Non-equilibrium synthesis and characterization of n-type Bi2Te2.7Se0.3 thermoelectric material prepared by rapid laser melting and solidification

Abstract

Commercial production of thermoelectric (TE) modules features energy-intensive and time-consuming processes. Here, we propose a rapid, facile and low cost fabrication process for n-type single phase Bi2Te2.7Se0.3 that combines self-propagating high-temperature synthesis (SHS) with the laser non-equilibrium 3D printing method based on selective laser melting (SLM). The optimal SLM processing window for high quality single layers has been determined. Results show that the chemical composition of the sample is very sensitive to the laser energy density (EV) due to the selective vaporization of Se and Te. For energy densities EV of less than 33.3 J mm-3, the composition of the SLM-processed samples is relatively stable. However, as EV exceeds 33.3 J mm-3 and increases further, the vaporization rate of Te and Se significantly increases and is much higher than that of Bi. Empirical formulae relating the chemical composition of the resulting materials with the values of EV are obtained and are used to predict the composition of the SLM-processed material. Most importantly, the temperature dependent TE properties of the SLM-fabricated bulk sample result in a maximum ZT value of 0.84 at 400 K, which is comparable to that of the commercially available material. The work has laid a foundation for the future utilization of this technique for the fabrication of Bi2Te3-based thermoelectric modules.