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Unusual phonon softening in delta-phase plutonium
R J McQueeney1, A C Lawson, A Migliori
1Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Phonon frequencies and sound velocities in plutonium-aluminum alloys significantly soften with rising temperatures. This unusual softening, especially in the transverse acoustic mode, may stem from temperature-dependent electronic structures in 5f-band metals.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Plutonium Alloys
Background:
- Understanding the behavior of plutonium alloys is crucial for nuclear materials science.
- Phonon properties and sound velocities are key indicators of material stability and response to temperature changes.
Purpose of the Study:
- To investigate the phonon density of states and adiabatic sound velocities in fcc-stabilized PuAl alloys.
- To characterize the temperature dependence of these properties and identify anomalous behavior.
Main Methods:
- Measurements of phonon density of states and adiabatic sound velocities.
- Analysis of temperature-dependent properties with varying alloy composition.
Main Results:
- Observed significant softening (decrease) in phonon frequencies and sound velocities with increasing temperature.
- Anomalously large softening (~30%) in the transverse acoustic branch along the [111] direction.
- High sensitivity of phonon softening to alloy composition.
Conclusions:
- The observed phonon softening is unusually large compared to other fcc metals.
- This phenomenon may be linked to the unique temperature dependence of the electronic structure in narrow 5f-band metals like PuAl alloys.
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