The discovery of dense spinel nitride phases,
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-Si
3N
4 and
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-Ge
3N
4, synthesized under high-pressure-high-temperature conditions has resulted in renewed interest in solid-state nitridematerials chemistry. The new materials are high hardness ceramics, and they represent anew family of wide band gap semiconductors and optoelectronic materials. The compoundshave been characterized by X-ray and electron diffraction and by Raman scattering carriedout both on quenched samples and in situ at high pressure in the diamond anvil cell. Here,we assign the Raman-active modes of
![](/images/gifchars/gamma.gif)
-Si
3N
4 and
![](/images/gifchars/gamma.gif)
-Ge
3N
4 spinels, taking account of impurityphases that can be present within the samples. Laser-heating diamond anvil cell studiescarried out at high pressures and at various temperatures lead to the identification ofadditional Raman features that we assign to the presence of defects, most likely N
3-vacancies, within the nitride spinels. The intensity of the "defect" peaks varies systematicallywith the temperature and pressure of synthesis, corresponding to changes in the N
2 activityin equilibrium between the solid nitrides and the surrounding N
2 fluid. The results pointthe way toward future measurement and control of the defect chemistry achieved withinspinel nitrides prepared under high-pressure-high-temperature conditions.