Valence fluctuation in Eu compounds: Role of charge screening

Observed valence states of various europium intermetallic compounds exhibit a systematic trend. They can be classified into two groups, i.e., intermetallics of strong $d$ character at the Fermi level and $s$-like band intermetallics. Among the latter, ${\mathrm{Eu}}^{2+}$ is the only stable configuration. The role of the $d$- or $s$-like character of band structure of the compounds is discussed with respect to the stabilization of the various Eu configurations within a one-center picture. Charge screening plays a dominant role in this process. This discussion bears on the physics of fluctuating-valence systems, as well as on the electronic structure of various classes of intermetallic compounds. A numerical analysis is performed considering a Moriya-like model density of states to describe the conduction states of the Eu compound. One illustrates the role of screening in the crossover between the two europium configurations in $\mathrm{Eu}{\left(A_{1-x}{B}_x\right)}_2$ intermetallic compounds. Effects connected with temperature are also briefly discussed within our picture.