Phase stability of highly compressed cesium

The crystal structure of cesium at pressures above similar to 70 GPa has be en investigated using angle-dispersive powder x-ray-diffraction techniques. The modification Cs-VI is found to be double hexagonal close packed (dhcp) , which is one of the two possible arrangements proposed earlier. No other phase transition is observed at pressures up to 184(20) GPa. We also presen t ab initio calculations of the pressure-dependent enthalpies of the phases Cs-IV (tetragonal), Cs-V (orthorhombic), and Cs-VI relative to that of a h cp lattice. In these calculations all structural parameters were optimized. The theoretical results are in full agreement with the experimentally obse rved phase transition sequence and structural parameters.