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Session Q13 - DCMP: Elemental and Compound Glasses
Invited session, Friday morning, March 24, 8:00
Room B4, San Jose Convention Center
Network glasses featuring Se bonded to group IV and/or group V atoms are interesting because of the variety of electronic, optical and transport phenomena related to light-induced structural changes which they display. In addition, they have provided a rich proving ground for theories and experiments of chemical bonds acting as mechanical constraints affecting vibrational dynamics. The assignments of vibrational modes observed by a variety of spectroscopies and their connection to structural issues such as the presence of intermediate range order have also been areas of intense research and some controversy. Neutron scattering measurements have played a significant role over the last fifteen years in elucidating structure and dynamics in these glasses. Recent neutron time-of-flight measurements Kamitakahara, Didarul Islam and L.E. McNeil made at the Fermi-Chopper spectrometer at NIST on GeSe _2 and on related Ge-Sn-Se glasses coupled with ab initio molecular dynamics studies Drabold and Mark Cobb will be discussed which suggest a new interpretation of the A_1 companion mode found in these materials: a motion having substantial bond-stretching character localized on tetrahedra having one singly-bonded Se atom.