The reactivity and polymorphism of selected nitrides at high temperatures and high pressures

The reactivity and polymorphism of the nitrides of calcium, magnesium, silicon and germanium have been studied in Tuttle cold-seal, Bridgman-anvil, and internally-heated high-pressure high-temperature, equipment. A new orthorhombic phase of Ca₃N₂ has been formed at 46kb and 1800°C. The α → β transformation of Si₃N₄ has been studied at 47kb and 2000°C, under which conditions the β form was shown to be stable. Ternary nitrides could not be formed from binary mixtures of the basic and acidic nitride under conditions of high pressure and temperature probably because of kinetic barriers (with Si₃N₄) or dissociation (with Mg₃N₂ and Ge₃N₄).