Multiple nanostructures in high performance Cu2S0.5Te0.5 thermoelectric materials

Cu2(S,Te) solid solution material has shown excellent thermoelectric performance with a maximum zT value up to 2.1. Previous work has observed specific mosaic nanocrystals in this solid solution which is considered to be responsible for its ultra-low thermal conductivity. In the present study, we performed in-depth microstructural examinations by transmission electron microscopy and revealed additional multiform nanostructures in Cu2S0.5Te0.5 solid solution. Apart from widely existed mosaic nanocrystals, nano-domains of ordered structure, nanoscale periodic antiphase domains, stacking faults and polytype have been observed. Formation of such abundant nanoscale substructures could be related to the large mismatch in atomic size between S and Te solute elements. These nanostructures are all coherently embedded in the matrix lattice. Thereafter, continuous carrier transportation is still guaranteed while in the meantime phonon scattering is enhanced by such high density of structural imperfection. Thus, solid solution strategy in Cu2S0.5Te0.5 matches well with the phonon-glass electron-crystal concept for high performance thermoelectric materials.