Neutron scattering studies of intermediate-valence compounds

Recent progress in the study of unstable valence compounds by inelastic neu tron scattering is discussed. Deeper understanding of the ground state of S m-based mixed valence compounds results from powder and single-crystal neut ron spectroscopy of Sm spin-orbit transitions in a wide energy range. "Spin -gap" systems with a complicated spectral shape of the magnetic response at low temperature have been found among Ce- and Yb-based compounds, They can be considered as a separate group among unstable valence systems: both cry stal field effects and hybridization with conduction electrons appears to b e sizable and of comparable magnitude. In heavy fermion compounds the inter play of crystal field interactions and hybridization effects in a relativel y large temperature range appears to be an important Factor for the Formati on of the magnetic excitation spectra. Pronounced anomalies have been disco vered in the lattice dynamics of the intermetallic system Ce-Ni in relation with the intermediate valence state of Cc. (C) 2000 Elsevier Science B.V. All rights reserved.