Electronic Structure and Bulk Properties of β‐SiAlONs

A series of β-SiAlONs with the composition Si6–zAlzOzN8–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.

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