Structure of Alkali Metals in the Liquid State

Neutron diffraction patterns have been obtained for the alkali metal liquids; lithium (180°C), sodium (100°C), potassium (65°C), rubidium (40°C, 160°C, 240°C, and 360°C), and cesium (30°C, 300°C, and 575°C). It was found necessary to correct intensities for scattering by a free atom for lithium and sodium but not for the heavier atoms. Atomic distribution curves were computed for all the above cases, and compared with results from x-ray diffraction. Just above melting temperatures the nearest-neighbor distances are for lithium 3.15 A, sodium 3.82 A, potassium 4.64 A, rubidium 4.97 A, and cesium 5.31 A, the number of nearest neighbors is, within one-half atom, about 9.0 to 9.5 atoms in each case. At elevated temperatures with rubidium and cesium, a weak subsidiary concentration of atoms appears between the usual first and second neighbor concentration.