Hydrogen Incorporation in Rutile- and Perovskite-Structured Minerals and Their Analogues

Citation

Palfey, William Richard (2024) Hydrogen Incorporation in Rutile- and Perovskite-Structured Minerals and Their Analogues. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nbyx-6446. https://resolver.caltech.edu/CaltechTHESIS:06032024-221310680

Abstract

For several decades now, it has been known that large quantities of hydrogen can be stored in the earth’s mantle. This hydrogen, which is disseminated as defect components in nominally anhydrous minerals (NAMs), can have an outsized influence on minerals’ bulk properties, potentially impacting planetary-scale processes. However, a description of how this hydrogen is sequestered in NAMs — its distribution between phases, its inhomogeneity between different mantle regimes, and the variety of defects involved — has evolved significantly with time. Deciphering hydrogen’s role in the deep earth requires a detailed understanding of how hydrogen incorporates into mantle phases, beginning at an atomistic and structural level. Unfortunately, for a variety of reasons, directly measuring the crystallographic positions of hydrogen in most NAMs represents an exceptionally high technical barrier. Thus, hydrogen’s structural state is, in many phases, incompletely understood. One approach for addressing this is to incorporate the use of computational methods like density functional theory (DFT) in the interpretation of analytical methods that can provide indirect structural information, like Fourier transform infrared spectroscopy (FTIR). This is the methodology employed by the work outlined in subsequent chapters.

This thesis focuses on two specific mineral structures found within the deep earth — the rutile and perovskite structures — and explores some of the many possible hydrogen defect states in these phases. These include not only the conventionally considered hydroxyl (OH⁻) group, but also hydride (H⁻), an anionic form of hydrogen whose role in the mantle has yet to be considered in detail. The predictive and interpretive capabilities of DFT are utilized in studies on stishovite, rutile-type TiO₂, SrTiO₃, and davemaoite to both elucidate hydrogen’s incorporated state in these phases and make predictions about yet-to-be-observed hydrogen defects. Detailed spectroscopic studies on rutile-type TiO₂ and SrTiO₃ perovskite provide new insights into both hydrogen and non-hydrogen related defect structures in these materials, with implications for future studies of NAMs.

Thesis Files