Energetics of cubic Si₃N₄

High-temperature oxide melt drop solution calorimetry was used to study the energetics of formation of cubic silicon nitride prepared at high pressure. The standard enthalpy of formation of c-Si₃N₄is −776.3 ± 9.5 kJ/mol. The calorimetric measurement of Si₃N₄in 3Na₂O·4MoO₃solvent was validated by comparing the enthalpy of formation for β–Si₃N₄with previous work using alkali borate solvent. The enthalpy of transformation from β– to c-Si₃N₄is 80.2 ± 9.6 kJ/mol. This value appears consistent with the observed synthesis conditions, which do not represent reversed equilibrium reactions.