High symmetry structure and large strain field fluctuation lead enhancement of thermoelectric performance of quaternary alloys by tuning configurational entropy

Quaternary Cu2MnSnSe4 alloys are promising thermoelectric materials due to their earth-abundant nature and environmentally friendly components. Recently, effectiveness of entropy engineering in phonon transport regulation has been demonstrated, while maintaining well electrical properties remains challenging. Here, first principles calculation predicts Fe Co and Zn have weak effect on electronic band edges of Cu2.1Mn0.9SnSe4, so compositions of Cu2.1Mn0.8Fe0.1SnSe4, Cu2.1Mn0.7Fe0.1Co0.1SnSe4, Cu2.1Mn0.6Fe0.1Co0.1Zn0.1SnSe4 are designed with tetragonal structure. Their thermodynamic stabilities are confirmed by analysis of entropy, enthalpy and Gibbs free energy. The increased configurational entropy leads to a well-maintained tetragonal structure with high symmetry, thus obtaining high Seebeck coefficients, which compensate for reduction in electrical con-ductivity. A highest power factor of 732.1 mu Wm- 1 K-2 at 673 K is obtained for Cu2.1Mn0.9SnSe4 sample. Meanwhile, increased configurational entropy also results in large strain field fluctuation and strong anharmo-nicity (gamma = 1.59-1.80) in crystal lattice, which suppress lattice thermal conductivity (Kappa L) together. Consequently, the Cu2.1Mn0.7Fe0.1Co0.1SnSe4 sample obtains the lowest Kappa L of 0.80 W m-1 K-1 at 673 K. Finally, a high Vickers Hardness of 206 Hv and zTmax of 0.40 are achieved in Cu2.1Mn0.8Fe0.1SnSe4. Entropy engineering opens up a channel to optimize the electrical-thermal properties of complex compounds simultaneously.