Localization of 5f electrons in δ-plutonium: Evidence for the Kondo effect

Abstract

Among the actinides, plutonium is at the critical position between light actinides (up to plutonium) with itinerant 5f electrons and the heavy actinides (from americium on) with localized 5f electrons. The change of behaviour has been described by Johansson (Philos. Mag., 30 (19741 469) as a Mott-like transition of the 5f electrons between Pu and Am.However, in plutonium itself there is a huge volume expansion of 26% between the low temperature low symmetry α-phase and the high temperature high symmetry δ-phase.From the 20% expansion on going from α-Ce to γ-Ce, we infer a more important localization of 5f electrons in δ-Pu compared with the situation in α-Pu. Low temperature susceptibility measurements and high temperature resistivity measurements are analysed within a Kondo-like model of localized 5f electrons. High temperature susceptibility measurements of stabilized δ-Pu alloys have been made for the first time and it is found, in agreement with previous data and model, that a Curie-Weiss behaviour is recovered. This adds strong support to the hypothesis of 5f localization in δ-plutonium: the delocalization-localization transition of the 5f electrons along the actinide series starts in fact within the plutonium phase diagram, as also proposed by Antropov et al. (Sov. Phys. Solid State, 32 (1990) 1612) from band structure calculations.