Thermodynamic, thermochemical and thermophysical properties of HgBr2

For mercury dibromide HgBr2, a promising component of the working mixture of gas-discharge exciplex sources of coherent (lasers) and spontaneous (exciplex lamps) radiation, as well as a promising nonlinear optical crystal for the infrared radiation process, thermodynamic and thermochemical properties in the temperature range 173–512 K were investigated. The established basic thermodynamic (isobaric heat capacity Ср, total entropy S, enthalpy H and Gibbs energy G) and thermochemical (enthalpy ΔHf and Gibbs energy ΔGf of formation) functions of HgBr2 were compared with the known literature data at 298–514 K. The obtained results differed from the literature within 1–2% (for Ср), 0.1–0.2% (for S, H and G) and 0.1–0.6% (for ΔHf and ΔGf). The experimental data, combined with semi-empirical approaches and ab initio calculations taken from the literature, were used to estimate the previously unknown additional thermodynamic and thermophysical properties of HgBr2: isochoric heat capacity CV, Debye temperature θD, volume thermal expansion αV, isothermal compressibility βT (isothermal bulk modulus BT = 1/βT), Grüneisen constant γG, phonon longitudinal vl, transverse vs, average –v velocities and phonon thermal conductivity κ. In the present work, it was found that crystalline mercury dibromide expands strongly upon heating and has a low phonon thermal conductivity.