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 thermopower 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 100 K. Above 150 K, the electrical resistivity behavior resembles misfit-layered cobalt oxides Ca3Co4O9+δ; a Fermi-liquid behavior of T2 dependence is observed between 150 and 210 K with the Fermi-liquid transport coefficient A having the size between 4.3 × 10−6 and 10 × 10−6 mΩ-cm/K2, followed by an incoherent metal and a high-temperature nonmetal-like behavior. Thermopower behavior is nonconventional. Sign crossover of thermopower occurs both below and above room temperature. According to the dynamical mean field calculations, the negative dip feature of thermopower between 110 and 130 K seems to be associated with excitations of a pseudogap ground state.