Enhanced Thermoelectric Properties of p-type Bi0.5Sb1.5Te3 Thermoelectric Materials by Mechanical Alloying and Spark Plasma Sintering

In this research, the microstructure and transport properties of p-type Bi0.5Sb1.5Te3 thermoelectric materials were investigated as a function of milling time. The p-type Bi0.5Sb1.5Te3 alloys were fabricated by mechanical alloying of elemental chunks of bismuth, antimony, and tellurium. This was followed by plasma spark sintering at 673 K. The micro-Vickers hardness (98.7 Hv) was considerably improved in the 90-min sample due to the presence of fine grains in the matrix that prevented crack propagation via grain-boundary hardening. The lowest lattice thermal conductivity (0.63 W/mK) was obtained for the 90-min sample, a value slightly lower than the minimum total thermal conductivity (0.872 +/- 0.5 W/mK at 300 K) due to strong scattering of phonons and carriers owing to the completely randomness of the distribution of the fine-grain structure in the bulk samples. The maximum figure-of-merit (ZT = 0.98 +/- 0.5 at 300 K) was obtained for the 90-min sample due to its superior power factor values.