Effect of transition/rare earth metal oxide additives on densification during sintering of Si₃ N₄

It is argued that the sintering and densification of Si₃N₄ based ceramics, using transition metal or rare earth metal oxide additives, can be described as an electronic mechanism involving a transfer of electrons into the Si₃N₄–SiO₂ valence band: this is consistent with a recently proposed model of bonding at metal/ceramic interfaces. Transition metal/rare earth metal oxides with a ‘metallic’ character tend to aid densification during sintering of Si₃N₄–β sialon whereas insulator type metal oxides are less effective densifiers. MST/1855.