Shedding light on solid-state microwave synthesis:In-situ Raman spectroscopy during formation of layered NaxCoO2

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The goal of the proposed work is to gain insights about the influence of microwave radiation on the formation mechanism as well as composition and morphology of the products during high-temperature synthesis of layered inorganic materials. Microwave heating of solids and mixtures thereof is a powerful synthesis technique to access a large variety of inorganic compounds. However, the involved mechanisms are still not well understood. In order to fill this void, we will develop a unique and powerful Raman spectroscopy system coupled to a microwave oven that will allow us to collect in-situ data during microwave heating. The layered oxide family NaxCoO2 (x = 1, 0.74, 0.6, 0.5) will serve as the model system for all planned experiments since the synthesis can be performed in air (no inert gas needed) and the precursors and different structures (depending on x) exhibit distinct Raman signals. Two different synthesis methods, solid-state synthesis starting from solid powder mixtures as well as sol-gel synthesis starting from soluble metal salts, will be investigated. This will enable gaining insights into the role of the nature of the precursors and the different types of chemical reactions that lead to the final products. Ultimately, the comparison of the obtained Raman spectroscopy data during microwave-assisted and conventional heating will shed light on the influence of the microwave radiation on high-temperature synthesis (solid-state and sol-gel). Once the in-situ measurement system has been proven successful for the oxide model system, the in-situ analysis will be extended to the more challenging synthesis of layered ternary metal carbides (MAX phases). The knowledge about the formation mechanisms and the influence of microwave radiation on the synthesis and morphology of these phases will provide guiding principles for the control of the synthesis of layered inorganic materials (e.g. oxides and carbides) and open a path to new members/morphologies of these classes of materials.