HIGH-PRESSURE X-RAY-DIFFRACTION ON POTASSIUM AND RUBIDIUM UP TO 50-GPA

The effect of pressure on structural properties of potassium and rubid ium is studied with diamond-anvil cells by energy-dispersive x-ray dif fraction 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. Equa tion of state data for these heavy alkali metals are presented and com pared with earlier data for cesium.