UC Irvine

We report the results of resistivity measurements on Ce0.9-xLaxTh0.1 alloys for x=0.10,0.11,0.14, and 0.17 in the temperature interval 4.2-300 K and for the pressure range 0-12 kbar. Using these results we have semiquantitatively determined the P-T phase boundary for the isomorphic - phase transition for each concentration x. For x=0.10,0.11, and 0.14 the transitions are continuous at zero pressure, first order for pressures within the interval PcL(x)Pcu(x). Hence, for these concentrations the phase boundaries terminate at two critical points. For x=0.17, all observed transitions are continuous. Hence, in x-P-T space the surface of first-order transitions terminates at a critical edge (Tc(x),Pc(x)) such that, over an interval of x,Pc(x) is double valued and such that there is a "critical inflection point." These unusual features can be understood qualitatively as following from very general Fermi-liquid properties of the cerium 4f electronic system, together with the dilution and negative-pressure effects of alloying with lanthanum. We show that this qualitative description is consistent with existing experimental data. © 1984 The American Physical Society.