Thermoelectric Behaviors of Bi0.3Sb1.7Te3.0 with Excess or Deficiency of Tellurium Prepared by Mechanical Alloying Followed by Hot Pressing

Bi0.3Sb1.7Te3.0+x thermoelectric materials with a deficiency or excess of doped tellurium (x from -0.025 to +0.2) were prepared by mechanical alloying followed by hot pressing (MA-HP). The MA-HP sintered disks were dense and finely grained. X-ray diffraction (XRD) patterns showed that materials with x < 0.2 consisted of a single-phase Bi2Te3-Sb2Te3 solid solution. XRD and scanning electron microscopy showed that tellurium precipitation only occurred in the MA-HP sintered disk with x = 0.2. The thermoelectric properties of MA-HP sintered disks of Bi0.3Sb1.7Te3.0+x with a tellurium-deficient region differed from those of disks with an excess-tellurium region. Tellurium deficiency, i.e., x < 0.05, was caused by dopant evaporation. Excess tellurium acted as a dopant for x > 0.075. The MA-HP sintered disk of Bi0.3Sb1.7Te3.1, i.e., x = 0.1, had the maximum dimensionless figure of merit, ZT = 1.11, at room temperature. These results indicate that the thermoelectric properties of Bi0.3Sb1.7Te3.0 thermoelectric materials with excess tellurium were better than those of tellurium-deficient ones.