Low-temperature properties of the dilute quadrupolar system Pr _xla_1-xPb₃

We have studied the low-temperature properties of Pr_xLa _1-xPb₃ with the ground state of a non-Kramers Γ ₃ doublet for the Pr concentration for 0≤x≤1. From the concentration dependence of the specific heat, the quadrupolar ordering, which is observed at T_Q = 0.4 K in PrPb₃, is concluded to persist only for x∼0.98. For a wide range of Pr concentration for 0.1≤x≤0.95, the specific heat shows a T-linear variation below 0.5 K with a large coefficient, which is almost reproduced by the model for amorphous materials with a random configuration of two-level system. For x≤0.05, C/T shows a non-Fermi liquid behavior with the monotonous enhancement of C/T with decreasing temperature, which is probably caused by Kondo effect arising from the correlation between the Γ₃ moments and the conduction electrons.