Improved electrical transport properties and optimized thermoelectric figure of merit in lithium-doped copper sulfides

摘要

Copper sulfide Cu_2S is a p-type semiconducting compound that has attracted great attentions in the thermoelec tric(TE) community most recently. Considering the intrinsic ultralow lattice thermal conductivity, the enhancement of TE performance in Cu_2S should be achieved through improving its electrical transport properties. To achieve this goal, lithium element was doped into Cu_2S in this study. A series of Cu_(2-x)Li_xS samples with different Li contents(x=0.0.005,0.010,0.050,and0.100) was synthesized by the melting-annealing method.When x ≤ 0.05, the Cu_(2-x)Li_xS samples are stable and pure phases, having the same monoclinic structure with the pristine Cu_2S at room temperature. The electrical conductivities in the Cu_(2-x)Li_xS samples are greatly improved with the Li-doping content increasing due to the enhanced carrier concentrations. Meanwhile, doping Li into Cu_2S increases the ionic activation energy and lessens the influence of mobile Cu ions on the heat-carrying phonons.Thus, the thermal conductivities of the Li-doped Cu_2S samples increase. A maximal figure of merit(zT) of 0.84 at900 K is obtained in Cu_(1.99)Li_(0.01)S, about 133% improvement as compared with that in Cu_2S matrix.