Precursor Effects and Formation Mechanism of Polyol-Synthesized Thermoelectric Bi2Te3

Abstract

Polyol synthesis offers a controllable and scalable approach for producing high-performance thermoelectric materials such as bismuth telluride (Bi2Te3), providing more control over crystal growth and microstructure compared to conventional solid-state methods. The chemical nature of the selected precursors can strongly influence the reaction pathways, phase evolution, and resulting material properties. In this work, two polyol synthesis routes using Bi2O3 and Bi(NO3)3·5H2O as bismuth precursors were systematically investigated to evaluate their influence on the structural evolution and thermoelectric performance of Bi2Te3. Comparative characterization and transport measurements reveal clear precursor-dependent variations in microstructure and anisotropic charge transport. Despite being undoped, both materials exhibit strong thermoelectric performance with the nitrate-derived sample achieving a peak figure of merit of zT = 1.27 at 432 K, and the oxide-derived material reaching zT = 1.10 at 333 K. Moreover, analysis of the nitrate route revealed the formation of a previously unreported bismuth complex, Bi3(C2H4O2)4NO3. Overall, these findings advance the mechanistic understanding of Bi2Te3 formation in polyol synthesis and highlight the importance of precursor selection as a key parameter for tailoring microstructure and optimizing thermoelectric performance.