An equation of state for alkali metals

Semi-empirical equations of state based on Lindemann's law have been developed to determine the pressure (P) dependence of the melting temperature (Tm) of Li, K, Rb and Cs. The basic inputs are Grüneisen parameter and the bulk modulus. Tm–P variations exhibit maximum melting temperature with concave downwards. The maximum in Tm for Cs is found to occur at pressure of 2.2GPa whereas for Li, K and Rb it falls in the range of 7–9.5GPa. The predicted values of Tm as a function of pressure, based on the present empirical relation, fit quite well with the available experimental data. The empirical relation can also be used to extrapolate Tm at higher pressure from the values available at lower pressures. •Developed equations for pressure dependence of melting temperature of solids.•Higher order terms are important to exhibit maximum and curvature of melting curve.•Maximum Tm of cesium occurs at much lower pressure.•Computed values are in very good agreement with available experimental results.