Thermal conductivity and Lorenz number of the Ce1−xLaxNiAl4 Kondo alloys

• Dominance of the electronic thermal conductivity in Ce1−xLaxNiAl4.
• Temperature dependent Lorenz number.
• Invalidity of the Wiedemann–Franz law at low temperatures.
• Effect of the magnetic field on the thermal conductivity above 30 K.

The temperature dependence of the thermal conductivity (κ) for Ce1−xLaxNiAl4 alloys has been studied. In comparison to LaNiAl4, the substitution of La by Ce reduces the κ values. The behaviour of the Lorenz number L in the Kondo alloys Ce1−xLaxNiAl4 differs considerably both in magnitude and in temperature dependence from L characteristic of pure metals. The Lorenz number of Ce1−xLaxNiAl4 exhibits positive values and peaks at low temperatures. The obtained values of L at low temperatures are higher than the theoretical value of L0. The reason for the increased Lorenz number may be the contribution of phonons, Kondo and crystal electric field (CEF) effects. The values of L/L0 are close to 1 at high temperatures, which is in agreement with the conclusion that the electronic part κe(T) dominates at high temperatures. Such a temperature dependence of L/L0 is commonly observed in Kondo compounds. Applying an external magnetic field has no significant effect on the thermal conductivity below 30 K. Above this temperature a gentle changes of κ can be observed.