  The analysis of the properties of rare-earth based materials relies on the
Crystalline Electric Field theory. This theory has to be reconsidered in case
of cage-type compounds, where the rare-earth ion can substantially depart from
its, high symmetry, average position. It is shown that, in case of an orbital
degeneracy at the cage center, a specific Jahn-Teller effect develops in the
paramagnetic range: at low temperature, the distribution of the magnetic ion
spreads inside the cage, the magnetic entropy is reduced, whereas the cage
multipolar susceptibilities are increased. These consequences are put in
relation with the properties of some metallic rare-earth cage compounds.
