Microstructure change and thermal conductivity reduction in p-type Bi–Sb–Te thermoelectric materials using a metal fatty acid as process control agent

[Display omitted] •A metal fatty acid was used as process control agent (PCA) in the ball milling for nanostructured bulk thermoelectric materials.•Particle growth during sintering was suppressed and nanoinclusions were formed in matrix through the simple and scalable process.•The sintered pellet of Bi–Sb–Te powder ball-milled with iron stearate showed enhanced thermoelectric performance at high temperature. Nanostructuring of bulk thermoelectric materials has attracted interest as a promising approach to improve the thermoelectric performance by lowering the thermal conductivity through phonon scattering. In the present study, a metal fatty acid, which is widely used as a precursor that decomposes to form nanoparticles in colloidal chemistry, was used as a process control agent (PCA) in the ball milling for nanostructured bulk thermoelectric materials. A p-type Bi–Sb–Te alloy was ball-milled with different amounts of iron stearate PCA and sintered into bulk pellets. Microstructural analysis clearly showed that particle growth during sintering was suppressed and nanoinclusions were introduced in matrix, which resulted in an increased interface density and low thermal conductivity. As a result of further analysis of the decrease in thermal conductivity, it was found that the bipolar thermal conductivity was reduced, and thus the ZT was improved at high temperature.