A study of the kinetics of bismuth telluride synthesis by an oxide reduction method

Abstract The kinetics of a reduction of bismuth and tellurium oxides in a hydrogen atmosphere, leading to the formation of thermoelectric bismuth telluride is investigated. The evaluation of the reaction kinetics was based on a thermogravimetric analysis performed in non-isothermal conditions. A non-parametric analysis method and the Friedman method were used for the evaluation of the data. Additionally, for a better understanding of the process, reactions of the reduction of Bi2O3, TeO2 as well as Bi2Te2O7 and Bi2Te4O11, which are formed as intermediate products, were investigated. The activation energies calculated for the reactions were between 56 kJ/mol in the case of the Bi2Te2O7 reduction and 100 kJ/mol for the reduction of mixed oxides. No correlation between the activation energy and the Bi:Te ratio in the reduced material was found. The calculated conversion functions also differed between the investigated reactions. A self-heating process was found for TeO2 and Bi2Te4O11 reduction reactions. In the case of the tellurium oxide, it was assigned to the melting of Te nanoparticles. These effects were also found to enhance the synthesis of Bi2Te3 by the reduction of mixed bismuth and tellurium oxides. The resulting thermoelectric material was found to be completely reduced, with no traces of oxygen inthe XPS spectrum. EDX mapping of the cross-section of material’s grains revealed a homogenous distribution of elements in the final product.