Functional transition metal nitrides

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Transition metal nitrides play a central role in modern solid-state chemistry and materials science owed to abundant important properties and applications such as hard ceramic abrasives, catalysts, magnetism of itinerant and localized electrons, remarkable dielectricity and proposed ferroelectricity, as well as useful transport properties of semiconductors, superconductors, and Li-ion conductors. However, the discovery of new materials is currently stagnating owed to the difficult thermodynamics of nitride chemistry. In preliminary work, we presented a solution to the preparative difficulties through high-pressure synthesis of novel nitrides such as perovskite LaReN3 and highly oxidized nitridoferrate Ca4FeN4. In this Emmy-Noether programme, Functional Transition Metal Nitrides, we systematically explore nitridometallates and nitride perovskites with ambient and high-pressure synthesis methods. We employ large-volume-presses for direct synthesis of nitrogen-rich materials such as nitride perovskites, Ruddelsden-Popper phases, and highly oxidized nitridometallates. We continue exploration of nitrogen-poor systems with ambient pressure methods, and emphasize will be put on defect perovskite and Ruddelsden-Popper types. These defect phases will be further topotactically nitrided in diamond anvil cells under extreme nitrogen pressures. As the electronic properties of transition metal nitrides are governed by the covalency of the metal-nitrogen bonds, we expect a unique materials chemistry much different from oxides. Perovskite nitrides offer a large flexibility in compositions so that properties such as transport and magnetism stemming from electron correlation can be tuned and explored. Especially, the interplay of spin-orbit coupling, electron-phonon coupling, and lattice degrees of freedom and their effect on structure and properties will be studied. Chemical substitutions will be used to tune valence electron configuration to investigate the physics of nitrides at the metal-insulator transition. In nitridometallate chemistry, we pursue the stabilization of high oxidation states in nitrides and investigate their structural chemistry and properties. Open-shell systems are expected to show interesting itinerant or localized electron magnetic behaviour, while closed-shell systems are usually semiconductors, which may be useful for energy conversion applications. This Emmy-Noether project combines challenging inorganic synthesis with advanced analysis methods from solid-state physics to create a new interdisciplinary field of nitride research. The targeted materials present a unique opportunity to improve the fundamental understanding of nitrides and the results will be of interest to all fields of inorganic chemistry, materials science, and solid-state physics.