抄録
Temperature dependence of the elastic constants in a series of rare earth hexaborides has been investigated by means of the ultrasonic method. The remarkable softening of the transverse C44 mode in PrB6, NdB6, DyB6 and HoB6 has been discussed in connection with the cooperative Jahn-Teller effect due to the CEF ground state degenerated by the quadrupolar moment. The low temperature behavior of C44 in CexLa1-xB6 compounds is presented to show the Kondo effect on the quadrupolar moment of Γ8 ground state. The anomaly of the bulk modulus CB in SmB6 is related to the valence fluctuation state in the system.
