CAREER: The influence of cation substitution on the hydrous phases of the lower mantle

板块构造将水圈与地球深处的水循环连接起来，因为含氢物质被循环进入地球内部。最近在地球深处发现了含有水合相的多个天然钻石包裹体，这是令人信服的证据，表明地球深处的水循环可能比最初认为的更深。这项研究将使用计算模型和实验相结合的方法来评估在地球下地幔条件下被认为稳定的水合相的稳定性和地球物理性质。尽管预计这些都是次要阶段，但下地幔中储氢的潜力仍然很大，因为它约占地球体积的56%。这个项目将资助对早期职业科学家的关键培训，他们将通过学习如何在一个主要是本科生的机构中平衡教学、研究和学生指导而得到指导。该项目的一个补充教育组成部分是开发一个虚拟现实应用程序，该应用程序将帮助地质学本科生发展空间推理技能，特别关注为患有视觉空间缺陷的神经多样性学生培养公平性和包容性。D阶段[MgSi2O4(OH)2]和H阶段[MgSi2O4(OH)2]是致密的水合硅酸镁(DHMS)，预计将在下地幔的氢循环中发挥关键作用。重要的是，Fe和Al的取代对这些相的稳定性和性质有深远的影响。事实上，H相与d-AlOOH和e-FeOOH形成固溶体，形成一个潜在的连续水合储集层，并具有向下稳定到核幔边界的稳定性。该项目将从头计算与高压高温振动光谱和单晶X射线衍射相结合，评估Al、Fe相D相和H相中间组分的地球物理性质，并探索阳离子取代对压力诱导氢键对称化的影响，而压力诱导氢键对称化对体弹性模量及其压力导数有很大影响。第一原理计算将系统地评估阳离子取代如何影响这些相的压力依赖性质和氢调节，为高压实验提供理论框架。结合结晶学和光谱学方法，将提供有关这些相中氢的原子间作用力和成键环境的详细信息，有助于解释为什么这些相在极端压力和温度下是稳定的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Plate tectonics connects the hydrosphere to a water cycle deep in the Earth, as hydrogen-bearing materials are cycled into the planet's interior. The recent discovery of multiple natural diamond inclusions from the deep Earth that contain hydrous phases is compelling evidence that the water cycle of the deep Earth may extend even deeper than was originally believed. This study will use a combination of computational models and experiments to evaluate the stability and geophysical properties of hydrous phases believed to be stable at the conditions of the Earth's lower mantle. Although these are expected to be minor phases, the potential for hydrogen storage in the lower mantle is still considerable, as it comprises approximately 56% of the Earth's volume. This project will fund critical training for an early career scientist who will be guided through learning how to balance teaching, research, and student mentorship at a primarily undergraduate institution. A complementary educational component of this project is to develop a virtual reality application that will help undergraduate geology students develop spatial reasoning skills, with a particular focus on fostering equity and inclusion for neurodiverse students with visual-spatial deficits.Phase D [MgSi2O4(OH)2] and phase H [MgSiO2(OH)2] are dense hydrous magnesium silicates (DHMSs) that are expected to play a key role in the hydrogen cycle of the lower mantle. Importantly, Fe- and Al-substitution has a profound influence on the stability and properties of these phases. In fact, phase H forms a solid solution with d-AlOOH and e-FeOOH, forming a potentially continuous hydrous reservoir with stability down to the core-mantle boundary. This project combines ab initio calculations with high-pressure, high-temperature vibrational spectroscopy and single-crystal X-ray diffraction to evaluate the geophysical properties of intermediate compositions of Al,Fe-bearing phase D and phase H, and to probe how cation substitution affects pressure-induced hydrogen bond symmetrization, which can have a substantial influence on the bulk modulus and its pressure derivative. First principle calculations will systematically evaluate how cation substitution influences the pressure-dependent properties and hydrogen accommodation in these phases, providing a theoretical framework for high-pressure experiments. Combining crystallographic and spectroscopic approaches will provide detailed information on the interatomic forces and bonding environments of hydrogen within these phases, helping explain why these phases are stable at extreme pressures and temperatures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.