Kinetic analysis of the reduction of a ternary system of Bi, Sb and Te oxides by hydrogen for BiSbTe3 synthesis

Highlights: • Synthesis of BiSbTe₃ via reduction of oxides in hydrogen is studied. • Sb₂O₃ was found to oxidize to Sb₂O₄ in a redox reaction with Bi and Te oxides. • The presence of Bi hinders the Te-related self-heating effect. • Presence of oxide particles prevents growth of the synthesized materials' grains. • Homogenous BiSbTe₃ is successfully synthesized through the reduction process. Reduction in a hydrogen atmosphere of Bi₂O₃, Sb₂O₃ and TeO₂ mixes oxides for the synthesis of BiSbTe₃ was analysed. The reduction reactions of Sb₂O₃ and Sb₂O₄ oxides, as well as Bi₂O₃+Sb₂O₃ and Sb₂O₃+3TeO₂ mixtures, were also evaluated. The reduction of Sb₂O₄ is investigated for the first time. The reactions of the mixed oxides systems also were not the subject of research so far despite being used for synthesis of the (Bi,Sb)₂Te₃ material. The study comprised of kinetic analysis of TGA curves performed with non-parametric and isoconversional methods. Insight into powders' structure during the process was taken to identify processes taking place. The results show, that Sb₂O₃ present in the reduced oxidizes to Sb₂O₄. This redox process between Sb oxide and another oxide takes place directly. The self-heating effect caused by elemental tellurium is diminished in the presence of Bi, because Bi-Te phases decrease the content of the elemental Te.