Pressure effects of quadrupolar system Pr_xLa _1-xPb₃ for x=1 and 0.97

We have studied the pressure dependence of the specific heat for PrPb ₃ and La-diluted system Pr_o.97La_o.o3Pb ₃. In PrPb₃, the quadrupolar ordering temperature at Tq=0.4 K rises by δT=10 mK at P=0.66 GPa. In Pr_0.97La _0.03Pb₃, in which the quadrupolar ordering disappears by the La substitution, the specific heat C varies with increasing pressure. C/T below 0.3 K is nearly constant at low pressures, while C/T increases gradually with decreasing temperature at P=0.88 GPa. These results can be explained by the pressure dependence of the intersite interaction between the Γ₃ moments and that of the interaction between the rΓ₃ moments and the conduction electrons.