Influence of Crystallinity on the Electrical Property of KFe(S1-xSex)2

The electrical properties of KFe(S1- x Se x )2 (0≤x≤0.89) were studied on crystals annealed for a long period. The resistivity ρ along the c-axis shows high values: 1.6×104 Ω·cm for x=0 and 8.6×101 Ω·cm for x=0.89 at 290 K. The nonmetallic temperature-dependent resistivity is approximated by ρ∝exp [(T 0/T)1/2], where T 0 is a constant. Both the susceptibility and the Seebeck coefficient show metallic behavior. Observations using a transmission electron microscope indicate that the specimens consist of many grains. It is concluded that these compounds are essentially metallic. The high resistivity and the nonmetallic temperature dependence are ascribed to the imperfections in the crystal.