Phase purification for enhanced room-temperature ductility in complex bulk thermoelectric materials

Flexible thermoelectric (FTE) technology offers promise for self-powering flexible electronics based on the materials with both high thermoelectric (TE) performance and exceptional flexibility. Recently, ductile inorganic semiconductors such as AgCu(Se,S,Te) exhibit remarkable room-temperature ductility and high TE performance, but their compositional and structural complexity often lead to detrimental phase complexity and sometime secondary phases, which greatly hinder the fundamental study and real applications. In this work, we systematically investigate the critical role of phase purity in enhancing both ductility and TE properties in AgCu(Se,S,Te) materials. By precisely controlling the quenching temperature during synthesis process, the secondary phases with different microstructure can be controllably created inside the matrix of AgCuSe_0.22S_0.08Te_0.7. Notably, quenching at 923 K produces a monophasic microstructure that exhibits exceptional room-temperature ductility (over 75% compressive strain, over 20% bending strain, and 15% tensile strain) while retaining excellent TE performance ( zT = 0.3@300 K, 0.45@340 K). Our results establish that targeted synthesis enabling phase purification is an effective strategy to concurrently optimize mechanical properties and TE performance in ductile inorganic semiconductors, providing a crucial roadmap for developing high-performance FTEs.