Effect of microstructure and composition on thermoelectric properties of Te-rich Sb2Te3

The effect of excess tellurium, including tellurium content and its dispersion state, on the thermoelectric properties of Te-rich Sb₂Te₃ was studied. The Sb₂Te₃ boules with 60~90 mass%Te were grown by Bridgman-Stockbarger method and identified by means of X-ray diffraction (XRD). The microstructure and Sb-distribution in the boules were observed by SEM and EPMA. The boules containing from 60 to 61.9 mass%Te were a single phase of Sb₂Te₃, while the boules containing more than 62 mass%Te consisted of Sb₂Te₃ phase and eutectic phase with Te-Sb₂Te₃ lamella structure, and the boule containing 90.7 mass%Te was only Te-Sb₂Te₃ lamella structure. Hall coefficient and electrical resistivity ρ were measured over the temperature range from 100 to 500 K. Seebeck coefficient σ was measured over the temperature range from 300 to 500 K. Hall concentration of a boule with 60.7 mass% was of 1.09×10²⁶/m³ at room temperature. Hall concentration decreased with increasing Te contents. The boule containing 70.0 mass%Te showed a largest α ²/ρ value of 7.05×10^-3 W/(K²m) at 350 K