Effect of high-pressure annealing on the normal-state transport of LaO0.5F0.5BiS2

We study normal state electrical, thermoelectrical, and thermal transport in polycrystalline BiS2-based compounds, which become superconducting by F doping on the O site. In particular, we explore undoped LaOBiS2 and doped LaO0.5F0.5BiS2 samples, prepared either with or without high-pressure annealing, in order to evidence the roles of doping and preparation conditions. The high-pressure annealed sample exhibits room temperature values of resistivity rho around 5 m Omega cm, Seebeck coefficient S around -20 mu V/K, and thermal conductivity kappa around 1.5 W/Km, while the Hall resistance R-H is negative at all temperatures and its value is -10(-8) m(3)/C at low temperature. The sample prepared at ambient pressure exhibits R-H positive in sign and five times larger in magnitude, and S negative in sign and slightly smaller in magnitude. These results reveal a complex multiband evolution brought about by high-pressure annealing. In particular, the sign inversion and magnitude suppression of R-H, indicating increased electron-type carrier density in the high-pressure sample, may be closely related to previous findings about change in lattice parameters and enhancement of superconducting T-c by high-pressure annealing. As for the undoped sample, it exhibits 10 times larger resistivity, 10 times larger vertical bar S vertical bar, and 10 times larger vertical bar R-H vertical bar than its doped counterpart, consistent with its insulating nature. Our results point out the dramatic effect of preparation conditions in affecting charge carrier density as well as structural, band, and electronic parameters in these systems.