Keywords:First principle calculation, Density functional theory, Spinel
On basis of the first principle calculation, we report a possible nitrogen doped structure of MgAl2O4 spinel. The structural and electronic properties (include the band structure, density of states and phonon) of spinel (MgAl2O4) and N-doped spinel (MgAl2O3.5N0.5) compounds are performed using density functional theory (DFT). The density and space group of two crystal cells are 3.47 g/cm3 (Fd3m) for MgAl2O4 and 3.38 g/cm3 (R3m) for MgAl2O3.5N0.5, respectively. The calculated direct band gaps at the Γ-point are about 5.13 eV for MgAl2O4 and 4.24 eV for MgAl2O3.5N0.5, respectively. The projected density of states (PDOS) shows that the tops of the valence bands are built up from ~93% of p(O) states and ~60% of p(N) + ~32% of p(O) states (for MgAl2O4 and MgAl2O3.5N0.5, respectively). In the phonon analysis, the lowest frequency of MgAl2O3.5N0.5 is redshifted to 36.6 cm-1 (MgAl2O4 is 39.8 cm-1) caused by the N-doped. We also calculate their cohesive energy in the pressure range of 0-150 GPa. We found that the cohesive energy of MgAl2O3.5N0.5 is lower than MgAl2O4 at the pressure higher than ~115 GPa, it implies that MgAl2O3.5N0.5 is more stable than MgAl2O4 at high pressure. Finally, we suggest that nitrogen atom would replace the oxygen of spinel in the depths of the earth. The results imply the deep mantle may storage a considerable amount of nitrogen.