Some Unresolved Problems in the Structural Chemistry of the "FeS" System

铁-硫体系中化合物的结构化学和相变行为在从地核到地壳的环境中非常重要，例如，从Mackinawite(FeS)形成黄铁矿(FeS)是几个地球化学循环中的关键过程。虽然许多对行星表面和内部至关重要的阶段的结构是已知的，但重大问题仍然存在。其中包括解决关于相图、晶体结构(核和电子)以及化学计量比接近FeS的化合物之间的相变机制的相互矛盾的建议。这项基金资助的研究将集中在以下关键问题上：1)高温高压下FES采用的结构是什么？在中等温度和压力下的结构变化报告将使用钻石砧座高压室和石溪大容量高压装置上新安装的探测器系统进行研究。2)高压下中间磁结构的性质是什么？3)当FeS在低温好氧或厌氧环境中析出时，促进稳定性的决定因素是什么，即向黄铁矿或其他竞争相的转变？这些问题是利用原位技术解决的，这种技术复制了与地球环境相关的条件。该项目的一部分依赖于美国和英国的中子和同步加速器X射线源，这些现场实验将在那里进行。

EAR-9909145PariseThe structural chemistry and phase transformation behavior of compounds in the iron-sulfur system are important in settings from the Earth's core to crust where, for example, pyrite (FeS2) formation from mackinawite (FeS) is a key process in several geochemical cycles. While the structures of many of the phases of importance to planetary surfaces and interiors are known, significant questions remain. These include resolution of conflicting proposals for phase diagrams, crystal structures (nuclear and electronic) and the mechanisms of phase transformations between the compounds with stoichiometry close to FeS. The research funded by this grant will concentrate on the following key questions: 1) what are the structures adopted by FeS at high temperature and pressure? Reports of structural changes at intermediate temperatures and pressures will be studied using diamond anvil high pressure cells and a newly installed detector system on the Stony Brook large volume high pressure device. 2) What is the nature of the intermediate magnetic structure at high pressure? 3) When FeS is precipitated in low temperature aerobic or anaerobic environments, what are the determining factors promoting stability, the transformation to pyrite, or to other competing phases? These questions are addressed using in situ techniques, which replicate conditions of relevance to earth environments. Parts of this project rely on neutron and synchrotron X-ray sources in the US and in the UK, where these in situ experiments will be carried out.