichiometric nickelates. From total energy considerations it emerges that, in their ground-state, both LiNiO2 and NaNiO2 are insulators, with the Ni ion in the Ni3+ low spin state (6t2g 1eg) configuration. It is established that a substitution of a number of Li/Na atoms by divalent impurities drives an equivalent number of Ni ions in the NiO2 layers from the JT-active trivalent low-spin state to the JT-inactive divalent state. We describe how the observed considerable di_erences between LiNiO2 and NaNiO2 can be explained through the creation of Ni2+ impurities in LiNiO2. The indications are that the random distribution of the Ni2+ impurities might be responsible for the destruction of the long-range orbital ordering in LiNiO2.