Phase stability of highly compressed cesium

The crystal structure of cesium at pressures above similar to 70 GPa has been 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 present 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 hcp lattice. In these calculations all structural parameters were optimized. The theoretical results are in full agreement with the experimentally observed phase transition sequence and structural parameters.