On the effect of carbon nanotubes on the thermoelectric properties of n-Bi2Te2.4Se0.6 made by mechanical alloying

Composite materials based on n-Bi2Te2.4Se0.6 with commercial multi walled carbon nanotubes (MWCNTs) have been synthesized via high energy ball milling and spark plasma sintering. The effect on the transport properties of the presence of MWCNTs during the ball billing step is studied. It is demonstrated that MWCNTs, even in small quantity, change dramatically the transport properties. Seebeck coefficient, electrical resistivity, thermal diffusivity and carrier concentration are measured and their variation discussed. The presence of MWCNTs during the ball milling step is discussed as it clearly induces three competing effects, the presence of tellurium vacancy, the decreased grain size of Bi2Te2.4Se0.6 either promoted during the ball milling or result of the a prevented grain growth during the sintering and a n-type doping. The large carrier concentration variation caused by the MWCNTs represents an alternative way of tuning the transport properties.