Volume 82, Number 2, April 2008
Article Number 26001
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 26 March 2008
EPL, 82 (2008) 26001
DOI: 10.1209/0295-5075/82/26001

Soft phonons in $\mth{\delta}$-phase plutonium near the $\delta-\alpha'$ transition

Ruqing Xu1, 2, Joe Wong3, Paul Zschack4, Hawoong Hong2 and Tai-C. Chiang1, 2

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

received 6 December 2007; accepted in final form 18 February 2008; published April 2008
published online 26 March 2008

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 $\delta $-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 $\delta $-phase to the monoclinic $\alpha'$-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.

63.20.D- - Phonon states and bands, normal modes, and phonon dispersion.
64.70.K- - Solid-solid transitions. - X-ray scattering (including small-angle scattering).

© EPLA 2008