Synthesis of N-type Bi2Te2.7Se0.3 Compounds through Oxide-Reduction Process and Related Thermoelectric Transport Properties

SnSe2 alloys have been investigated in recent times as potential n-type thermoelectric materials. In this study, the thermoelectric transport properties of a series of Sb-doped SnSe2, Sn(Se1-xSbx)2 (x = 0, 0.015, 0.03, 0.045, 0.06) alloys are investigated. The electrical conductivity was generally enhanced with Sb doping owing to a large increase in electron concentration. However, the Seebeck coefficient largely decreased with doping. Consequently, the power factor was significantly lower at a low doping of x = 0.015, and then began rising as the doping was increased beyond x = 0.015. It was found that the density-of-states effective mass and weighted mobility decreased with Sb doping, implying that the electrical transport properties of SnSe2 were degraded by Sb doping. The total and lattice thermal conductivities gradually decreased due to additional point defect scattering. Thus, the thermoelectric figure of merit declined significantly, from 0.30 of the pristine sample with a low doping of Sb (x = 0.015) at 750 K, to 0.18, and then for x = 0.06 it gradually recovered to the value of the undoped sample. The thermoelectric quality factor decreased as the Sb doping was increased, implying that Sb doping did not enhance the thermoelectric transport properties, despite the large increase in electron concentration.

Section: Introductionmentioning

confidence: 99%

Thermoelectric Transport Properties of Sb-doped SnSe2 Polycrystalline Alloys

Kang,

Rho,

Cho

et al. 2023

Optimization of Sintering Temperature for the Synthesis of n-type Mg3SbBi0.99Te0.01 Thermoelectric Materials

Joo,

Son,

Jang

et al. 2023

Mg3Sb2-based materials are promising candidates to replace n-type Bi2Te3 for cooling and power generation at low temperatures. Generally, the thermoelectric performance of a material is sensitively affected by synthesis process parameters, and among them, sintering temperature (Ts) is a critical one. In this study, n-type Mg3SbBi0.99Te0.01 polycrystalline samples were fabricated by mechanical alloying and spark plasma sintering (SPS), and the effects of varying Ts (923 – 1073 K) on the thermoelectric properties were investigated. Sintering Mg3SbBi0.99Te0.01 at an elevated temperature of 1073 K resulted in a notable increase in electrical conductivity at low temperatures below about 423 K. This is ascribed to a sharp reduction in carrier scattering by ionized impurities. For the same reason, the carrier mobility increased sharply at a Ts of 1073 K, which is a critical temperature for sintering in this study. Moreover, the Seebeck coefficient increased and thermal conductivity decreased simultaneously by raising Ts, resulting in the maximum power factor (PFmax) of 2.2 × 10-3 W m-1K-2 and the maximum dimensionless figure of merit (zTmax) of 1.20 in the sample sintered at 1073 K. Therefore, when Ts was raised from 923 K to 1073 K, the PFmax and zTmax increased by 29 % and 64 %, respectively. This improvement in performance is attributed to the annihilation of defects generated during the mechanical alloying process, which was confirmed by microstructure analysis by transmission electron microscopy (TEM).

Electronic Transport Properties of Bi2Te2.7Se0.3 Fabricated by Hot Extrusion

Hwang¹,

Hasan²,

Lee³

2023

Herein we report the optimized processing conditions of hot extrusion for fabricating an n-type Bi2Te2.7Se0.3 thermoelectric compound, with high electronic transport properties as well as improved mechanical reliability. We fabricated a Bi2Te2.7Se0.3 extrudate that was 3.8 mm in diameter and 700 mm in length by controlling the processing parameters of temperature and pressure. A 3-point bending strength of over 70 MPa, which is 7 times higher that of the commercial zone melting ingot, was obtained in the samples prepared at 460 oC temperature under 6–6.5 MPa pressure. The samples benefitted from the formation of a highly-dense microstructure (relative density > 98%). It is noted that the electronic transport properties (electrical conductivity and Seebeck coefficient) could be manipulated by controlling the applied pressure of hot extrusion at 460 oC, mainly due to the change in the characteristics of the 00l crystal orientation, which originated from grain rotation and rearrangement. Power factor values of ~2.9 mW/mK2 at 300 K and ~2.95 mW/mK2 at 320 K, similar to those of sintered bulks, were obtained in the hot extrudate fabricated under processing parameters of 460 oC and 6 MPa. Moreover, a high power factor value of 2.25 mW/mK2 was observed even at the high temperature of 480 K, which is 70% higher than that of Bi2Te2.7Se0.3 bulk fabricated by hot pressing.