Thermal conductivity and lorentz number of the "golden" phase of the Sm1-xGdxS system with homogeneous variable valence of samarium

The thermal conductivity and electrical resistivity are measured in the tem perature range 160-300 K for two compositions of the "golden" phase of the Sm1- xGdxS system with x = 0.14 and 0.3, in which a homogeneous variable va lence of samarium ions is observed. It is found that, in this temperature r ange, the experimentally obtained Lorentz number L appearing in the electro n component of thermal conductivity for these compositions exceeds the theo retical Sommerfeld value L-0 = 2.45 x 10(-8) W Omega/K-2 typical of metals and highly degenerate semiconductors. It is also proved that the value of L increases with temperature in the interval 160-300 K starting from 160 K. A theoretical model capable of explaining the obtained experimental results is discussed. (C) 2000 MAIK "Nauka/Interperiodica".