Investigations of Technetium Metal and the Synthesis of Binary Technetium Nitrides under Extreme Conditions

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Technetium (Tc) is the lightest of the radioactive elements and has no stable isotopes. Significant quantities of Tc are not naturally occurring on earth. However, technetium is found in high fission yield in nuclear reactors and produced for medical imaging. With its long half life, and high mobility in the environment make it of particular interest. To that end, the fundamental chemistry of Tc and Tc compounds is not as well understood compared to neighboring elements on the periodic table. Therefore, fundamental studies designed to better understand this transition metal, coupled with more targeted investigation at high temperature and pressure should be undertaken.In the latter instance, the objective would be to create new materials with unique properties and potentially practical applications.The focus of this work is on technetium metal and the synthesis of binary Tc nitrides at extreme conditions. By utilizing the laser-heated diamond anvil cell (LHDAC) with the elemental combination of Tc and nitrogen I have synthesized two novel nitride compounds Tc2N and TcN, as well as a nonstoichiometric TcNx. In addition, the phase stability of Tc2N and TcN, from 0–50 GPa and up to 2500 K is reported. Determination of each phase and chemical stability of these Tc nitrides is important for potential applications such as targeted waste storage.My research has also discovered the property of magnetism in Tc, the second example in a 4d metal. I report a new allotrope of Tc, not previously reported or predicted. The phase transformation of Tc metal was observed at temperatures above 1500 K and pressures above 3.9 GPa in an LHDAC. The sample was recoverable at ambient conditions. With X-ray diffraction (XRD) and Raman scattering, I was able to identify the structure as tetragonal. Magnetic ordering was characterized based on the volume expansion and tetragonal distortion observed in the cell. New techniques for handling radioactive materials in the diamonds anvil cell are also discussed.

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