Thermodynamic, thermochemical and thermophysical properties of HgBr2.

Abstract

For mercury dibromide HgBr2, a promising component of the work-ing mixture of gas-discharge exciplex sources of coherent (lasers) and spontaneous (exciplex lamps) radiation, as well as a promising nonlin-ear 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 ther-mochemical (enthalpy ΔHf and Gibbs energy ΔGf of formation) func-tions 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 thermophysi-cal properties of HgBr2: isochoric heat capacity CV, Debye tempera-ture θD, volume thermal expansion αV, isothermal compressibility βT(isothermal bulk modulus BT= 1/βT), Grüneisen constant γG, phonon longitudinal vl, transverse vs, average –vvelocities and phonon thermal conductivity κ. In the present work, it was found that crystalline mer-cury dibromide expands strongly upon heating and has a low phonon thermal conductivity.