Promising thermoelectric materials of Cu3VX4 (X=S, Se, Te): A Cu-V-X framework plus void tunnels

Skutterudites and half-Heusler compounds are well-studied promising thermoelectric (TE) materials due to favorable electrical properties. However, their intrinsic lattice thermal conductivities are so high that various methodologies have been developed to decrease them. Based on our first-principles phonon calculations, we find that thermodynamically stable Cu3VX4 (X=S, Se, Te) compounds exhibit good thermoelectric properties due to their special crystal structure (a Cu-V-X framework plus large void tunnels). The mechanically stable framework is the favorite pathway for the carrier conduction, which induces high electrical conductivity and power factor (comparative to those of filled-skutterudites and half-Heusler systems). Moreover, the void tunnels in the crystal structure result in unsaturated coordinations at the X sites and corresponding lone-pair electrons, which lower the lattice thermal conductivity. The calculated intrinsic lattice thermal conductivity of Cu3VX4 is much lower than those of the well-studied skutterudites and half-Heusler compounds. Thus, the maximum ZT values approach 1.6 (at 900K, 1020cm−3) and 1.2 (at 1000K, 1021cm−3) for the p- and n-type Cu3VTe4 compounds, respectively. Our work provides not only distinctive high-performance TE materials (Cu3VX4), but also a guideline for future promising thermoelectric discoveries.