Enhanced thermoelectric property in superionic conductor Bi-doped Cu_1.8S

We report the effect of Bi³⁺ doping on both electron and phonon transport properties of Bi_xCu_1.8-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 Cu_1.96S second phases. The highest ZT value of 0.61 at 673 K obtained for the Bi_0.01Cu_1.79S (x = 0.01) sample, which is twice as large as that of the pure Cu_1.8S 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.