The Debye-Waller factor of stabilized delta-Pu

TL;DR

This study calculates the Debye-Waller factor for stabilized delta-phase plutonium with aluminum, revealing limitations of phonon softening models in explaining experimental thermal parameters across temperatures.

Contribution

It introduces a quasi-harmonic model to compute thermal atomic displacements in delta-Pu and discusses discrepancies with observed data.

Findings

Phonon softening alone cannot explain high-temperature thermal parameters.

The calculated Debye-Waller factor shows high values at low temperatures.

Implications for diffraction measurements on delta-Pu alloys are discussed.

Abstract

The Debye-Waller factor has been calculated for stabilized delta-phase plutonium with 5% aluminum. A quasi-harmonic Born-von Karman force model with temperature dependent phonon frequencies was used to calculate the mean-square thermal atomic displacement from absolute zero to 800 K. Implementation of the observed anomalous softening of the long wavelength phonons with increasing temperature cannot account for the softening of the measured thermal parameter at high temperatures nor for its rather high value at low temperatures. The implications for diffraction measurements on delta-phase stabilized plutonium alloys are discussed.