Low-temperature crystallography and vibrational properties of rozenite (FeSO₄·4H₂O), a candidate mineral component of the polyhydrated sulfate deposits on Mars

Rozenite (FeSO₄·4H₂O) is a candidate mineral component of the polyhydrated sulfate deposits on the surface and in the subsurface of Mars. In order to better understand its behavior at temperature conditions prevailing on the martian surface and aid its identification in ongoing and future Rover missions we have carried out a combined experimental and computational study of the mineral's structure and properties. We collected neutron powder diffraction data at temperatures ranging from 21 – 290 K, room temperature synchrotron X-ray data and Raman spectra. Moreover, first-principles calculations of the vibrational properties of rozenite were carried out to aid the interpretation of the Raman spectrum. In this work, we demonstrated how combining Raman spectroscopy and X-ray diffraction of the same sample material sealed inside a capillary with complementary first principles calculations yields accurate reference Raman spectra. This workflow enables the construction of a reliable Raman spectroscopic database for planetary exploration, which will be invaluable to shed light on the geological past as well as in identifying resources for the future colonization of planetary bodies throughout the solar system. In this dataset, the self-consistent DFT+U as well as Γ-point phonon calculations, that were compared to the experimentally determined frequencies of the Raman-active modes, are reported, whereas the experimental data was submitted to crystallographic data-bases (i.e., CCSD and ICSD).