Thermodynamic Properties of Solid Neon from a Helmholtz- Energy Equation of State up to 328 K and 200 GPa

Thermodynamic property data for solid neon have been analysed to construct a new fundamental equation of state (EOS) expressed in terms of the Helmholtz energy. The formulation follows the quasi-harmonic Debye–Grüneisen framework and adopts the same Helmholtz-energy structure as that used for solid argon, consistent with the general strategy previously developed for solid CO₂, benzene, and argon [J. Phys. Chem. Ref. Data 40, 043105 (2011); 50, 043104 (2021); Int. J. Thermophys. 46, 14 (2025)]. This EOS is thermodynamically coupled to a reference fluid EOS developed by Thol et al. [2] along sublimation/melting curves, enabling a consistent description of the solid-fluid phase equilibrium well as the compressed single-phase solid up to 328 K and 200GPa. The model is regressed to a comprehensive literature dataset covering cell volume, isobaric heat capacity, thermal expansivity, isothermal and isentropic bulk modulus, phase-equilibrium pressure and phase-transition enthalpy. Within its intended range of application, the EOS reproduces the fitted molar volumes typically within about 0.1% along the sublimation curve, and 0.5% along both the melting curve and in the compressed solid, while the heat capacity and thermal expansivity are represented with uncertainties of order 3–10% depending on the temperature. Isothermal and isentropic bulk modulus are described to within about 3% and 4%, respectively, and sublimation and melting pressures are represented within approximately 2% and 5%. Overall, the new Helmholtz-energy EOS provides a compact and physically consistent description of the thermodynamic properties of solid neon suitable for use in cryogenic and high-pressure applications.