Structural phase transition in deuterated benzil C14 D10 O2: Neutron inelastic scattering

D. J. Goossens, T. R. Welberry, M. E. Hagen, J. A. Fernandez-Baca

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Abstract

Neutron inelastic scattering has been used to examine the structural phase transition in deuterated benzil C14 D10 O2. The transition in benzil, in which the unit cell goes from a trigonal P 31 21 unit cell above TC to a cell doubled P 21 unit cell below TC, leads to the emergence of a Bragg peak at the M -point of the high temperature Brillouin zone. It has previously been suggested that the softening of a transverse optic phonon at the Γ -point leads to the triggering of an instability at the M -point causing the transition to occur. This suggestion has been investigated by measuring the phonon spectrum at the M -point for a range of temperatures above TC and the phonon dispersion relation along the Γ-M direction just above TC. It is found that the transverse acoustic phonon at the M -point is of lower energy than the Γ -point optic mode and has a softening with temperature as T approaches TC from above that is much faster than that of the Γ -point optic mode. This behavior is inconsistent with the view that the Γ -point mode is responsible for triggering the phase transition. Rather the structural phase transition in benzil appears to be driven by a conventional soft TA mode at the M -point.

Original languageEnglish
Article number134116
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume73
Issue number13
DOIs
StatePublished - 2006

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