Analytical and Experimental Study of Phonon Transport in Nanostructured Thermoelectric Materials Synthesized from Nigerian Mineral Precursors

Thermoelectric materials capable of converting temperature gradients into electrical power offer attractive possibilities for waste heat recovery in Nigerian industrial settings. Nanostructuring is known to suppress phonon thermal conductivity through boundary scattering while preserving electronic transport properties, thereby enhancing thermoelectric figure of merit. This study analyzes phonon transport in nanostructured bismuth telluride and lead telluride thermoelectric materials synthesized using tellurium mineral precursors obtained from pegmatite mining areas of Nasarawa State, North Central Nigeria. Nanostructured pellets were fabricated by ball milling and spark plasma sintering at grain sizes of 20 nm, 50 nm, 100 nm, and 500 nm. The Seebeck coefficient, electrical conductivity, and thermal conductivity were measured as functions of temperature from 300 K to 700 K. Phonon mean free path spectra were estimated from thermal conductivity data using the Callaway model fitted to measured temperature-dependent thermal conductivity. Results indicate a 58 percent reduction in thermal conductivity at 20 nm grain size relative to bulk material, attributed to grain boundary phonon scattering of mid-frequency phonons in the 1 to 10 THz range. The dimensionless figure of merit ZT reached 1.18 at 480 K for the 20 nm lead telluride samples, exceeding 0.85 for 500 nm grain samples. The study benchmarks results against international nanostructured thermoelectric literature and estimates the performance characteristics of a thermoelectric generator module sized for 100 Watt recovery from industrial exhaust heat streams common in Nigerian cement and glass manufacturing plants. Keywords: thermoelectric, phonon transport, nanostructure, bismuth telluride, Nasarawa State