The standard molar enthalpies of formation of α−Si₃N₄ and β−Si₃N₄ by combustion calorimetry in fluorine, and the enthalpy of the α-to-β transition at the temperature 298.15 K

The standard molar enthalpies of formation Δ_fH°_m of α−Si₃N₄ and β−Si₃N₄ have been determined by fluorine combustion calorimetry: Δ_fH°_m (Si₃N₄, cr, α, 298.15 K) = − (828.9 ± 3.4) kJ · mol⁻¹ and Δ_fH°_m (Si₃N₄, cr, β, 298.15 K) = – (827.8 ± 2.5) kJ · mol⁻¹. These results indicate that the enthalpy of the α-to-β transition, approximately (1 ± 4) kJ · mol⁻¹, is negligible within experimental uncertainty.