Extended x-ray absorption fine structure spectroscopy (EXAFS) is used to investigate the local atomic environment and vibrational properties of plutonium and gallium atoms in the ${\alpha }^{\prime }$ and δ phases of a mixed phase Pu-Ga alloy. EXAFS results measured at low temperature compare the structure of the mixed phase sample with a single-phase δ-Pu sample. EXAFS spectral components attributed to both ${\alpha }^{\prime }-\mathrm{Pu}$ and δ-Pu were observed in the mixed phase sample. Ga K-edge EXAFS spectra indicate local atomic environments similar to the Pu $L_{\mathrm{III}}-\mathrm{e}\mathrm{d}\mathrm{g}\mathrm{e}$ EXAFS results, which suggests that Ga is substitutional for Pu atoms in both the monoclinic ${\alpha }^{\prime }-\mathrm{Pu}$ and the fcc δ-Pu structures. In δ-Pu, we measure a Ga-Pu bond length contraction of 0.11 Å with respect to the Pu-Pu bond length. The corresponding bond-length contraction around Ga in ${\alpha }^{\prime }-\mathrm{Pu}$ is only 0.03 Å. Results from temperature-dependent Pu $L_{\mathrm{III}}-\mathrm{e}\mathrm{d}\mathrm{g}\mathrm{e}$ EXAFS measurements are fit to a correlated Debye model, and a large difference in the Pu-Pu bond Debye temperature is observed for the ${\alpha }^{\prime }$ and δ phases: ${\theta }_{\mathrm{cD}}\left({\alpha }^{\prime }\right)=159\mathrm{}\pm 13\mathrm{K}$ versus ${\theta }_{\mathrm{cD}}\left(\delta \right)=120\mathrm{}\pm 3\mathrm{K}.$ The corresponding analysis for the Ga K EXAFS determines a Ga-Pu bond Debye temperature of ${\theta }_{\mathrm{cD}}\left(\delta \right)=188\mathrm{}\pm 12\mathrm{K}$ in the δ-Pu phase. These results are related to the observed solubility of Ga in δ-Pu, the “stabilization” of δ-Pu by Ga at room temperature, and the insolubility of Ga in ${\alpha }^{\prime }-\mathrm{Pu}.$

• Received 12 February 2003

DOI:https://doi.org/10.1103/PhysRevB.67.224206