TY - JOUR

T1 - Thermal behavior of römerite over a Mars surface relevant temperature range: single crystal X-ray and powder X-ray crystallography and magnetic properties

AU - Борисов, Артем Сергеевич

AU - Абдулина, Вероника Ринатовна

AU - Сийдра, Олег Иоханнесович

AU - Гинга, Виктория Александровна

AU - Цирлин, Александр

AU - Хольцхейд , A.

AU - Zapfe, Annika

AU - Setzer, Annette

PY - 2025/8/15

Y1 - 2025/8/15

N2 - A number of hydrous iron sulfate minerals have been detected on the surface of Mars under extraterrestrial conditions. Nonetheless, certain inquiries regarding the properties and phase evolution of hydrous iron sulfate minerals remain unresolved and subject to debate at present. In our research, the behavior of römerite, Fe2+Fe3+2(SO4)4(H2O)14, was examined by utilizing in situ single-crystal and powder X-ray diffraction while simultaneously acquiring data upon heating. Römerite is stable under low-vacuum conditions. It exhibits a significant negative thermal expansion in the α33 direction throughout the entire temperature range from -173 to 77°C and on up to decomposition. There is a cooperative interaction between the rotation of the sulfate tetrahedra in the [Fe3+(SO4)2(H2O)4]-clusters and the features of the hydrogen-bond system that determines the thermal expansion of römerite. The structure of römerite shows that the sulfate tetrahedra are the most rigid complexes, followed by the Fe23+O2(H2O)4 octahedra, and the Fe12+(H2O)6 octahedra are the most flexible. High-temperature powder X-ray diffraction, thermogravimetry and differential scanning calorimetry were used to determine the phase transformations and the eventual decomposition of römerite at higher temperatures up to 740°C. The decomposition of römerite at 60°C is followed by an amorphization, a transformation into a mikasaite-like phase at ∼275°C and a further decomposition into a hematite-like phase above 550°C, associated with the high-temperature form of magnetite, Fe3O4, above 575°C. The magnetic behavior of römerite reveals weak interactions between the Fe2+and Fe3+centers, in line with the large spatial separation between these ions.

AB - A number of hydrous iron sulfate minerals have been detected on the surface of Mars under extraterrestrial conditions. Nonetheless, certain inquiries regarding the properties and phase evolution of hydrous iron sulfate minerals remain unresolved and subject to debate at present. In our research, the behavior of römerite, Fe2+Fe3+2(SO4)4(H2O)14, was examined by utilizing in situ single-crystal and powder X-ray diffraction while simultaneously acquiring data upon heating. Römerite is stable under low-vacuum conditions. It exhibits a significant negative thermal expansion in the α33 direction throughout the entire temperature range from -173 to 77°C and on up to decomposition. There is a cooperative interaction between the rotation of the sulfate tetrahedra in the [Fe3+(SO4)2(H2O)4]-clusters and the features of the hydrogen-bond system that determines the thermal expansion of römerite. The structure of römerite shows that the sulfate tetrahedra are the most rigid complexes, followed by the Fe23+O2(H2O)4 octahedra, and the Fe12+(H2O)6 octahedra are the most flexible. High-temperature powder X-ray diffraction, thermogravimetry and differential scanning calorimetry were used to determine the phase transformations and the eventual decomposition of römerite at higher temperatures up to 740°C. The decomposition of römerite at 60°C is followed by an amorphization, a transformation into a mikasaite-like phase at ∼275°C and a further decomposition into a hematite-like phase above 550°C, associated with the high-temperature form of magnetite, Fe3O4, above 575°C. The magnetic behavior of römerite reveals weak interactions between the Fe2+and Fe3+centers, in line with the large spatial separation between these ions.

KW - Mars

KW - iron compounds

KW - magnetism

KW - non-ambient powder X-ray diffraction

KW - non-ambient single-crystal X-ray diffraction

KW - römerite

KW - sulfates

KW - thermal analysis

KW - thermal expansion

UR - https://www.mendeley.com/catalogue/9eef2dc4-7dec-3f83-b9ed-42f2b4266acd/

U2 - 10.1107/s1600576725002572

DO - 10.1107/s1600576725002572

M3 - Article

VL - 58

SP - 822

EP - 831

JO - Journal of Applied Crystallography

JF - Journal of Applied Crystallography

SN - 0021-8898

IS - Pt 3

ER -