Evidence for a paracrystalline bcc lattice in molten alkali metals

It is proved that the structure of molten Li, Na, and K is given by a convolution polynomial with bcc microparacrystalline domains with a mean interatomic distance $r_0$ larger than in the solid state at the melting point and paracrystalline distance fluctuations $g_{\mathrm{ik}}$ of (12-16)%. An fcc lattice can be excluded. Within the errors of experiments body-centered-tetragonal lattices are also possible, but the ratio $\frac{c}{a}$ must lie between 0.9 and 1.1. From the density and $r_0$ values it can be concluded that about (2-5)% of the atoms lie on interstitial places or belong to fcc microdomains. This effect is attributed to the lower packing density of the bcc lattice, since in fcc melts (for example, lead) $r_0$ does not change at the melting point and instead of interstitials atomic vacancies appear.