The System Si-Al-O-N at Extreme Pressures: A Synthetic and Computational Route to Novel Materials?

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Our main goal will be to locate potential new high density phases within the system Si¿Al¿O¿N in particular in the subsystems Si2N2O. . .Al2O3 and Si3N4. . .AlN. In order to provide a firm basis we will synthesise large single crystals of ¿-Si3N4 and rocksalt type AlN (rs-AlN) based on our own preliminary work using multi-anvil techniques. Large crystals will enable us to characterise physical properties (elastic properties, electronic structure, vibrational spectra) very accurately, providing a stringent test for theoretical results. Existence of ternary (Si¿O¿N) and quarternary (Si¿Al¿O¿N) phases will then be probed using static high pressure techniques supplemented by shock wave synthesis in order to produce larger amounts of material. The products will be subjected to thorough characterisation including X-ray, IR-microscopy and micro-Raman spectroscopy, analytical high resolution TEM, EPMA, SIMS/SNMS and solid state NMR. Theoretical investigations on these systems will be based on first-principles density-functional theory calculations. The project will provide fundamental insight into the largely unknown phase behaviour of the system Si¿Al¿O¿N at high pressures and high temperatures.