Electron transport phenomena in NiS2-xSex single crystals

Structural studies, electrical resistivity, and Seebeck coefficient measurements are reported in the range 4.2 - 300 K for single crystals of NiS2-xSex (0 less than or equal to x less than or equal to 0.71) grown from a Te melt. Over the entire temperature and composition ranges there are no large scale structural changes concomitant to a variety of magnetic ordering phenomena, and to a changeover from insulating to metallic characteristics as x increases. Thus, the evolution in transport characteristics with x can be studied without interference from the lattice; moreover, the electron count is unaffected by substitution of Se for S. The existence of anomalous peaks in resistivity as a function of temperature is attributed to significant electron correlation phenomena which allow the entropy of charge carrier to play a dominant role. The complex temperature dependence of the Seebeck coefficient is attributed to the participation of both electrons and holes in charge transport.