Vibrational properties of Ga-stabilizedδ−Puby extended x-ray absorption fine structure

Abstract

Temperature-dependent extended x-ray absorption fine structure (EXAFS) spectra were measured for a 3.3 at.% Ga stabilized Pu alloy over the range $T=20--300 \mathrm{K}.$ EXAFS data were acquired at both the Ga $K\mathrm{edge}$ and the Pu ${L}_{\mathrm{III}}$ edge. Curve fits were performed to the first shell interactions to obtain pair-distance distribution widths \ensuremath{\sigma} as a function of temperature. The temperature dependence of $\ensuremath{\sigma}(T)$ was accurately modeled using a correlated-Debye model for the lattice vibrational properties, suggesting Debye-like behavior in this material. Using this formalism, we obtain pair-specific correlated-Debye temperatures ${\ensuremath{\Theta}}_{\mathrm{cD}},$ of 110.7 $\ifmmode\pm\else\textpm\fi{}1.7 \mathrm{K}$ and $202.6\ifmmode\pm\else\textpm\fi{}3.7 \mathrm{K},$ for the Pu-Pu and Ga-Pu pairs, respectively. The result for the Pu-${\ensuremath{\Theta}}_{\mathrm{cD}}$ value compares well with previous vibrational studies on $\ensuremath{\delta}\ensuremath{-}\mathrm{Pu}.$ In addition, our results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, i.e, ${\ensuremath{\Theta}}_{\mathrm{cD}}$ for the Ga-Pu pair. Because the Debye temperature can be related to a measure of the lattice stiffness, these results indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu bonds. This effect has important implications for lattice stabilization mechanisms in these alloys.