title: Novel chain structures in group VI elements.
abstract: Recent developments in high-pressure methods and advances in X-ray crystallography have led to a new level of understanding of phase diagrams and structures of materials under pressure. Recently discovered phenomena such as complex phases of alkali metals, incommensurate host-guest structures, and incommensurately modulated structures have rendered obsolete our conventional wisdom about the range of structures possible in the elements. Using new in situ diffraction techniques, we have resolved the long-standing problem of the phase-transition sequence of sulphur in its non-metallic state. We demonstrate that it is very different from that previously proposed, with only two phases stable between 1.5 GPa and 83 GPa (the pressure of metallization), and temperatures from 300 K to 1,100 K. The phases have a triangular chain and a squared chain structure. The same squared chain structure is found in the heavier group VI element selenium.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, District of Columbia 20015, USA. o.degtyareva@gl.ciw.edu <o.degtyareva@gl.ciw.edu>
authors.forename: Olga
authors.initials: O
authors.lastname: Degtyareva
authors.forename: Eugene
authors.initials: E
authors.lastname: Gregoryanz
authors.forename: Maddury
authors.initials: M
authors.lastname: Somayazulu
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Dera
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley