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Boosting High Thermoelectric Performance of Ni-doping Cu1.9S by Significantly Reducing Thermal Conductivity.

At present, copper sulfide materials have been predicted as promising thermoelectric materials due to their inexpensiveness and non-toxicity property. Most research on copper sulfide is focused on Cu2S and Cu1.8S because they are more easily synthesized into single phase, however, the improper electrical conductivity greatly hindered their thermoelectric properties. In this work, a series of high performance Cu1.9-xNixS (x = 0, 0.01, 0.015 and 0.02) bulk samples were fabricated by accurately manipulating the ratio of Cu/S with appropriate Ni doping, and the thermoelectric properties of Ni-doping Cu1.9S were detailedly explored for the first time. It can be found that carrier thermal conductivity and lattice thermal conductivity of Cu1.9-xNixS were effectively reduced via Ni doping, simultaneously, without great influence on power factor. Here, the carrier thermal conductivity (κe) was reduced due to the extreme reduction of Hall carrier concentration. In addition, amounts of nanopores introduced by Ni-doping and complex crystal structure from the phase transition of second phase strengthen the phonon scattering and reduce lattice thermal conductivity (κl) remarkably. As a consequence, the lowest carrier thermal conductivity and lattice thermal conductivity are reached to 0.006 W m-1 K-1 and 1.08 W m-1 K-1 for Cu1.88Ni0.02S at 773 K, and the average ZT is to about 0.39 from 323 K to 773 K (the ZTmax is about 0.9 at 773 K). This work demonstrates that low-cost and easily fabricated Ni-Cu1.9S is a pleasurable candidate for thermoelectric application, in despite of it usually being treated as an ion conductor.