Synthesis and Magnetism at High Pressure

Klein, Ryan Alexander

doi:https://doi.org/10.21985/n2-e7cm-n492

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Synthesis and Magnetism at High Pressure

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In multiatomic systems, high applied pressures reduce interatomic contact distances. At pressures comparable to those inside planets, this relatively simple principle completely changes the guiding principles of chemistry and physics established at near-ambient conditions. High-pressure investigations of precisely how the laws of nature evolve in the gigapascal and megabar regime began over a century ago, with Percy Bridgman. Yet, high-pressure techniques only recently became easily available in chemistry laboratories with the development of the diamond anvil cell, and high-pressure chemistry is a young and developing field. As such, high-pressure research, especially with regards to synthesis and magnetism, represents a new scientific frontier. In this dissertation, I report two studies that investigate changes in chemical bonding as a function of pressure with implications for structure, conductivity, and magnetism. In Chapter 1, I broadly introduce outstanding problems in structure and magnetism at high-pressure. In Chapters 2 and 3 of this dissertation I report on the application of high pressure to generate a chemically-pure magnetostructural correlation study in the magnetically frustrated mineral jarosite. The comprehensive nature of the work allows elucidation of the underlying origins of the complex magnetism in jarosite. I show that the magnetism in jarosite is completely governed by two interactions up to 40 GPa: the Dzyaloshinskii-Moriya interaction and metal–ligand covalency in the crystallographic ab-plane. Above 40 GPa of applied pressure, there exists a continuous, nominally isomorphous structural phase transition coincident in pressure with a sudden collapse in magnetism. At the end of chapter 3, I provide several hypotheses that may explain the magnetic collapse. In Chapter 4, I report on the application of extreme pressure to morph the potential energy landscape in the Bi–V–O ternary system, which enabled the isolation of the novel, metastable BiVO3 perovskite. I show in this study that pressure effectively modifies the relative redox potentials in this system. This study serves as an example of the developing concept in high-pressure science that the electronegativities of the elements – and therefore the potential energy landscape along a complex reaction coordinate – change as a function of pressure.

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