Electronic transport in thermoelectric YbzCo4Sb12 skutterudite thin films studied by resistance noise spectroscopy

Abstract

Skutterudites CoSb3 are considered interesting candidates for thermoelectric applications, because the filling of guest atoms into the cage-like structure has the potential to improve its thermoelectric properties by an increased phonon scattering, which reduces the thermal conductivity. This, however, requires that a high electrical conductivity is maintained. In this study, we performed resistivity, Hall effect, and fluctuation spectroscopy measurements on polycrystalline thin films of semiconducting YbzCo4Sb12 with 0<z<0.27. Our aim is to better understand the conventional dc electronic transport but also the low-frequency dynamical properties of the charge carriers. The electronic properties are highly sensitive to the filling factor z as well as other parameters, e.g., the Sb content. The resistivity can be described by Mott variable range hopping at low temperatures. A large 1/f noise level suggests an influence of the granularity of the polycrystalline thin films. By analyzing the 1/f-noise and two-level fluctuations, which are abundant for filled samples annealed at 500 °C, we are able to determine the energy distribution of the relevant electronic switching processes. A likely explanation for the observed low-frequency dynamics is capture/emission processes of impurities with a broad distribution within the energy gap.