Empirical Investigation of the Seebeck Coefficient and Thermoelectric Figure of Merit of Bismuth Telluride Composites for Waste Heat Recovery Applications

Background: Bismuth telluride-based composites are leading thermoelectric materials for low-grade waste heat recovery, but composition optimisation for operation in the temperature range typical of Nigerian industrial exhaust streams remains insufficiently characterised. Aim: This study empirically investigated the Seebeck coefficient, electrical resistivity, thermal conductivity, and thermoelectric figure of merit of Bi2Te3 and Bi2Te3-Se composite samples synthesised by solid-state reaction. Methods: Samples with varying selenium substitution fractions from 0 to 30 atomic percent were synthesised by ball milling and hot pressing. Thermoelectric properties were measured from 300 to 500 K using a ZEM-3 characterisation system and a laser flash diffusivity analyser. Hall effect measurements provided carrier concentration data. Results: Maximum ZT of 1.31 was achieved at 373 K for the 15 at.% Se-substituted composite, an improvement of 34% over binary Bi2Te3. Seebeck coefficient peaked at 242 microvolts per Kelvin. Phonon scattering at grain boundaries was identified as the primary thermal conductivity reduction mechanism. Conclusion: Selenium-substituted Bi2Te3 composites offer meaningful ZT enhancement for waste heat recovery in the 300 to 450 K range relevant to Nigerian industrial applications. Further optimisation of grain boundary engineering is recommended. Keywords: thermoelectric, Seebeck coefficient, bismuth telluride, waste heat recovery, figure of merit.