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In this paper, fine-grained and highly dense n-type Bi 2 Te 2.7 Se 0.3 alloys were prepared via mechanical alloying and a new molding technology named microwave activated hot pressing (MAHP) with relatively low sintering temperature and short holding time. The effects of sintering temperature and holding time on the microstructure and thermoelectric properties of sintered samples were investigated in detail. The results indicated that the sintered alloys could achieve nearly complete densification. Laminated microstructure dominated in the as-MAHPed samples and their size increased gradually with increasing sintering temperature. At the same time, although Seebeck coefficients decreased slightly, their power factors increased obviously due to the drastic decrease of electrical resistivities. And a maximum power factor of 1.81 × 10 − 3 W m − 1 K − 2 was achieved at room temperature for the sample sintered at 693 K for 10 min. A minimum thermal conductivity of 0.61 W m − 1 K − 1 was obtained for the sample sintered at 533 K for 10 min owing to the drastic boundary-phonons scattering effect. A highest ZT value of 0.71 was obtained around 423 K for the Bi 2 Te 2.7 Se 0.3 sample sintered at 613 K without holding time. It confirms that the MAHP technology introduced here can achieve low temperature and rapid sintering process well in preparations of Bi 2 Te 3 -based alloys, and has widely potential applications in other functional materials. [ABSTRACT FROM AUTHOR]

In this work, a new consolidation technique of microwave activated hot pressing (MAHP) was recommended and some fine-grained and highly densified n-type Bi 2 Te 2.85 Se 0.15 compounds were prepared via mechanical alloying combining with MAHP process for the first time. The phase, microstructure and composition of the obtained samples were evaluated by X-ray diffraction, field emission scanning electron microscopy, and energy dispersive X-ray spectroscopy, respectively. The effect of MAHP processing parameters on the microstructure and thermoelectric (TE) properties of the Bi 2 Te 2.85 Se 0.15 compounds was investigated detailedly. The Bi 2 Te 2.85 Se 0.15 powders could be well compacted by the MAHP process and the relative densities of the as-MAHPed bulks were all above 95%. The grain size of the as-MAHPed samples increased gradually with raising sintering temperature and a partially oriented lamellar structure formed at some regions when the sintering temperature was relatively high. The maximum ZT value of 0.57 was obtained for the as-MAHPed Bi 2 Te 2.85 Se 0.15 sample at 373 K, which should be ascribed to the sharply reduced thermal conductivity due to enhanced phonon scattering effect from the contribution of a large number of nanoscale and submicrometer pores dispersed in the matrix. All evidences about electrical and thermal transport properties suggested that the MAHP technique was a potential excellent method to obtain a fine microstructure and improve the TE properties. Different from the conventional hot pressing and microwave pressureless sintering techniques, the MAHP method introduced here was more suitable for practical industrial application due to its cost-saving, energy-saving and high efficiency. [ABSTRACT FROM AUTHOR]

The p -type Bi 0.4 Sb 1.6 Te 3 nanostructured bulk thermoelectric materials were obtained by mechanical alloying combined with a new consolidation technique of microwave activated hot pressing (MAHP). The effect of sintering temperature and holding time on the microstructure and thermoelectric properties of p -type Bi 0.4 Sb 1.6 Te 3 bulks were investigated in detail. Compared with the traditional microwave pressureless sintering, the MAHP technique can be used to produce relatively compact bulks, caused by a uniaxial pressure. Due to the microwave arcing effect, the irregular shape nanograins are formed in situ in the MAHP samples. The coexistence of nano-sized grains and micro-sized grains can promote the effective scattering of phonons of a wide spectrum of wavelength and decrease the lattice thermal conductivity. A minimum lattice thermal conductivity of 0.41 W/(m K) and a maximum dimensionless figure of merit value of 1.13 were obtained for the MAHP sample sintered at 375 °C and 15 min. The MAHP technique introduced in this work can be extended to other ceramics to obtain fine microstructures at low sintering temperatures in a very short period of time. [ABSTRACT FROM AUTHOR]

The p -type Bi 0.4 Sb 1.6 Te 3 nanostructured bulk thermoelectric materials were obtained by mechanical alloying combined with a new consolidation technique of microwave activated hot pressing (MAHP). The effect of sintering temperature and holding time on the microstructure and thermoelectric properties of p -type Bi 0.4 Sb 1.6 Te 3 bulks were investigated in detail. Compared with the traditional microwave pressureless sintering, the MAHP technique can be used to produce relatively compact bulks, caused by a uniaxial pressure. Due to the microwave arcing effect, the irregular shape nanograins are formed in situ in the MAHP samples. The coexistence of nano-sized grains and micro-sized grains can promote the effective scattering of phonons of a wide spectrum of wavelength and decrease the lattice thermal conductivity. A minimum lattice thermal conductivity of 0.41 W/(m K) and a maximum dimensionless figure of merit value of 1.13 were obtained for the MAHP sample sintered at 375 °C and 15 min. The MAHP technique introduced in this work can be extended to other ceramics to obtain fine microstructures at low sintering temperatures in a very short period of time. [ABSTRACT FROM AUTHOR]