Plutonium chalcogenides: Intermediate valence and electronic structure

Abstract

The rocksalt-structure Pu chalcogenides show a series of puzzling physical properties that cannot be understood by an integer-valent 5f ground state of the Pu ion. However, a simple intermediate valent state between di- and trivalency seems to be ruled out by the lattice constant, which is less than that of the hypothetical ${\mathrm{Pu}}^{3+}$ or ${\mathrm{Pu}}^{2+}$ chalcogenides. We propose in this paper that the anomalous properties of the Pu chalcogenides can be consistently understood by taking the compounds as the high-pressure, collapsed intermediate valent phase of the corresponding Sm chalcogenides for which they have the same f occupation number. The temperature-independent magnetic susceptibility, the temperature dependence of the resistivity, the neutron scattering, the specific heat, and the compressibilities can thus be consistently explained.