Synthesis and thermoelectric properties of p-type Ba8Au xSi46-x clathrate

Abstract

Poly-crystalline Ba8AuxSi46-x clathrates were synthesized by the arc melting method and a subsequent annealing treatment. The as-synthesized sample contained some precipitates rich in Au at the grain boundaries, and the precipitates were reduced by annealing at 1000 °C. The Au content of the clathrate phase for the as-synthesized sample, Ba 7.4Au4.7Si41.3, was slightly lower than that for the stoichiometric composition, Ba8Au6Si40. In the annealed samples, the Au content of the clathrate phase increased with annealing time. These results indicated that Au can diffuse from Au-rich precipitates to the clathrate phase by annealing. The Seebeck coefficient of the as-synthesized and 1 hour annealed sample, Ba7.5Au 5.7Si40.3, were -80 and +100 μV/K at 500 °C, respectively. This suggested that the carrier type was changed by the Au content in the clathrate. In the samples annealed for longer than 1 hour, the Seebeck coefficient decreased with annealing time. This indicated that the hole carrier concentration increased in excess because of overdoping due to the diffusion of Au. © Published under licence by IOP Publishing Ltd.