High-Pressure Synthesis, Electron Energy-Loss Spectroscopy Investigations, and Single Crystal Structure Determination of a Spinel-Type Gallium Oxonitride Ga_2.79◻_0.21(O_3.05N_0.76◻_0.19)

Under high-pressure/high-temperature conditions of 5 GPa and 1250 °C, the cubic phase Ga 2.79 ◻ 0.21 (O 3.05 N 0.76 ◻ 0.19 ) (◻ = vacancy) was synthesized in a Walker-type multianvil apparatus. For the first time, the crystal structure of a gallium oxonitride was determined on the basis of single crystal X-ray diffraction data. The cubic spinel-type gallium oxonitride crystallizes in the space group Fd 3̅ m (No. 227) with a lattice parameter a 0 = 827.8(2) pm. The combination of energy-dispersive X-ray spectroscopy (EDS) with electron energy-loss spectroscopy (EELS) allowed the quantification of nitrogen and oxygen for structural refinement. In the literature dealing with oxonitrides, crystal defects in spinel-type materials are handled with different models, mainly the approximation of a constant anion model. The present results indicate that this model is questionable, and one should also take into account a model with both cation and anion vacancies. Furthermore, a linear relationship between the lattice parameters and the ratio N/O in the gallium oxonitrides is questionable.