RESUMEN
Lead-free manganese telluride has been considered to be a promising candidate for mid-temperature thermoelectric materials. In this work, we report point defect scattering-induced reduction of thermal conductivity in MnTe with Se alloying, fabricated by a facile method combining mechanical alloying and spark plasma sintering. A low lattice thermal conductivity of 0.56 W/mK was obtained for MnTe0.92Se0.08, which is quite close to the amorphous limits. A detailed Debye model analysis reveals the underlying mechanism of phonon scattering and well predicts the thermal conductivity with different contents of Se. Meanwhile, a slight increase of carrier concentration was also observed after Se alloying, accompanied by a variation of energy gap that may be associated with the competition among anions in trapping charges. Further Na doping leads to enhanced electrical transport properties, achieving a maximum ZT value of 1.03 at 873 K. An average ZT of 0.52 and a calculated efficiency of more than 9% also suggest the promising application of MnTe at medium temperatures.
RESUMEN
Intrinsic Bi2Te3 is a representative thermoelectric (TE) material with high performance at low temperature, which enables applications for electronic cooling. However, antisite defects easily form in p-type Bi2Te3, resulting in the difficulty of further property enhancement. In this work, the formation energy of native point defects in Bi2Te3 supercells and the electronic structure of Bi2Te3 primitive unit cell were calculated using first-principles. The antisite defect Bi_Te1 has a lower formation energy (0.68 eV) under the Te-lack condition for p-type Bi2Te3. The effects of point defects on TE properties were investigated via a series of p-type Bi2Te3-x (x = 0, 0.02, 0.04, 0.06, 0.08) single crystals prepared by the temperature gradient growth method (TGGM). Apart from the increased power factor (PFâ¥) which originates from the increased carrier concentration (n â¥) and m*, the thermal conductivity (κ â¥) was also cut down by the increased point defects. Benefitting from the high PF⥠of 4.09 mW m-1 K-2 and the low κ ⥠of 1.77 W m-1 K-1, the highest ZT ⥠of 0.70 was obtained for x = 0.06 composition at 300 K, which is 30% higher than that (0.54) of the intrinsic Bi2Te3.
RESUMEN
Thermoelectric materials, which directly convert heat into electricity based on the Seebeck effects, have long been investigated for use in semiconductor refrigeration or waste heat recovery. Among them, SnSe has attracted significant attention due to its promising performance in both p-type and n-type crystals; in particular, a higher out-of-plane ZT value could be achieved in n-type SnSe due to its 3D charge and 2D phonon transports. In this work, the thermoelectric transport properties of n-type polycrystalline SnSe were investigated with an emphasis on the out-of-plane transport through producing textural microstructure. The textures were fabricated using mechanical alloying and repeated spark plasma sintering (SPS), as a kind of hot pressing, aimed at producing strong anisotropic transports in n-type polycrystalline SnSe as that in crystalline SnSe. Results show that the lowest thermal conductivity of 0.36 Wm-1 K-1 was obtained at 783 K in perpendicular to texture direction. Interestingly, the electrical transport properties are less anisotropic and even nearly isotropic, and the power factors reach 681.3 µWm-1 K-2 at 783 K along both parallel and perpendicular directions. The combination of large isotropic power factor and low anisotropic thermal conductivity leads to a maximum ZT of 1.5 at 783 K. The high performance elucidates the outstanding electrical and thermal transport behaviors in n-type polycrystalline SnSe, and a higher thermoelectric performance can be expected with future optimizing texture in n-type polycrystalline SnSe.
