Melting temperature, adiabats, and Grüneisen parameter of lithium, sodium and potassium versus pressure

Abstract

The pressure dependence of the melting temperatures of Li, Na, and K were measured to 32 kbar with accuracies in pressure and temperature of ±0.4% and ±0.25°C, respectively. The measurements were made in a piston cylinder apparatus with a fluid-pressure medium. The adiabatic pressure derivatives of temperature ${\left(\frac{\partial T}{\partial P}\right)}_s$ were measured to 32 kbar and 400°C by a pressure pulse method. The logarithm of ${\left(\frac{\partial T}{\partial P}\right)}_s$ decreases linearly with volume. The changes of ${\left(\frac{\partial T}{\partial P}\right)}_s$ at the liquid-solid transitions fall within the data scatter. The Grüneisen parameter was calculated from $\gamma =\left(\frac{B_s}{T}\right){\left(\frac{\partial T}{\partial P}\right)}_s$, where $B_s$ is the adiabatic bulk modulus. For all three alkali metals, $\gamma$ decreases with compression in both the solid and the liquid states, and at constant volume $\gamma$ decreases with temperature.