Effect of interstitial lithium atom on crystal and electronic structure of silicon oxynitride

Plane-wave pseudopotential total energy method was used to calculate the effects of impurity Li atom on crystal structure, electronic and dielectric properties of Si 2 N 2 O. It is proved that Li atom prefers to occupy interstitial site than to substitute the Si atomic site. In addition, the presence of interstitial Li atom leads to relaxation of internal coordinates of Si, N, and O atoms, and bring out a different X-ray diffraction (XRD) pattern compared with that of a pure Si 2 N 2 O. The result is helpful to understand the diversity of experimental XRD data for Si 2 N 2 O sintered with and without Li 2 O additive. The theoretical polycrystalline dielectric constant of Li-doped Si 2 N 2 O is larger than that of a pure one, which can be attributed to a reduction of band gap. The mechanism is that interstitial Li atom provides extra electronic states at the bottom of conductive band.