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• Fabricated porous structure in p-type Cu 0.07 Bi 0.5 Sb 1.5 Te 3 compounds by assisting PVA as pore former and studied TE properties. • Lattice thermal conductivity effectively decreased by ~ 38% due to intensified phonon scattering at microscale pores. • The maximum ZT of 1.342 at 400 K and η max of ~ 9.4% at ∆T = 200 K was obtained for the sample with porosity of 10.58%. • The hardness and compressive strength of porous bulks show significantly higher than commercial zone melting materials. [Display omitted] In the background of enhancing thermoelectric (TE) figure of merit of solid-state materials, the introduction of porous structure can significantly decrease lattice thermal conductivity by intensifying phonon scattering at the inhomogeneous microscale pores. Herein, we developed a porous structure in Cu 0.07 Bi 0.5 Sb 1.5 Te 3 compounds by utilizing PVA as the pore former, and systematically studied its effect on thermoelectric properties. The results revealed that the reduction in thermal conductivity (~28%) was greater than the decrease in electrical conductivity (~17%) with increasing porosity, indicating long-wavelength phonon scattering was enhanced at micro-scale pores. Consequently, a peak zT of 1.342 at 400 K, and a zT avg of 1.254 in the temperature range of 300–500 K and an η max of ~9.4% at ΔT = 200 K were achieved in the porous sample (10.58%), which all are higher than that of dense sample. The hardness and compressive strength of the porous samples were significantly higher than commercial zone melting ingots. The proposed methodology is a cost-effective and efficient way of producing high-performance TE devices with good mechanical stability for real life practical applications. [ABSTRACT FROM AUTHOR]

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi 0.5 Sb 1.5 Te 3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials. [Display omitted] • Novel fabrication of hierarchical structured material with successive arrangement of two different microstructures. • Successful consolidation of well-bonded hierarchical material and confirming by simulating results from COMSOL software. • Highest power factor of 3.8 * 10−3 W/m-K2 obtained by transportation of charge carriers through two different energy levels. • Hierarchical structured sample show highest figure of merit of 1.25 at 400 K which is highest among all reported samples. [ABSTRACT FROM AUTHOR]

Decoupling the Seebeck coefficient, electrical and thermal conductivity has been a great challenge in efforts to obtain thermoelectric materials with a high figure of merit (ZT) for power generation and cooling applications. In this work, p-type Bi 0.5 Sb 1.5 Te 3 samples were fabricated by combining gas atomization and spark plasma sintering. Heat-treatment and subsequent consolidation during SPS stimulated the recrystallization of grains and reduced texture, contributing to reduced carrier scattering. This enhanced carrier mobility by 29%. The recrystallization also induces a hierarchy of fine and coarse crystal grains with random orientations. This mixed microstructure contributed to the simultaneous enhancement of the Seebeck coefficient and electrical conductivity, while reducing lattice thermal conductivity, due to effective phonon scattering by the fine grains and Sb 2 O 3 nanoparticles. The significant improvement in power factor and relatively low κ L resulted in a peak ZT of 1.1 at 350 K for the 470 °C treated sample. This was about 47% higher than the initial sample (ZT = 0.75 at 350 K). The average ZT for all the heat treated samples reached over unity in the range of 300–500 K. This work suggests that the spark plasma heat treatment and consolidation processes enable the recrystallization, allowing the thermoelectric properties to be decoupled, enhancing ZT. Image 1 • The hierarchical structures were formed in Bi 0.5 Sb 1.5 Te 3 alloys via recrystallization. • Decoupled the electrical and thermal properties by forming the hierarchical structures. • Heat-treatment and subsequent consolidation during SPS stimulated the recrystallization of grains and reduced texture. • ZT enhanced by 47% for recrystallized samples than the initial samples. [ABSTRACT FROM AUTHOR]

• Produced large-scale (3 Kg/batch) of 75%Sb 2 Te 3 -25%Bi 2 Te 3 powder by gas atomization. • The hot isostatic pressed bulk displays random distribution of grains. • Higher electrical conductivity achieved for 450 °C sample due to high mobility. • Peak ZT of 1.15 obtained for HIPed at 450 °C sample due to high conductivity values. For economic viability of thermoelectric modules, issues of scalability and sturdiness to drive down production and manufacturing cost must be adequately addressed. In this study, we report a large-scale production of 3 Kg/batch of 75%Sb 2 Te 3 -25%Bi 2 Te 3 powder by gas atomization. The as-produced large-scale atomized powder was subsequently sintered by hot isostatic pressing (HIP) at two different temperatures. The microstructure of the HIPed fracture surface reveals a transgranular mode of fracture in the basal plane of the grains perpendicular to the contact surface. The texture analysis showed that grains were randomly distributed and indicating no preferred alignment in any direction. The sample HIPed at 450 °C shows the highest electrical conductivity of 1350 Ω−1 cm−1 at room temperature due to their high carrier mobility. The highest ZT of 1.15 at 375 K was observed for the sample HIPed at 450 °C owing to their high electrical conductivity, and reasonable low thermal conductivity. [ABSTRACT FROM AUTHOR]