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

当含氢物质循环进入地球内部时，板块构造将水圈与地球深处的水循环联系起来。最近从地球深处发现的含有水相的多种天然钻石内含物是令人信服的证据，表明地球深处的水循环可能比最初认为的还要深。这项研究将使用计算模型和实验相结合的方法来评估被认为在地球下地幔条件下稳定的水相的稳定性和地球物理特性。虽然这些都是较小的阶段，但下地幔中储氢的潜力仍然相当大，因为它占地球体积的56%左右。该项目将资助一名早期职业科学家的关键培训，该科学家将在一所主要的本科院校学习如何平衡教学、研究和学生指导。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，帮助地质学本科生发展空间推理技能，特别注重培养具有视觉空间缺陷的神经多样性学生的公平性和包容性。D相[MgSi2O4(OH)2]和H相[mgsisio2 (OH)2]是致密的水合硅酸镁（DHMSs），预计在下地幔氢循环中起关键作用。重要的是，铁和铝取代对这些相的稳定性和性能有深远的影响。事实上，H相与d-AlOOH和e-FeOOH形成了固溶体，形成了一个潜在的连续含水储层，其稳定性一直持续到核幔边界。本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，评价含Al、含fe的D相和H相中间成分的地球物理性质，探讨阳离子取代对压力诱导氢键对称的影响，从而对体积模量及其压力导数产生实质性影响。第一性原理计算将系统地评估阳离子取代如何影响这些相中的压力依赖性质和氢容纳，为高压实验提供理论框架。结合晶体学和光谱方法将提供这些相中氢的原子间作用力和键合环境的详细信息，有助于解释为什么这些相在极端压力和温度下是稳定的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.