Evidence of the isoelectronic character of F doping in SmFeAsO(1-x)F(x): a first-principles investigation

TL;DR

This study uses first-principles calculations to show that fluorine doping in SmFeAsO does not alter charge balance or band structure significantly, with charge compensation occurring via Sm oxidation state change.

Contribution

It reveals that F-doping in SmFeAsO is isoelectronic and involves Sm oxidation state change, challenging previous assumptions about charge doping effects.

Findings

F-doping does not change charge balance or band structure significantly.

Charge compensation occurs through Sm oxidation state change from 3+ to 2+.

F-doping's effect is similar in paramagnetic and antiferromagnetic phases.

Abstract

We study the electronic structure of the SmFeAsO(1-x)F(x) alloy by means of first-principle calculations. We find that, contrary to common believe, F-doping does not change the charge balance between electrons and holes free-carriers in SmFeAsO(1-x)F(x). For energies within a narrow energy range across E_F, the effect of F-doping on the band structure dispersion is tiny in both the paramagnetic and stripe antiferromagnetic phase. The charge balance between the conducting FeAs-layer and the SmO(1-x)F(x) charge reservoir layer is not influenced by the compositional change. The additional charge carried by fluorine, with respect to the oxygen, is compensated by a change in the oxidation state of the Sm ion from 3+ to 2+. A comparison with the SmFe(1-x)Co(x)AsO system shows that such charge compensation by the Sm ion is not shared by donors substituting at the Fe site.