HEAT DIFFUSIVITY OF THE MOTT SYSTEMS BACO0.9NI0.1S2-Y AND CUIR2S4

The thermal diffusivity D(T), the Seebeck-coefficient S(T) and specifi c heat capacity c(p)(T) of BaCo0.9Ni0.1S2-y and of CuIr2S4 were invest igated in the temperature range 100 K < T < 350 K and in particular th rough their metal-insulator transition at T-MI. We find steps in S(T), D(T) and in the heat conductivity kappa(T) at T-MI = 230 and 228 K, r espectively. In particular, for BaCo0.9Ni0.1S1.95, we find a step in k appa of almost one order of magnitude. Since a large pressure shift ha d been discovered earlier for BaCo0.9Ni0.1S1.9, these crystals are pot ential pressure activated heat switches.