Stabilizing Thermoelectric Figure‐of‐Merit of Superionic Conductor Cu2Se through W Nanoinclusions

Cu 2 Se exhibits a high figure‐of‐merit ( ZT ) >1 due to the scattering of phonons by mobile Cu + ions, but migration of the Cu + ions leads to chemical instability at high temperature. It is demonstrated that the incorporation of W in the Cu 2 Se matrix results in peak ZT of 2.1 ( ZT avg = 0.93) at 878 K. After the first thermal cycle, the peak ZT of the composite decreases to stable value of ≈1.5 ( ZT avg = 0.97). The enhanced stability of the nanocomposite along with high ZT avg is attributed to the covering of Cu 2 Se grain boundaries with W that inhibits Cu + migration, reduces Se loss, and improves charge carrier mobility.