Transport properties of Bi-doped FeSe superconductor up to 700 K

Polycrystalline samples of Fe1-xBixSe with x = 0.00, 0.02, 0.05, and 0.08 are prepared by conventional solid state reaction. The resistivity and therniopower are measured up to 700 K. The onset superconducting transition temperature decreases slightly with increasing Bi content. Transport behavior of electrical resistivity in the normal state is quite complex. A linear temperature dependence is found between 20 and 100K. Above 150K, the electrical resistivity behavior resembles misfit-layered cobalt oxides Ca₃Co₄O₉+ς<$; a Fermi-liquid behavior of T² dependence is observed between 150 and 2I0K with the Fermi-liquid transport coefficient A having the size between 4.3 × 10 ^-6and 10× 10^-6 ' mΩ-cm/K², followed by an incoherent metal and a high-temperature nonmetal-Iike behavior. Therniopower behavior is nonconventional. Sign crossover of therniopower occurs both below and above room temperature. According to the dynamical mean field calculations, the negative dip feature of therniopower between 110 and I30K seems to be associated with excitations of a pscudogap ground state.