Preparation and thermoelectric properties of annealed CoSb and CoSb2 thin films deposited through RF co-sputtering

Co-Sb-based compounds have been established as promising materials for applications at intermediate temperatures. In this study, the structural, electrical, and thermoelectric properties of CoSb and CoSb2 thin films are presented and discussed. A series of Co-Sb-based thin films were prepared via RF co-sputtering on an oxidized silicon substrate at room temperature. CoSb2-phase thin films were amorphous in the as-deposited state; all films were post-annealed at 300 degrees C to obtain crystalline structures. High-temperature X-ray diffraction patterns indicated that the CoSb2 crystallized at temperatures of 100-150 degrees C. The annealed crystalline films contained phases in conformance with the phase diagram and had distinct microstructures. The electrical and thermoelectric properties were measured as a function of temperature, and variations were interpreted in terms of the identified phases, defect concentrations, and possible conduction mechanisms. The CoSb and CoSb2 phases had much lower electrical resistivities than the widely reported CoSb3 skutterudite phase, which coupled with high Seebeck coefficients gave high power factors. All of the samples were n-type conductors at the temperatures of maximal performance. We report maximum power factors of 5 and 8.47 mWm(-1) K-2 for the CoSb and CoSb2 thin films, respectively. (C) 2016 Elsevier B.V. All rights reserved.