How the Kondo effect stabilises delta-phase plutonium

My purpose in this paper is to find the underlying electronic cause of the observed thermodynamic stabilisation of δ-phase plutonium. I present a simple model demonstrating that the valence fluctuations found in δ-phase are essential for stabilising this phase. I make two explicit comparisons of the temperature dependencies of the available heat capacity data: one of α-phase Pu versus δ-phase Pu, and the other of α-Pu versus an artificial δ-phase model which includes only lattice vibrations and a free-electron term. These comparisons strongly suggest that delta phase is stabilised – both at high and low temperature – by the entropy of the valence fluctuations which are present in this phase.