Enhancement in power factor of Sn and Zn co-doped Bismuth Telluride for thermoelectric applications

Abstract

The powdered samples of pure and Sn-Zn co-doped Bi₂Te₃ were synthesized using the solvothermal method at 200 °C. XRD analysis provided information regarding hexagonal crystal structure and space group R-3 m. The lattice parameters were obtained from Rietveld refinement which shows a decrease after Sn-Zn co-doping. The variation in lattice strain, dislocation density and stacking faults provides information regarding the presence of defects in samples. FESEM confirms the hexagonal plate-like morphology of the synthesized samples. The length of synthesized hexagonal nanoplates was in the range of 70–270 nm and the thickness was in the range of 10–20 nm. EDS spectra provided the elemental composition for all samples. Raman spectroscopy confirms the presence of three vibrational modes \({\text{A}}_{1\text{g}}^{1}\), \({\text{E}}_{\text{g}}^{2}\) and \({\text{A}}_{1\text{g}}^{2}\) in the samples. XPS was used to obtain the chemical states of the elements present in the samples. Hall measurement provided the carrier concentration in the range of 1.126 × 10¹⁸—7.168 × 10¹⁸ cm⁻³ and mobility in the range of 110–71 cm²/Vs at room temperature. The electrical conductivity of Sn-Zn co-doped samples was increased with increasing doping content and the highest electrical conductivity of 0.658 × 10² S/cm was obtained for Sn_0.03Zn_0.03Bi_1.94Te₃ sample at 473 K. The highest value of Seebeck coefficient was observed in the pure sample which is -148.746 μV/K at room temperature. The value of power factor was calculated from electrical conductivity and Seebeck coefficient which shows that the highly doped sample Sn_0.03Zn_0.03Bi_1.94Te₃ has the highest value of power factor which is 0.628 × 10^–5 Wm⁻¹ K⁻² at room temperature which can enhance figure of merit.