Within this thesis we investigate the physical properties of iron-carbon-nitrogen alloys with implications for planetary cores. We employ high pressure mineral physics techniques to determine the Raman Scattering of Rhenium for Secondary Pressure Calibration, investigate the Strength, plasticity, and spin transition of Fe-N compounds in planetary cores, investigate the liquid Structure of iron-nitrogen-carbon alloys within the cores of small terrestrial bodies, and measure the Physical Properties of Transition-Metal Enriched Davemaoite in the Earth's lower mantle. Terrestrial planetary cores consist of Fe-Ni alloys enriched in light elements. Nitrogen and carbon are considered potential core constituents due to their highly siderophile nature and their high Poisson’s ratio when alloyed with iron. These light-element-bearing alloys can be studied experimentally using various high-pressure devices, including the Paris-Edinburgh press and the diamond anvil cell. Accurate pressure calibration is critical for successful high-pressure experiments. Previous studies have shown that different calibrations of the same material can deviate by more than 10% in the multi-megabar regime—a significant uncertainty given that Earth’s core spans 1.3 to 3.6 Mbar. In chapter two, we review various pressure calibrations and develop a secondary pressure scale based on the Raman scattering of Re, a common gasket material in diamond anvil cell experiments. This equation of state can be used to validate pressure conditions, monitor pressure gradients across the sample chamber, and predict diamond failure. In chapters three and four, we investigate the physical properties of Fe-light element alloys. In chapter three, we examine the strength, plasticity, and a transition in the electronic spin (i.e spin transition) of solid Fe-N compounds up to 60 GPa and 300 K using the diamond anvil cell. We find that nonhydrostatic stress broadens pressure range of the spin transition, Fe-N alloys develop unique textures and lattice preferred orientation, and nitrogen strengthens Fe at high pressures. These findings, combined with elasticity measurements, can be used to model the seismic properties of planetary cores in bodies such as Mars, Mercury, and the Moon. In chapter four, we explore the liquid structure of molten iron-nitrogen-carbon alloys under high pressure using the Paris-Edinburgh press, reaching up to 7 GPa and 1900 °C. We observe that increasing nitrogen and carbon content expands the liquid volume by increasing Fe-Fe bond distances, which we model using a modified Birch-Murnaghan equation of state. From these results, we infer that nitrogen and carbon incorporation in liquid iron could contribute to the density deficit observed in the cores of terrestrial bodies. In chapter five, we shift focus to investigating the thermal equation of state of Mn- and Fe-bearing davemaoite. Davemaoite is one of the primary minerals in the lower mantle and was recently found to form a partial solid solution with MnSiO3. We measure the thermal properties of davemaoite under lower mantle conditions and determine that Mn and Fe systematically influence its thermal behavior. Specifically, Fe and Mn shift the tetragonal-to-cubic phase transition to higher temperatures. However, given the realistic abundances of Fe and Mn dissolved in davemaoite, their presence would not make it seismically distinguishable from pure CaSiO3 in the lower mantle.
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