Extension of conventional solid state methods: Microwave synthesis of transition metal carbides

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In the proposed project, we will explore microwave heating as a synthesis tool to access a variety of binary and more complex transition metal carbides. Solid state microwave reactions have been widely used to prepare a multitude of inorganic compounds that often even exhibit improved properties. Based on our experience with microwave reactions using a domestic microwave oven (e.g. half-Heusler intermetallic compounds and oxide phosphors), we will extend our efforts to an additional class of compounds, namely transition metal carbides. Here, a laboratory-grade microwave reactor is the central piece of equipment that will be used during the course of this project. Although promising results can already be achieved with a domestic microwave oven, only the research-grade microwave will allow us to take full advantage of the microwave heating technique. It offers a number of advantages in contrast to the domestic microwave oven, most importantly the possibility to monitor the temperature during the reaction as well as much higher safety standards. Both aspects are of major importance for the here proposed project because they will enable highly reproducible syntheses as well as safe reaction procedures in the laboratory.Due to the excellent coupling behavior of different forms of carbon with the microwave radiation leading to rapid heating rates, carbides are among the ideal candidates to exploit microwave heating for their synthesis. Binary transition metal carbides, such as Fe3C, Co2C, will be studied to evaluate the various possible synthesis methods, direct reaction from the elements and carbothermal reduction of the respective oxides. We will then move towards the hexagonal MAX phases that are more complex carbides with the general formula Mn+1AXn, where M is an early transition metal, A is an A-group element (mostly in groups 13 and 14) and X is either carbon or nitrogen. Many of these compounds are known and well studied. However, not that much work has been devoted to finding additional MAX phases with later transition metals, such as Mn, Fe and Co. We will therefore focus on possible solid solutions of known MAX compounds with later transition metals and are particularly interested in their magnetic properties. Besides, so called MXene compounds will be also be investigated. They are an exfoliated version of the MAX phases where the A layer has been etched away. Since some of these compounds exhibit semiconducting instead of metallic behavior, they are expected to show promising thermoelectric properties.