Landau free energy for structural phase transitions in Pu

Depending on temperature, pressure and (Ga or Al) alloying plutonium undergoes a series of structural transitions. Based on crystallography and symmetry analysis of phonon modes, and relevant strain tensor components identified as order parameter, we develop a GinzburgLandau free energy for the FCC to simple monoclinic structural transition, δ → α, in Pu. We use the free energy to explore certain parts of the Pu phase diagram and relate the coefficients in the free energy expansion to experimental data such as specific heat and thermal expansion, Finally, we explore the role of intra-unit cell shuffle modes in this important transition.