High-Pressure Nitridosilicates, Oxonitridosilicates and Nitridophosphates and Related Binary Nitrides

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Within a broad and systematic approach, combining both synthetical and computational methods, we are targeting synthesis and structural investigation of novel and hitherto unknown high-pressure phases of ternary or higher nitridosilicates and oxonitridosilicates (sions). The preparative course of line will use our in-house Walker-type multianvil technique and laser-heated diamond anvil cells, while experiments will be paralleled by theoretical studies using density functional theory methods. The materials under investigation are structurally related to both classical (oxo)silicates and binary high-performance ceramics such as Si3N4 or AlN. In analogy with known high-pressure oxosilicates (e.g. stishovite), the new high-pressure compounds are expected to exhibit unprecedented crystal structures (condensed SiN6 octahedrons or even SiN5 units). This will result in outstanding micro- and macroscopic materials properties (e.g. hardness, bulk moduli, solid-state NMR chemical shifts, optical properties) which will be investigated. Computations will be carried out in advance to identify candidates for high-pressure transformations and to elucidate possible transition paths. Posterior, computations of properties (lattice parameter and vibrational spectra at high pressures, NMR chemical shifts) will corroborate results of experimental characterizations. A comprehensive understanding of structural stability and thermodynamic relation of the new phases within their respective phase diagrams will be achieved.