Electronic Structure and Bulk Properties of β‐SiAlONs

A series of β‐SiAlONs with the composition Si _{6– z} Al _z O _z N _{8– z} ( z = 0.5–4) is prepared by hot isostatic pressing. Evaluated bulk moduli are compared with those calculated using the first‐principles method. Theoretical values are derived from the fit of the energy versus volume dependence. In total‐energy calculations full relaxation of all atomic positions within a supercell is performed. Both experimental and theoretical bulk moduli compare reasonably well and show the decrease in value from ∼240 GPa ( z = 0) to ∼170 GPa ( z = 4). For the O/N substitutions no preferential occupation of the lattice N sites is observed. Both Al/Si and O/N substitutions cause the local expansion of the structure. In the relaxed structures a sphere of decreased interatomic distances surrounds each substitution site, thus compensating for effect of the local expansion. The increasing Al–O/Si–N substitution rate causes a smooth change of the shape and position of the energy bands. The band gap between occupied and unoccupied states is getting narrower, thus decreasing the isolating properties of the material.