Molecular-network-ionic structure transitions in liquid AlCl and ZnCl halogenides under pressure

Brazhkin, V. V.*; Lyapin, A. G.*; Popova, S. V.*; Katayama, Yoshinori; Saito, Hiroyuki; Utsumi, Wataru

Liquid AlCl and ZnCl halogenides are studied by high-pressure high-temperature X-ray diffraction measurements. These halogenides have a quasi-molecular network structure in liquid state at normal pressure. They are intermediate between pure covalent and ionic melts. The present study is indicative of a rapid and strong breakdown of an intermediate range order in a tetrahedral network of melts for the initial pressure range and points to rather sharp transitions in liquids with the formation of a short-range order structure similar to ionic melt structures. Such a two-stage structural transformation under pressure is the general feature for a wide class of simple melts, including most of the pseudo-covalent halogenides.