Static and shock-wave compression measurements as well as theoretical calculations show that I, Xe, Cs, Ba, and La exhibit similar behavior at high pressure determined by the transfer of electrons from $6s$- or $5p$-like states to nearby $5d$ conduction bands. In shock-wave experiments these transitions occur thermally, while in static experiments, they occur by transfer to degenerate states. Such transitions profoundly influence the high-pressure thermodynamic properties of these materials, as will be reviewed in this paper.

• Received 17 August 1981

DOI:https://doi.org/10.1103/PhysRevB.26.4088