Intermediate-valence behavior is sometimes observed in lanthanide-based materials containing Ce, Yb, Sm or Eu. However, the number of actinide-based systems that exhibit this type of behavior is rather limited. In this work, we present the discovery and characterization of a uranium compound U2Rh2Sb, which turns out to be a candidate for the intermediate-valencebehavior. The material shows a characteristic feature in the magnetic susceptibility around T = 50 K, which can be described within the interconfiguration-fluctuation model of intermediate valence systems. We find the energy difference between the 5f3(U3+) and 5f2(U4+) states to be δEex/kB ≈ 400 K and the corresponding valence fluctuation temperature to be Tvf ≈ 140 K. The value of the electronic specific heat coefficient γ = 50 mJ mol-1 U K-2 signals a modest electron effective mass enhancement. The electrical resistivity indicates metallic behavior, albeit with a small residual resistivity ratio. Measurements of thermoelectric properties indicate a change of sign in the Seebeck coefficient around T = 100 K, with a minimum achieved at T = 50 K, which coincides with the broad peak observed in magnetic susceptibility. The experimental results are compared with the theoretical analysis, based on the first-principles calculations, including lattice dynamics.
@article{arxiv.2507.10720,
title = {Intermediate-valence behavior in U2Rh2Sb},
author = {D. Legut and M. Krnel and P. Koželj and Yu. Prots and M. Juckel and U. Burkhardt and A. Ormeci and Yu. Grin and A. Leithe-Jasper and J. Kolorenč and E. Svanidze and U. D. Wdowik},
journal= {arXiv preprint arXiv:2507.10720},
year = {2025}
}