Probe Ferroelectricity by X-ray Absorption Spectroscopy in Molecular Crystal

TL;DR

This study uses X-ray absorption spectroscopy to detect ferroelectricity in croconic acid crystals by identifying spectral signatures associated with proton transfer and symmetry breaking.

Contribution

It demonstrates that X-ray absorption spectroscopy can effectively probe ferroelectricity in organic molecular solids through spectral features linked to hydrogen bonding environments.

Findings

Satellite peak in pre-edge spectrum indicates ferroelectricity.

Spectroscopy signatures differentiate ferroelectric and non-ferroelectric states.

Theoretical simulations match experimental spectra accurately.

Abstract

We carry out X-ray absorption spectroscopy experiment at oxygen K-edge in croconic acid (C5H2O5) crystal as a prototype of ferroelectric organic molecular solid, whose electric polarization is generated by proton transfer. The experimental spectrum is well reproduced by the electron-hole excitation theory simulations from configuration generated by ab initio molecular dynamics simulation. When inversion symmetry is broken in ferroelectric state, the hydrogen bonding environment on the two bonded molecules become inequivalent. Such a difference is sensitively probed by the bound excitation in the pre-edge, which are strongly localized on the excited molecules. Our analysis shows that a satellite peak in the pre-edge will emerge at higher excitation energy which serves as a clear signature of ferroelectricity in the material.