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 degreesC. 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 gamma -Ge3N4, but we observed formation of a new ternary nitride spinel (SixGe1-x)(3)N-4, with x similar to 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. (C) 2001 Elsevier Science Ltd. All rights reserved.