High-pressure x-ray diffraction on potassium and rubidium up to 50 GPa

The effect of pressure on structural properties of potassium and rubidium is studied with diamond-anvil cells by energy-dispersive x-ray diffraction with synchrotron radiation at room temperature up to 50 GPa. The K III structure of potassium at pressures above 23 GPa is indexed by the use of a tetragonal-body-centered lattice (tI16) with 16 atoms in the unit cell. A new phase is found for rubidium above 46 GPa. Equation of state data for these heavy alkali metals are presented and compared with earlier data for cesium.