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A2: Medium temperature materials

High thermoelectric performance in non-toxic earth-abundant copper sulfide

Ying He1, Tristan Day2, Tiansong Zhang1, Huili Liu1, Xun Shi1,*, Lidong Chen1,* and G. Jeffrey Snyder2,*
1.State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Chinese Academy of Sciences2.Department of Materials Science, California Institute of Technology

Thermoelectric materials and devices can provide a promising possibility to easily convert energy between heat and electricity without moving parts and environmentally benign. Thermoelectric energy conversion efficiency is generally dominated by the dimensionless thermoelectric figure of merit zT. Generally, if the efficiency of thermoelectric devices is to obtain 15%, high zT values averaging at least 1.0 are needed when the temperature difference is 550 K. However, the value of zT in present commercial TE materials is typically less than unity.

By now, many different strategies have been applied to effectively enhance zT, such as micro-structure modification to reduce thermal conductivity and band structure engineering to optimize electrical properties. In particularly, the concept of “phonon-liquid electron-crystal” (PLEC) is first proposed to explain the extraordinarily low thermal conductivity and high thermoelectric performance in the superionic phase of Cu2-xSe. The advantages of liquid-like copper ions for high performance PLEC thermoelectrics include very strong phonon scattering as well as the additional reduction of specific heat due to the suppression of transverse phonon modes. It is found that Cu2-xS is another example of PLEC materials, thus it shows great potential in thermoelectrics. Here, we show very low values of κL below 0.35 Wm-1K-1 and high values of zT about 1.7 in Cu2-xS with slight copper deficiency. Similar to Cu2-xSe, liquid-like copper ions in a rigid sulfide sublattice plays the dominant role for the extraordinarily low κL and high zT values of Cu2-xS. And in Cu2-xS it shows stronger liquid-like phenomen than that in Cu2-xSe correlated to its extraordinarily low transverse acoustic phonon velocity as well as stronger anharmonicity as measured by Grüneisen parameter. In addition, compared to selenium, sulfur has another advantage of being low cost, environmentally benign, low toxicity, and earth-abundant (at least 10,000 times more abundant than selenium in the earth’s crust) correspond wih the industry application requirements of large-scale low cost, environmentally benign, and non-toxic.