Quadrupolar ordering of 5f electrons in UCu2Sn

A huge softening of the transverse elastic modulus C-66 has been found in U Cu2Sn around a phase transition point at similar to 16 K. In addition to th e elastic moduli, the specific heat and x-ray diffraction were measured for polycrystals and single crystals in order to elucidate the origin for the transition. All anomalies obtained in the thermodynamic properties were ana lyzed by assuming a localized 5f(2) configuration in the hexagonal symmetry . It is revealed that the transition originates from a quadrupolar ordering of the non-Kramers ground doublet Gamma(5).