Ultra-fast synthesis of Bi₂Te_3−xSe_x based compounds with micro-nano composite structure at room temperature by reactive flash sintering

The synthesis of Bi₂Te_3−xSe_x (x = 0 and 0.3) compounds in a few seconds at room temperature was realized by reactive flash sintering method using Bi, Te and Se raw powders. The phase transition and microstructure evolution during flash sintering were systematically studied relating to the duration time, power density and sample temperature. The synthesized Bi₂Te_3−xSe_x compounds have micro-nano composite structure, which are composed of 5–10 μm lamellar crystal and 10–20 nm nanograin. It is suggested that the instantaneously generated local Joule heat throughout the sample and the resulted ultra-high self-heating rate approaching tens of thousands K/min are responsible for the synthesis of highly crystalline Bi₂Te_3−xSe_x. The synthesis mechanism is proposed, including Joule heating, melting, chemical reaction, nucleation and grain growth. This highly efficient and economic synthesis method of Bi₂Te_3−xSe_x compounds with micro-nano composite structure has great potential for application in the field of thermoelectric industry.