Soft phonons in -phase plutonium near the transition

¹  Department of Physics, University of Illinois at Urbana-Champaign - 1110 W. Green Street, Urbana, IL 61801, USA
²  Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign - 104 S. Goodwin Avenue, Urbana, IL 61801, USA
³  Lawrence Livermore National Laboratory, University of California - P.O. Box 808, Livermore, CA 94551, USA
⁴  Advanced Photon Source, Argonne National Laboratory - Argonne, IL 60439, USA

Corresponding author: chiang@mrl.uiuc.edu

Received: 6 December 2007
Accepted: 18 February 2008

Abstract

Plutonium and its alloys exhibit complex phase diagrams that imply anomalous lattice dynamics near phase stability boundaries. Specifically, the TA [111] phonon branch in Ga-stabilized -Pu at room temperature shows a pronounced soft mode at the zone boundary, which suggests a possible connection to the martensitic transformation from the fcc -phase to the monoclinic -phase at low temperatures. This work is a study of the lattice dynamics of this system by X-ray thermal diffuse scattering. The results reveal little temperature dependence of the phonon frequencies, thus indicating that kinetic phonon softening is not responsible for this phase transition.