High pressure–high temperature investigation of the stability of nitride spinels in the systems Si3N4–Ge3N4

In this study, we used laser-heated diamond anvil cell techniques coupled with synchrotron X-ray diffraction to investigate the synthesis and stability of nitride spinels in the Si3N4–Ge3N4 system, at pressures close to 20 GPa and at temperatures up to >2000°C. The newly discovered nitride spinels were found to be stable over the entire pressure and temperature range studied. There is little incorporation of Si3N4 component in γ-Ge3N4, but we observed formation of a new ternary nitride spinel (SixGe1−x)3N4, with x∼0.6. The analysis of the X-ray patterns indicates that Si4+, normally considered to be the smaller ion, is strongly partitioned into the octahedral sites in the spinel phase. Excess Ge4+ ions may also occupy these octahedral sites in the experimental synthesis at high pressure and temperature.