[P-CG22] Shock responses of planetary materials elucidated from meteorites and dynamic compression experiments

[PCG22-P08] First-principle study of the structural and electronic properties of N-doped MgAl₂O₄ spinel

*Chi Pui Tang¹, Pak Kin Leong¹, Toshimori Sekine^2,3 (1.State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, 2.Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai Laboratory of HPSTAR, Shanghai, P.R. China, 3.Graduate School of Engineering, Osaka University)

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 (MgAl₂O_3.5N_0.5) 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 MgAl₂O_3.5N_0.5, respectively. The calculated direct band gaps at the Γ-point are about 5.13 eV for MgAl₂O₄ and 4.24 eV for MgAl₂O_3.5N_0.5, 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 MgAl₂O_3.5N_0.5, respectively). In the phonon analysis, the lowest frequency of MgAl₂O_3.5N_0.5 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 MgAl₂O_3.5N_0.5 is lower than MgAl₂O₄ at the pressure higher than ~115 GPa, it implies that MgAl₂O_3.5N_0.5 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.