High-pressure high-temperature synthesis and structure of β-MgSiN2

A new phase of magnesium silicon nitride, beta-MgSiN2, is synthesized in a laser-heated diamond anvil cell at pressure of 27 GPa and temperatures exceeding 2000 K. It crystallises in a rhombohedral caswellsilverite-type structure (space group R (3) over barm) with both Mg and Si atoms in octahedral coordinations - in agreement with earlier DFT calculations. In contrast to recent shock compression investigation, the beta-phase is found to metastably persist at ambient conditions. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim