La impurity effects on quadrupolar ordering in PrPb₃

We study low-temperature properties of Pr_1-xLa_xPb₃ with the ground state of a non-Kramers Γ₃ for 0≤x ≤0.8. From the concentration dependence of the specific heat, quadrupolar ordering is expected to occur only up to x∼0.02. For a wide range of La concentrations where the ordering is absent, the specific heat shows a T linear variation, which is in an excellent agreement with the result obtained by the model for amorphous materials with a random configuration of a two-level system. Impurity effects on quadrupolar moments will be discussed.