Enhancement of thermoelectric performance of Cu₂MnSnSe₄ alloys by regulation of lattice strain

Quaternary Cu2MnSnSe4 alloys with low intrinsic thermal conductivity are identified as promising middle-temperature thermoelectric materials. However, zT is depressed by the poor electrical performance. To overcome this issue, here, a series of Cu2.1Mn0.9SnSe4 samples are prepared by ball-milling method which appears as a time-saving technique and lattice strain variation is observed by changing the annealing time (x = 0, 1, 2, 3, 4 days). The vacancy defects concentration of Cu, with lowest vacancy defects formation energy, is changed with the competition between compression and tension-strain state, consistent with the first principles calculations, which optimizes the carrier transport. As a result, about 4 times increment of the carrier mobility is found. Moreover, the lattice strain of several nanometers is observed with TEM analysis, which scatters phonon strongly. A lowest kappa(L) value of 0.57 W m(-1) K-1 at 673 K is obtained for x = 3 sample, which is close to the amorphous limit. The interactive effect of enhanced mobility and strong scattering of phonons, contributing to a record zT similar to 0.48 at 673 K for x = 3 sample. Lattice strain engineering is an effective tactic to simultaneously optimize the electrical and thermal transport.