Hardening of Bi–Te based alloys by dispersing B4C nanoparticles

Abstract Thermoelectric devices have attracted a great attention for renewable energy harvesters and solid-state coolers. For practical applications, the mechanical properties of thermoelectric materials become critical for the device reliability, a persistent performance with a long time and high operation cycles. Bi–Te based single-crystals, mostly used in commercial thermoelectric devices, are intrinsically brittle with weak van der Waals bonding, often leading to device failures such as crack and debonding during fabrication and operation. Thus, it is highly desirable to enhance the mechanical property of Bi–Te based alloys as well as the thermoelectric property. Here, we investigate the effect of B 4 C nanoparticles (less than 0.5 wt%) dispersed in p -type Bi 0.4 Sb 1.6 Te 3 matrix on the mechanical properties. X-ray diffraction (XRD) result confirms that B 4 C-dispersed Bi 0.4 Sb 1.6 Te 3 has a single phase. We observe that the grain size of Bi 0.4 Sb 1.6 Te 3 becomes decreased with the B 4 C nanoparticle concentration by electron backscatter diffraction (EBSD) technique. Hardness, Young’s modulus, and flexural strength of B 4 C-dispersed Bi 0.4 Sb 1.6 Te 3 are enhanced, compared to the B 4 C-free Bi 0.4 Sb 1.6 Te 3 polycrystals. On the other hand, the thermoelectric figure-of-merit of B 4 C-dispersed Bi 0.4 Sb 1.6 Te 3 is almost identical to that of the pure Bi 0.4 Sb 1.6 Te 3 . Such enhancements of the mechanical properties of the B 4 C-dispersed Bi 0.4 Sb 1.6 Te 3 are attributed to the grain boundary hardening and second-phase hardening. Beyond thermoelectric materials, our result implies that the grain refinement by nanoparticle dispersion is a simple and promising way to strengthen the mechanical properties of other brittle materials with layered structure.