Synergistic enhancements of strength-ductility of α-Cu2Se via interlayer reinforcement

Abstract

Robust mechanical performance is essential for thermoelectric (TE) material applications. Cu₂Se, a promising TE material, exhibits intrinsic room-temperature brittleness. In this work, the brittleness of α-Cu₂Se is attributed to weak interlayer Cu-Se bonding through density functional theory (DFT). To reinforce interlayer, weak Cu-Se bonds are substituted by Cu-S or Cu-Te bonds via doping. S-doping elevates cleavage energy and suppresses interlayer cleavages. Moreover, both dopants increase slip energy barriers, raising slip activation stress. Experimentally, compression tests on Cu₂Se, Cu₂Se_1-xS_x and Cu₂Se_1-xTe_x (x = 0-0.1) revealed that, Cu₂Se_0.9S_0.1 achieved simultaneously increases in strength (by 53%) and fracture strain (by 123%). Scanning electron microscope further confirmed the suppression of S-doping on high-density interlayer cleavages. This work provides an interlayer strengthening strategy for simultaneously improving ductility and strength of layered Cu₂Se.