First-principles calculation of influence of nitrogen substituting for oxygen on the crystal structures and electronic band structures of Sr3MgSi2O8-σNσ

Abstract

In this work, influence of the nitrogen substituting for oxygen on the crystal structures and electronic band structures of Sr3MgSi2O8-σNσ (σ = 0, 0.125 and 0.250) materials had been investigated by the first-principles calculation. For the initial Sr3MgSi2O8 without nitrogen substitution, the band gap is about 5.889 eV between the conduction band and valence band. Analysis of its density of states (DOS) indicates that the conduction band is mainly constituted by Sr-d orbit. The valence band is mainly constituted by O-p orbit. After the nitrogen substituting for oxygen occurs, the band gap gradually decreases to 4.421 eV in the case σ = 0.250. Top of the valence band is still locating near 0 eV while bottom of the conduction band drops down to 4.421 eV. On the other hand, it can be observed that the N-p orbit hybridized into the top of the valence band which induced a new band above the O-p orbit. For Sr3MgSi2O8-σNσ materials with rare earth ions or transition metal ions serving as luminescence centres, this condition would influence the charge transfer process between the host materials and the luminescence centres. In addition, the energy needed for the substitution of one nitrogen anion for one oxygen anion is calculated to 89.50 eV. This illuminates clearly that the preparation condition of nitrogen oxide compounds is harsh. This work is helpful for better understanding the influence of nitrogen substituting for oxygen on the crystal structures and electronic band structures of Sr3MgSi2O8-σNσ materials.