Magnetic moment, thermal and electrical transport in the inverse Mott systems BaCo0.9Ni0.1S2-y and CuIr2S4

The antiferromagnetic BaCo0.9Ni0.1S2-y and the paramagnetic CuIr2S4 Mott sy stems show an inverse conductivity behavior, i.e., the metallic phase occur s at low or high temperatures, respectively, which also suggests inverse be havior in other transport properties. In this contribution we present magne tization data, conductivity, thermal conductivity, and Seebeck effect in th e temperature range 4.2 K < T < 350 K and in particular through the metal-i nsulator transition at T-MI. We recover the anomalies in chi(T), sigma(T), which are discussed using Jahn-Teller and anti-Jahn-Teller models; also, we compare the anomalies in sigma(T), S(T), and of the heat conductivity K(T) at T-MI. In particular, for BaCo0.9Ni0.1S1.95, we find a step in kappa of almost one order of magnitude (times 6) and a large pressure shift, less th an or equal to -24 K/kbar, which makes this material a potential pressure a ctivated heat switch, while CuIr2S4 shows a small step of kappa (times 1.2) and a pressure shift of +2.8 K/bar. (C) 1998 American Institute of Physics . [S0021-8979(98)40211-1].