title: Molecular-network-ionic structure transitions in liquid AlCl(3) and ZnCl(2) halogenides under pressure.
abstract: We present the in situ high-pressure-high-temperature x-ray diffraction study of the liquid AlCl(3) and ZnCl(2) halogenides having a quasi-molecular network structure in liquid state at normal pressure. These liquids are intermediate between pure covalent and ionic melts. Structural study of these liquid halogenides is indicative of a rapid and strong breakdown of an intermediate-range order in a tetrahedral network of melts for the initial pressure range, 0-2.5 GPa for AlCl(3) and 0-1.8 GPa for ZnCl(2), and points to rather sharp transitions in liquids with the formation of a short-range order structure similar to ionic melt structures around 4 GPa for AlCl(3) and 3 GPa for ZnCl(2). Thus, pseudo-covalent liquid halogenides like AlCl(3) and ZnCl(2) provide testimony to two phenomena under high pressures, namely, a gradual decay of structural correlations in the tetrahedral network of the melt and a sharp transition from molecular-network to ionic structure in liquid on further compression. 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.
authors.affiliation: Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia.
authors.forename: V V
authors.initials: VV
authors.lastname: Brazhkin
authors.forename: A G
authors.initials: AG
authors.lastname: Lyapin
authors.forename: S V
authors.initials: SV
authors.lastname: Popova
authors.forename: Y
authors.initials: Y
authors.lastname: Katayama
authors.forename: H
authors.initials: H
authors.lastname: Saitoh
authors.forename: W
authors.initials: W
authors.lastname: Utsumi