Experimental equations of state for cesium and lithium metals to 20 kbar and the high-pressure behavior of the alkali metals

Abstract

Experimental equation-of-state results to 20 kbar and from 4 K to room temperature are given for cesium and lithium metals which are comparable with those published previously for sodium, potassium, and rubidium [Phys. Rev. B 28, 5395 (1983)]. The same generalization holds that the isothermal bulk modulus is a function of the volume only. Cesium and lithium each are slightly more compressible in a reduced sense than the other three alkali metals, and have Grüneisen parameters (1.14 and 0.878, respectively) which are smaller than the common value for the others, 1.25. Extrapolations of the present results for the alkali metals are compared with other data to 100 kbar, with these earlier results scattering about the extrapolation. It is suggested that the bcc-to-fcc transitions in potassium, rubidium, and cesium occur at common values of the ratio of the nearest-neighbor distance to the ionic or pseudopotential radius. No systematic trends are observed in these equation-of-state results which can be associated with an increase in s-d mixing effects with increasing ionic mass.