Anionic superstructures in liquid Zintl phases

Abstract

In many liquid alloys of the alkali metals with members of the post-transition sp elements intermediate-range ordering occurs. It is supposed that in such alloys, which have an ionic character, the anions form clusters (polyanions). These clusters are remnants of the so-called Zintl ions, found in many of the corresponding solid alloys. Tetrahedral (Pb₄)⁴⁻ is an example. Liquid alloys belonging to the alkali–Ga, –Tl, –Sn, –Pb, –Sb, –Bi and –Te systems are discussed. Experimental evidence for the survival of Zintl ions is provided by measurements of the electronic, thermodynamic and structural properties. Special attention is paid to the analysis of neutron diffraction data. The impact of recently developed ab initio methods for simultaneous calculation of the atomic distribution and the electronic structure is demonstrated. Analogies with the solid counterparts play an important role. The conclusion is that there are many indications for the survival of Zintl ions in the liquid state but that they do not remain unimpaired on melting and heating.