Roberts Dennice M, Landin Alyssa R, Ritter Timothy G, Eaves Joel D, Stoldt Conrad R
Department of Mechanical Engineering, University of Colorado Boulder, Boulder, Colorado, 80309, United States.
Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado, 80309, United States.
Sci Rep. 2018 Apr 26;8(1):6591. doi: 10.1038/s41598-018-24739-8.
Solids composed of iron and sulfur are earth abundant and nontoxic, and can exhibit interesting and technologically important optical, electronic, and magnetic phenomena. However, the iron-sulfur (Fe-S) phase diagram is congested in regions of slight non-stoichiometric iron vacancies, and even when the iron atomic composition changes by even a few percent at standard temperature and pressure, there are myriad stable crystal phases that form with qualitatively different electronic properties. Here, we synthesized and characterized nanocrystals of the pyrrhotite-4M structure (FeS) in an anhydrous oleylamine solvent. Upon heating from 140 °C to 180 °C, the solid sequentially transformed into two kinetically trapped FeS intermediate phases before reaching the pyrrhotite-4M final product. Finally, we assessed the effects of iron vacancies using the stoichiometric end-member, troilite, as a reference system. Density functional theory calculations show that iron vacancies in troilite shift the structure from hexagonal FeS to a monoclinic structure, similar to crystal structures of pyrrhotites, and suggest that this iron deficient troilite may be a stable intermediate between the two crystal structures. The calculations predict that defects also close the band gap in iron deficient troilite.
由铁和硫组成的固体在地球上储量丰富且无毒，并且能够展现出有趣且具有重要技术意义的光学、电子和磁学现象。然而，在存在少量非化学计量比铁空位的区域，铁 - 硫（Fe - S）相图较为复杂，即便在标准温度和压力下铁原子组成仅变化百分之几，也会形成大量具有性质迥异电子特性的稳定晶相。在此，我们在无水油胺溶剂中合成并表征了磁黄铁矿 - 4M结构（FeS）的纳米晶体。从140°C加热至180°C时，该固体在达到磁黄铁矿 - 4M最终产物之前，依次转变为两个动力学捕获的FeS中间相。最后，我们以化学计量比端元矿物陨硫铁作为参考体系，评估了铁空位的影响。密度泛函理论计算表明，陨硫铁中的铁空位使结构从六方FeS转变为单斜结构，类似于磁黄铁矿的晶体结构，并表明这种缺铁陨硫铁可能是这两种晶体结构之间的稳定中间体。计算预测缺陷也会使缺铁陨硫铁的带隙变窄。
