Site preferences in β-sialon from first-principles calculations

Abstract

First-principles calculations based on density-functional theory (DFT) within the pseudo-potential method have been performed to identify site preferences in β-sialon, Si_6−zAl_zO_zN_8-z. With increasing z the calculated lattice volume increases while the bulk modulus decreases; calculated values are in excellent agreement with the experimental data. The calculations also showed that the atomic arrangements with the maximum number of Al–O and Si–N bonds have the lowest energy. There are different Si(O,N)₄ and Al(O,N)₄ tetrahedra in the sialons, which is in line with the results of NMR experiments. Meanwhile, the calculated occupations of oxygen at 2c sites are still different from those determined by neutron diffraction, which indicates the necessity of microdomain models for these compounds.