High-pressure phases of the alkali metals

A series of recent x-ray diffraction experiments carried out by scientists from the Max-PlanckInstitut FKF in Stuttgart and the ESRF in Grenoble on elemental semiconductors and alkali metals under high pressure have provided new insight in pressure induced structural transformations. New structures have been identified, and some of these have surprising similarities, such as low coordination numbers. The new lithium phase, Li-cI16, which has a cubic structure with 16 atoms in the cubic cell, has not been found for any other element. Theoretical studies, some of which are described here, using ab initio methods to calculate electronic and structural properties provide theoretical support for the analysis of these experiments, and may also serve to predict new properties, such as superconductivity, of the materials when exposed to very high pressures.