Abstract
Heat capacity measurements provide important insights into the energetic, thermodynamic, and magnetic properties of materials. Herein we report the heat capacity of greigite (Fe3S4) from 1.8 to 300 K. Greigite is a magnetic spinel mineral and through a ferromagnetic magnon term, Cfsw = BfswT3/2, ferrimagnetic ordering is observed in the low-temperature heat capacity. Using a set of theoretical fits of the experimental data, we calculate the thermodynamic functions, including the standard entropy (Δ0TSm°). Greigite is important in iron sulfide formation and reaction pathways in environmental, ore-forming, and technological settings and previous work has measured enthalpies (ΔHr°) of formation and decomposition to neighboring phases. In this work, the stability of greigite relative to the elements is demonstrated with a negative Gibbs energy (ΔGr°) of formation and the stability relative to decomposition products of pyrrhotite (FeS1.092) and pyrite (FeS2) is demonstrated with a positive Gibbs energy (ΔGr°) of decomposition. Values of the standard thermodynamic functions Cp,m°, Δ0TSm°, Δ0THm°, andΦm° are tabulated.
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