Energetics of Ternary Nitrides: Li-Ca-Zn-N and Ca-Ta-N Systems

High-temperature oxide melt drop solution calorimetry was used to study the energetics of ternary nitride formation. The standard enthalpies of formation of several binary and ternary nitrides were determined. These values in kJ mol^-1 are ΔH_f^o(Li₃N) = -166.1 ± 4.8, ΔH_f^o(Ca₃N₂) = -439.7 ± 6.6, ΔH_f^o(Zn₃N₂) = -43.5 ± 4.1, ΔH_f^o(Ta₃N₅) = -849.7 ± 11.7, ΔH_f^o(Ca₂ZnN₂) = -378.9 ± 8.6, ΔH_f^o(Sr₂ZnN₂) = -385.6 ± 14.3, ΔH_f^o(LiCaN) = -216.8 ± 10.8, ΔH_f^o(LiZnN) = -137.5 ± 6.8, and ΔH_f^o(CaTaN₂) = -643.8 ± 9.6. These enthalpies of formation are small in magnitude compared to analogous values for oxides. However, the enthalpies of formation of the ternaries from binary nitrides can be quite substantial, confirming significant energetic stabilization of ternary nitrides. The energetics of ternary nitride formation appears to be dominated by the acid/base character of the cations. A linear relationship was found between the enthalpies of formation of the ternaries from binary nitrides and the ionic potential ratio of the two cations.