Charge Order Superstructure with Integer Iron Valence in Fe2OBO3

TL;DR

This study reveals that Fe2OBO3 exhibits a well-defined ionic charge order with integer Fe valence states, confirmed by multiple experimental techniques, marking it as a clear example of charge ordering in transition metal oxides.

Contribution

The paper provides the first comprehensive experimental evidence of integer Fe valence charge order in Fe2OBO3, combining structural, spectroscopic, and thermodynamic data.

Findings

Charge order onset at 340 K in Fe2OBO3

Doubling of the unit cell at low temperature

Domains with diagonal charge order identified

Abstract

Solution-grown single crystals of Fe2OBO3 were characterized by specific heat, Mossbauer spectroscopy, and x-ray diffraction. A peak in the specific heat at 340 K indicates the onset of charge order. Evidence for a doubling of the unit cell at low temperature is presented. Combining structural refinement of diffraction data and Mossbauer spectra, domains with diagonal charge order are established. Bond-valence-sum analysis indicates integer valence states of the Fe ions in the charge ordered phase, suggesting Fe2OBO3 is the clearest example of ionic charge order so far.