Short-range charge-order in $R$NiO$_{3}$ perovskites ($R$=Pr,Nd,Eu) probed by X-ray absorption spectroscopy

TL;DR

This study uses X-ray absorption spectroscopy to reveal short-range charge-order and coexistence of two Ni sites in $R$NiO$_{3}$ perovskites, across metal-insulator transitions, enhancing understanding of their electronic and magnetic properties.

Contribution

It provides new evidence of short-range charge-order and Ni site coexistence in $R$NiO$_{3}$, even in the metallic state, offering insights into their conduction and magnetic mechanisms.

Findings

Existence of two Ni sites with different bond lengths.

Charge-order observed in the insulating state.

Coexistence of Ni sites in the metallic state.

Abstract

The short-range organization around Ni atoms in orthorhombic $R$NiO$_{3}$ ($R$=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni K-edge x-ray absorption spectroscopy. Our results demonstrate that two different Ni sites, with different average Ni-O bond lengths, coexist in those orthorhombic compounds and that important modifications in the Ni nearest neighbors environment take place across the metal-insulator transition. We report evidences for the existence of short-range charge-order in the insulating state, as found in the monoclinic compounds. Moreover, our results suggest that the two different Ni sites coexists even in the metallic state. The coexistence of two different Ni sites, independently on the $R$ ion, provides a common ground to describe these compounds and shed new light in the understanding of the phonon-assisted conduction mechanism and unusual antiferromagnetism present in all $R$NiO$_{3}$ compounds.