Emergent Properties in Intermetallic Bismuth Binaries
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badding-cathykb-phd-chemistry-2025-thesis .pdf
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15.53 MB
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54e9548d67ecf49ccc7429200d01a6c1
Author(s)
Badding, Catherine Kyoko
Advisor(s)
Freedman, Danna E.
Date Issued
May 2025
Publisher
Massachusetts Institute of Technology
Abstract
Tuning electronic and physical structures is crucial to developing technologies that utilize emergent properties. We chose to study transition metal and bismuth compounds because intuitively, bolstering the unpaired spins of transition metals with the spin-orbit coupling of a heavy element, such as bismuth, will result in a permanent magnet, like MnBi. However, many transition metal and bismuth compounds lack reactivity at ambient pressure using traditional solid-state synthetic techniques, necessitating alternative pathways for stabilizing these desired compounds. High-pressure experiments resulted in the first examples within the Fe–Bi, Co–Bi and Cu–Bi systems. CoBi₃, Cu₁₁Bi₇, and CuBi recover down to ambient pressure and physical properties measurements show they superconduct, highlighting how the identity of the transition metal can tune the emergent property observed. After the discovery of FeBi₂, subsequent theory predicts FeBi₂ to exhibit ferromagnetism and superconductivity based on the applied pressure, further demonstrating how tuning the electronic structure can tune the emergent property. However, FeBi₂ decomposes upon decompression, making characterization challenging. Following the principle that ferromagnetism needs localized unpaired spins and superconductivity needs paired spins, we aimed to replicate this tuned behavior via chemical modification and use transition metals with fewer unpaired spins, the same number of spins with more delocalized orbitals, and more paired spins compared to FeBi₂. We studied the Mn–Bi, Ru–Bi, and Co–Bi systems by synthesizing and characterizing metastable compounds at high pressure to understand the structure-property relationship further. We study the orbital contribution of Bi in the permanent magnetism of MnBi₂, the superconducting behavior of RuBi₄, and the possibility of coexistence of superconductivity and ferromagnetism in the Co–Bi system. These results show pathways for designing new materials with emergent properties based on tuning the d electrons of the transition metal and leveraging high-Z elements.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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