X-Ray Diffraction Study of Electronic Transitions in Cesium under High Pressure

Abstract

The crystal structure of the high-pressure phase of cesium (IV) was determined to be a tetragonal lattice with $Z=4$. The space group is ${{D}_{4h}}^{19}\ensuremath{-}\frac{I{4}_{1}}{\mathrm{amd}}$ and the lattice parameters are $a=3.349$ \AA{} and $c=12.487$ \AA{} at 8.0 GPa. From the structure it is deduced that the atomic radius of cesium decreases dramatically at the III-IV transition, which suggests a discontinuous $s\ensuremath{-}d$ electronic transition.