title: Vibrational dynamics and stability of the high-pressure chain and ring phases in S and Se.
abstract: The high-pressure phases of group-VI elements sulfur and selenium in their spiral chain and ring structures are examined by in situ Raman and x-ray diffraction techniques combined with first principles electronic structure calculations. The S-II, S-III, Se-I, and Se-VII having spiral chain structures and S-VI with a molecular six-member ring structure are studied in a wide P-T range. The square spiral chain structure of S-III and Se-VII is characterized by seven Raman modes that harden with increasing pressure. The calculations reproduce the observed frequencies and allow the authors to make the mode assignment. The "p-S" and "hplt" phases of sulfur reported by previous Raman studies are identified as S-II and S-III with the triangular and square spiral chain structures, respectively. The phase relations obtained by the x-ray and Raman measurements show that the high-pressure high-temperature phases of sulfur, observed by x-ray, can be induced by laser illumination at room temperature.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Degtyareva
authors.forename: Eduardo R
authors.initials: ER
authors.lastname: Hernández
authors.forename: Jorge
authors.initials: J
authors.lastname: Serrano
authors.forename: Maddury
authors.initials: M
authors.lastname: Somayazulu
authors.forename: Ho-kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Eugene
authors.initials: E
authors.lastname: Gregoryanz
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley