Vibrational properties of Ga-stabilized δ-Pu by extended x-ray absorption fine structure -: art. no. 214107

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 K. EXAFS data were acquired at both the Ga Kedge and the Pu L-III edge. Curve fits were performed to the first shell interactions to obtain pair-distance distribution widths sigma as a function of temperature. The temperature dependence of 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 Theta(cD), of 110.7 +/-1.7 K and 202.6+/-3.7 K, for the Pu-Pu and Ga-Pu pairs, respectively. The result for the Pu-Theta(cD) value compares well with previous vibrational studies on delta-Pu. In addition, our results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, i.e, Theta(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.