Phase Evolution Mechanism of Cu2Se Compound During Mechanical Milling and Spark Plasma Sintering Process

This article reports the evolution of Cu2Se thermoelectric compound during high-energy ball milling and spark plasma sintering process. The elemental copper (Cu) and selenium (Se) powders with appropriate stoichiometric ratios (Cu 66.66 at.% and Se 33.34 at.%) were milled in the high-energy ball mill at different milling times. The XRD studies of the ball-milled powders show the phase evolution with increasing milling time. The XRD analysis of 1, 5, 10 and 20 h mechanically milled powders is identified as Cu + Se, CuSe + Cu + Se, Cu3Se2 + Cu and beta-Cu2Se phases, respectively. Diffusion-controlled reaction mechanism is proposed for the formation of beta-Cu2Se phase after multiple intermediate phases. DTA studies also report the phase formation of alpha-Cu2Se from the elemental powder and intermediate phases. Spark plasma-sintered sample has shown the formation of alpha-Cu2Se compound irrespective of the milling time and initial phase.