New Pseudophase Structure for $\alpha \mathrm{\text{−}}\mathrm{P}\mathrm{u}$

We propose a new pseudophase crystal structure, based on an orthorhombic distortion of the diamond structure, for the ground-state $\alpha$ phase of plutonium. Electronic-structure calculations in the generalized-gradient approximation give approximately the same total energy for the two structures. Interestingly, our new pseudophase structure is the same as the $\gamma$-Pu structure except with very different $b/a$ and $c/a$ ratios. We show how the contraction relative to the $\gamma$ phase, principally in the $z$ direction, leads to an $\alpha$-like structure in the $[0,1,1]$ plane and reproduces the short range bonds of the $\alpha$ phase. This is an important link between two complex structures of Pu and opens new possibilities for exploring the very rich phase diagram of Pu through theoretical calculations.

Figure 1

DOS for $\alpha$ Pu, pseudo-$\alpha$, and $\gamma$ Pu, and Crocker’s structure, calculated at the theoretical equilibrium volume.

Figure 2

Distorted diamond structure (pseudo-$\alpha$) in the (011) direction. The blue atoms are the eight positions in the $\alpha$ structure.