ELECTRONIC-STRUCTURE BEHIND THE MECHANICAL-PROPERTIES OF BETA-SIALONS

High-purity beta-sialons (Si6-zAlzOzN8-z) have been fabricated by hot-isostatic-pressing and their mechanical properties were examined. Young's modulus and Vickers hardness decreased almost linearly with the increase of z-value. The decrease was ascribed to the lattice softening, which was confirmed by Raman spectroscopy. At high temperatures, creep rate of sintered materials and also sintering rate of powders were significantly enhanced with the increase of z-value. Molecular orbital calculations for model clusters were performed by means of discrete-variational (DV) X(alpha) method. The electronic structures were quantitatively evaluated by Mulliken population analysis. Strength of covalent bonding expressed as overlap population was found considerably decreased at around the solute atoms, especially at Al atoms, which has been proposed as the electronic mechanism behind the above properties of beta-sialons.