Charge transfer in FeOCl intercalation compounds and its pressure dependence: An x-ray spectroscopic study

TL;DR

This study investigates charge transfer mechanisms in FeOCl intercalation compounds using x-ray spectroscopy, revealing that intercalation involves significant Fe reduction and that pressure enhances conductivity.

Contribution

The paper provides the first detailed spectroscopic analysis distinguishing electronic and structural changes during intercalation, showing charge transfer involves about 25% Fe reduction and increases with pressure.

Findings

Approximately 25% of Fe sites are reduced to Fe2+ during intercalation.

Charge transfer occurs on the same timescale as the Mossbauer effect.

Pressure increases Fe2+ fraction, suggesting enhanced conductivity.

Abstract

We present a study of charge transfer in Na-intercalated FeOCl and polyaniline-intercalated FeOCl using high-resolution x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Fe-K edge. By comparing the experimental data with ab-initio simulations, we are able to unambiguously distinguish the spectral changes which appear due to intercalation into those of electronic origin and those of structural origin. For both systems, we find that about 25% of the Fe sites are reduced to Fe2+ via charge transfer between FeOCl and the intercalate. This is about twice as large as the Fe2+ fraction reported in studies using Mossbauer spectroscopy. This discrepancy is ascribed to the fact that the charge transfer occurs on the same time scale as the Mossbauer effect itself. Our result suggests that every intercalated atom or molecule is involved in the charge-transfer process, thus making this process a prerequisite for intercalation. The Fe2+ fraction is found to increase with pressure for polyaniline-FeOCl, hinting at an enhancement of the conductivity in the FeOCl intercalation compounds under pressure.