Enhanced thermoelectric property in superionic conductor Bi-doped Cu1.8S

We report the effect of Bi3+ doping on both electron and phonon transport properties of BixCu1.8-xS (x = 0, 0.004, 0.01, 0.014, 0.02) superionic conductors. An enhanced ZT value in different degrees with x is mainly attributed to an improved electrical conductivity owing to an increased carrier mobility with an undegrated Seebeck coefficient when 0 ≤ x ≤ 0.01, and a reduced thermal conductivity to a low level (0.71-1.00 Wm−1K−1) at x = 0.02 benefiting by the formation of the low-conductive Cu3BiS3 and Cu1.96S second phases. The highest ZT value of 0.61 at 673 K obtained for the Bi0.01Cu1.79S (x = 0.01) sample, which is twice as large as that of the pure Cu1.8S sample. Our result indicates that the introduction of Bi3+ in thermoelectric materials is an effective and convenient strategy to improve ZT by improving the power factor and/or decreasing thermal conductivity.