Band gap closure, incommensurability and molecular dissociation of dense chlorine

• Published in: Nature communications Vol. 10; no. 1; pp. 1134 - 7
• Main Authors: Dalladay-Simpson, Philip, Binns, Jack, Peña-Alvarez, Miriam, Donnelly, Mary-Ellen, Greenberg, Eran, Prakapenka, Vitali, Chen, Xiao-Jia, Gregoryanz, Eugene, Howie, Ross T.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08.03.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 140/133; 639/301/119/1002; 639/638/263; 639/766/119/2795; Amorphization; ATOMIC AND MOLECULAR PHYSICS; Bromine; Chlorine; Compressibility; Crystallization; Energy gap; High pressure; Humanities and Social Sciences; Iodine; Molecular structure; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-09108-x

Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra- and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the crystallization of chlorine at 1.15(30) GPa into an ordered orthorhombic structure ( oC 8), the existence of a mixed-molecular structure ( mC 8, 130(10)–241(10) GPa) and the concomitant observation of a continuous band gap closure, indicative of a transformation into a metallic molecular form around 200(10) GPa. The onset of dissociation of chlorine is identified by the observation of the incommensurate structure (i- oF 4) above 200(10) GPa, before finally adopting a monatomic form ( oI 2) above 256(10) GPa. Molecular systems are predicted to transform into atomic solids and be metallic at high pressure; this was observed for the diatomic elements iodine and bromine. Here the authors access the higher pressures needed to observe the dissociation in chlorine, through an incommensurate phase, and provide evidence for metallization.