Ultra-fast synthesis of Bi2Te3−xSex based compounds with micro-nano composite structure at room temperature by reactive flash sintering

•Bi2Te3−xSex was synthesized in 2 s at room temperature using Bi, Te and Se powders.•The synthesized Bi2Te3−xSex compound has micro-nano composite structure.•Local Joule heat and ultra-high self-heating rate are inferred for the synthesis.•Mechanism includes Joule heating, melting, reaction, nucleation and grain growth.