Enhanced zT due to non-stoichiometric induced defects for bismuth telluride thermoelectric materials

Thermoelectric materials have potential applications in energy conversion and waste heat recovery. Thermoelectric materials with non-stoichiometric composition may exhibit improved thermoelectric properties compared to the stoichiometric composition material. Bi2Te3 is one of the best-known thermoelectric materials having optimum performance near room temperature. In the present study, non-stoichiometric bismuth telluride (Bi2 ⠁x Te3), x = (0, 0.01, 0.02, 0.03), was synthesized using the co-precipitate method to create imperfections and strains in the crystal structure of the material. The crystal structure of the synthesized bismuth telluride revealed significant changes in the c direction when examined using X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed the formation of micro-particles. Energy dispersive spectroscopy (EDX) also confirmed the nonstoichiometric elemental composition of Bi and Te rich bismuth telluride. Thermogravimetric analysis (TGA) was performed in a non-inert environment, and an oxidation temperature of 685 K was recorded in nonstoichiometric samples. The post-oxidation of stoichiometric and non-stoichiometric Bi Rich and Te Rich bismuth tellurides was also confirmed by XRD and TGA comparison. The thermal conductivity was reduced by the imperfections and defects for all non-stoichiometric compositions, and a zT value of 0.54 at 420 K was obtained in the Tellurium Rich bismuth telluride, which is about a 12% improvement compared to the pure sample.