Divergence of the very-low-temperature residual resistivity of TmxSe as x→1

The resistivity of the intermediate-valence compounds TmxSe (0.79<x<0.993) has been measured down to 10 mK. The variation of the residual resistivity with composition (i.e., with the proportion of Tm2+) suggests that a perfectly stoichiometric system might become insulating at 0 K. This divergence seems to take place when the two valence states are equal in concentration. A possible interpretation based on the recent developments of the Kondo-lattice models is discussed. © 1979 The American Physical Society.