The effect of Th substitution and of magnetic field on Kondo semiconducting behaviour in U₂Ru₂Sn

Electrical resistivity, ρ(T), measurements on U₂Ru₂Sn show typical Kondo semiconducting behaviour, namely a ρ(T) ∼ 1n T behaviour at higher temperatures and an activation-like increase in ρ(T) below 20 K which indicates the opening of a small gap in the electronic density of states. The magnetic susceptibility, χ(T), of U₂Ru₂Sn has a maximum around 180 K which is characteristic of intermediate-valence behaviour. The χ(T) data for U₂Ru₂Sn have been fitted to the interconfigurational fluctuation model of Sales and Wohlleben giving a value of T_sf* = 1552(2) K for the characteristic fluctuation temperature. Substituting as little as 5% Th for U leads to a ρ(T) variation reminiscent of that of a single-ion Kondo metal ρ(T) = ρ(0)[1 - (π²/16)(T²/T_K²)]. Values of T^K = 79(1) and 113(1) K are respectively obtained for alloys with 5% and 10% Th substitution.