Ultrafine Interwoven Dendritic Cu₂Se/CuFeSe₂ Composites with Enhanced Thermoelectric Performance

As an effort to develop high-performance and stable copper chalcogenide thermoelectrics, several (1 – x)Cu2Se/(x)CuFeSe2 composites were successfully synthesized via a one-step solid-state transformation of a CuSe2 template. Uniform ultrafine dendritic structures consisting of interweaving Cu2Se and CuFeSe2 nanofibers were observed in samples with low Fe content (0.05 ≤ x ≤ 0.1). Increasing the Fe content to x = 0.5 led to phase segregation into the Cu2Se-rich region with embedded CuFeSe2 fine structures interwoven with the CuFeSe2-rich region containing Cu2Se nanofibers. The formation of such an entwined dendritic structure is believed to arise from the temperature-dependent solubility of CuFeSe2 in the Cu2Se matrix. The dynamic dissolution of CuFeSe2 into the Cu2Se at high temperatures leads to temperature-dependent doping of the Cu2Se matrix, enabling drastic enhancements of thermoelectric power factor at high temperatures. Such a strategy is expected to be a powerful tool for property modulation in thermoelectric materials.