ABSTRACT
Since the discovery of its extraordinary thermoelectric properties, bismuth-telluride (Bi2Te3) has become a vital component for thermoelectric industry [1-3]. Bulk Bi2Te3 materials are known to have some of the highest thermoelectric œgure of merit, ZT ~ 1.14 at room temperature (RT). še thermoelectric œgure of merit is deœned as ZT = S2σT/K, where S = −ΔV/ΔT is the Seebeck coe²cient (ΔV is the voltage di¤erence corresponding to a given temperature di¤erence ΔT), σ is the electrical conductivity, and K is the thermal conductivity, which has contributions from electrons and phonons. It is clear from ZT deœnition that in order to improve thermoelectric œgure of merit one should increase S2σ and decrease the thermal conductivity. Di¤erent approaches have been tried in order to enhance the thermoelectric properties of bulk Bi2Te3 or its alloys. šese approaches included the composition change from its stoichiometry, the use of polycrystalline materials with di¤erent grain sizes, intentional introduction of structural defects and incorporation of di¤erent dopants, for example, Sb or Se, into Bi2Te3 lattice. še optimization of bulk Bi2Te3 led to incremental improvements but no breakthrough enhancement in ZT was achieved. More promising results (ZT ~ 2.4 for p-type material at RT) were achieved with Bi2Te3/Sb2Te3 superlattices produced by low-temperature deposition [4]. A recent study indicated that the low-dimensional structuring of BiSbTe alloys [5] also allows for ZT enhancement to ~1.5 at RT. But still higher ZT values are needed for major practical impact. It has been shown that ZT above 3 or 4 at RT are needed in order to make thermoelectric cooling and power generation competitive with conventional methods [6].
