Sintering temperature effect on thermoelectric properties and microstructure of the grained Bi1.9Gd0.1Te3 compound

Elemental composition, crystal and grain structures, specific electrical resistivity, thermopower, thermal conductivity, and thermoelectric figure-of-merit of grained Bi1.9Gd0.1Te3 compounds sintered at TS = 690, 720, 735, 750, 780 and 810 K have been studied. Strong TS – effect on the grain structure was found. Fine-grained samples with average grain size of ˜500 nm were prepared at TS = 690, 720 and 735 K, whereas coarse-grained samples with average grain size above 1100 nm were sintered at TS = 750, 780 and 810 K. Evaporation of Te takes place at high temperatures, which results in forming of anti-site defects of Bi in Te-sites. Electrical and thermal properties of the fine-grained and coarse-grained samples happened to be rather different. The highest value of the thermoelectric figure-of-merit equal to ˜ 0.55 was observed for the sample sintered at TS = 750 K. This temperature corresponds to transition from the fine-grained to coarse-grained samples.