Formation of an unconventional Ag valence state in Ag2NiO2

TL;DR

This study reveals an unusual +1/2 valence state of silver in Ag2NiO2 caused by strong interlayer interactions, challenging conventional valence expectations and highlighting complex magnetic fluctuations.

Contribution

First principles calculations uncover the origin of the unconventional Ag valence state due to bonding interactions between layers in Ag2NiO2.

Findings

Ag ion exhibits a +1/2 valence state.

Strong bonding-antibonding interactions drive the valence state.

Enhanced specific heat coefficient likely due to spin fluctuations.

Abstract

The Ag ion in the recently synthesized novel material Ag2NiO2 adopts an extremely unusual valency of 1/2, leaving the Ni ion as 3+, rather than the expected 2+. Using first principles calculations, we show that this mysterious subvalent state emerges due to a strong bonding-antibonding interaction between the two Ag layers which drives the lower band beneath the O p complex, eliminating the possibility of a conventional Ag 1+ valence state. The strong renormalization of the specific heat coefficient, gamma, is likely due to strong spin fluctuations that stem from nearly complete compensation of the ferro- (metallic double exchange and the 90 degree superexchange) and antiferromagnetic (conventional superexchange via Ni-O-Ag-O-Ni path) interactions.