Microwave activated hot pressing: A new consolidation technique and its application to fine crystal bismuth telluride based compounds

In this work, a new consolidation technique of microwave activated hot pressing (MAHP) was recommended and some fine-grained and highly densified n-type Bi2Te2.85Se0.15 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 Bi2Te2.85Se0.15 compounds was investigated detailedly. The Bi2Te2.85Se0.15 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 Bi2Te2.85Se0.15 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.