We have synthesized single crystalline Ba8AlxSix-46 clathrates by using the flux Czochralski (CZ) method with Al-rich melt. The specific electric resistivity, the Seebeck coefficient and the power factor of single crystalline Ba8Al14Si32 were 0.73 mΩcm,70.0μV/K and 6.8×10-4 V2/K2Ωm, respectively. These values are higher than that of single crystalline Ba8Al12Si34 clathrate because of the reduced carrier concentration. It is indicated that Al contents and the carrier concentration of single crystalline Ba8AlxSi46-x can be controlled by using the flux Czochralski method.
Poly-crystalline Ba8Cu6Ag2Si38 clathrates were synthesized by the arc-melting method and a subsequent annealing treatment. The main phase of all the samples was type-I clathrate. However, there were some precipitates which rich in Cu, Ag or Si in the grain boundary of the as-synthesized sample and the precipitates gradually reduced with the increase of annealing time. The transition metal content in the clathrate increased with the annealing time because of the diffusion of the Cu and Ag atoms from precipitates phase into clathrates phase. The as-synthesized sample was n-type material. For the 576 hours annealed sample, the carrier type changed from n-type to p-type because of the increase of Cu and Ag content in the clathrate.
View the article online for updates and enhancements. 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 7.4 Au 4.7 Si 41.3 , was slightly lower than that for the stoichiometric composition, Ba 8 Au 6 Si 40 . 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, Ba 7.5 Au 5.7 Si 40.3 , were -80 and +100 V/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.
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