Thermodynamic properties of the alkali metals at high pressures and high temperatures

The melting temperatures of Li, Na, K, Rb, and Cs versus pressure were measured to 32 kbar in a piston cylinder apparatus with hydrostatic pressure medium and in situ pressure measurements. The accuracies in pressure and temperature are +/- 0.4% and +/- 0.250C, respectively. Substantial deviation from measurements using solid, non-hydrostatic pressure media is observed. The adiabat, (deltaT/deltaP)/sub s/, was measured to 32 kbar and 4000C by adiabatic compression. Ln (deltaT/deltaP)/sub s/ is a linear function of volume with good consistency in the slopes. (deltaT/deltaP)/sub s/ changes insignificantly at the liquid-solid phase transitions. The Grueneisen parameters, calculated from γ = B/sub s//T (deltaT/deltaP)/sub s/, decreases with pressure and temperature. B/sub s/ is the adiabatic bulk modulus. The γ-volume curves show strong curvature and γ tends to become volume independent at compressions of about 30%. γ increases by several percent at the liquid-solid transition