Effects of mechanical alloying process and sintering methods on the microstructure and thermoelectric properties of bulk Bi0.5Sb1.5Te3 alloy

• Pure Bi0.5Sb1.5Te3 alloys can achieve after ball milling for 12 h under certain way.
• Negative Seebeck coefficient appeared in Bi0.5Sb1.5Te3 alloys in certain case.
• Laminated structure is more familiar in HP sample compared with the SPS one.
• HP temperature has important effects on the TE properties of Bi0.5Sb1.5Te3 alloys.

In this study, bulk ternary alloy Bi0.5Sb1.5Te3 was fabricated by mechanical alloying combined with hot pressing (HP) and spark plasma sintering process (SPS), respectively. Differences in microstructure and thermoelectric properties between HP samples and SPS specimens with different ball milling parameters were investigated visually. The results showed that certain improvement in rotate speed of ball milling process can reduce the formation time of Bi0.5Sb1.5Te3 powders from 60 h to 12 h. Mechanical alloying process had an important effect on the Seebeck coefficient of Bi0.5Sb1.5Te3 alloy, negative Seebeck coefficient may even appear due to the deformation induced donor-like effect. The study also discovered that laminated structure was much more familiar in hot pressed Bi0.5Sb1.5Te3 alloy compared with that in the spark plasma sintering samples. The figure of merit of Bi0.5Sb1.5Te3 alloy was enhanced with the increasing hot pressing temperature and reached 0.0027 K−1 around room temperature. Spark plasma sintered samples with 450 rpm + 60 h + 20:1 ball milling parameters have the maximum figure of merit 0.0048 K−1 which is about 1.5 times higher than the maximum TE value of HP samples.