Thermodynamic properties of rock-salt ZnO

• Assessment of thermodynamic data for ZnO in rock salt structure has been performed.
• Enthalpy of formation and entropy of ZnO in rock salt structure at 298 K have been evaluated.
• Temperature dependence of heat capacity of ZnO in rock salt structure has been assessed.
• High pressure stability of ZnO.

Zinc oxide represents an important material with a wide variety of applications. At the temperature T = 298.15 K and standard pressure p° = 100 kPa ZnO exists in the hexagonal wurtzite structure, which undergoes a transformation to rock salt polymorph under the pressure of ≈9 GPa. A consistent set of thermodynamic functions for ZnO in the high-pressure rock salt modification has been established on the basis of thorough evaluation of experimental and calculated data. Using literature data for wurtzite ZnO, standard enthalpy of formation at 298.15 K for rock salt ZnO have been assessed as ΔfH°(298.15 K) = −326.69 kJ mol−1. Standard entropy S°m(298.15 K) = 45.42 J K−1 mol−1 was derived from published low temperature heat capacity. The temperature dependence of the standard molar heat capacity above room temperature in the form C°pm = 45.91 + 0.009089T − 604976/T2 + 4.159 × 10−6T2 (J K−1 mol−1) has been derived. The dataset is consistent with the transition pressure ptr = 9.6 GPa for wurtzite to rock salt transformation at room temperature.