The effect of graphene on the activation energy of grain growth for the nanocrystalline thermoelectric n‑type Bi2Te2.7Se0.3

Abstract

Even though bismuth telluride is frequently produced by mechanical alloying for thermoelectric materials, no data has been published addressing the thermal behavior and activation energy of the milled n-type Bi2Te2.7Se0.3 powders. This paper studies the activation energy of grain growth for the nanocrystalline n-type Bi2Te2.7Se0.3 and two graphene-Bi2Te2.7Se0.3 composites with diferent graphene concentrations (0.05 and 0.5 wt.%). Grain size and structural analyses of these samples have been carried out using X-ray difraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the three samples is investigated by incorporating diferential scanning calorimetry data with the Kissinger model. The activation energy of the pristine Bi2Te2.7Se0.3 alloy is found to be 268 kJ/mol. For the composite samples, a lower graphene weight percentage (0.05 wt.%) increased the activation energy to 270 kJ/mol. In contrast, higher amounts of graphene (0.5 wt.%) reduced the activation energy signifcantly to 254 kJ/mol. The observed efect is found to be directly related to graphene’s exfoliation in the bismuth telluride matrix. These results ofer a better understanding of the thermal behavior of the nanocrystalline pristine n-type Bi2Te2.7Se0.3 and the infuence of graphene nanofller on the thermal stability of the bismuth telluride nanocomposites.