The optical properties of magnetite at room temperature were studied by infrared reflectivity measurements as a function of pressure up to 8 GPa. The optical conductivity spectrum consists of a Drude term, two sharp phonon modes, a far-infrared band at around 600 cm−1, and a pronounced mid-infrared absorption band. With increasing pressure both absorption bands shift to lower frequencies and the phonon modes harden in a linear fashion. Based on the shape of the MIR band, the temperature dependence of the dc transport data, and the occurrence of the far-infrared band in the optical conductivity spectrum the polaronic coupling strength in magnetite at room temperature should be classified as intermediate. For the lower-energy phonon mode an abrupt increase of the linear pressure coefficient occurs at around 6 GPa, which could be attributed to minor alterations of the charge distribution among the different Fe sites.
@article{arxiv.1202.4431,
title = {Polaron physics and crossover transition in magnetite probed by pressure-dependent infrared spectroscopy},
author = {J. Ebad-Allah and L. Baldassarre and M. Sing and R. Claessen and V. A. M. Brabers and C. A. Kuntscher},
journal= {arXiv preprint arXiv:1202.4431},
year = {2018}
}