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

Electrical resistivity, rho (T), measurements on U2Ru2Sn show typical Kondo semiconducting behaviour, namely a rho (T) similar to ln T behaviour at higher temperatures and an activation-like increase in p(T) below 20 K which indicates the opening of a small gap in the electronic density of states. The magnetic Susceptibility, chi (T), of U2Ru2Sn has a maximum around 180 K which is characteristic of intermediate-valence behaviour. The X (T) data for U2Ru2Sn have been fitted to the interconfigurational fluctuation model of Sales and Wohlleben giving a value of T-sf(*) = 155(2) K for the characteristic fluctuation temperature. Substituting as little as 5% Th for U leads to a p(T) variation reminiscent of that of a single-ion Kondo metal rho (T) = rho (0)[(1 - pi (2) 16) (T-2/ T-K(2))]. Values of T-K = 79(1) and 113(1) K are respectively obtained for alloys with 5% and 10% Th substitution.