Fabrication of Bi₂Te_{3− x} Se _x nanowires with tunable chemical compositions and enhanced thermoelectric properties

Uniform Bi₂Te_{3− x} Se _x nanowires (NWs) with tunable components are synthesized by a modified solution method free of any template, and inter-diffusion mechanism is proposed for the growth and transformation of ternary nanowires. Spark plasma sintering is adopted to fabricate the pellets of Bi₂Te_{3− x} Se _x NWs and thermoelectric transport properties are measured. As compared to Bi₂Te₃ pellets, Se doping results in lowered electrical conductivity because of the reduced carrier concentration, both the Seebeck coefficient and the power factor are enhanced substantially. The Bi₂Te_2.7Se_0.3 pellet exhibits the highest power factor at room temperature as a result of optimized carrier concentration (4.37 × 10¹⁹ cm⁻³) and mobility (60.22 cm² V⁻¹ s⁻¹). As compared to Bi₂Te₃, the thermal conductivity of Bi₂Te_{3− x} Se _x is lowered owing to the enhanced phonon scattering by dopants and grain boundaries. As a result, the ZT value at 300 K is substantially improved from 0.045 of Bi₂Te₃ to 0.42 of Bi₂Te_2.7Se_0.3. It is suggested that Se doping is an effective way to enhance the thermoelectric performance of Bi₂Te₃ based materials. (paper)