Complex alloying effect on thermoelectric transport properties of Cu₂Ge(Se_1-xTe_x)₃

To enhance the thermoelectric performance of Cu₂GeSe₃, a series of Te-alloyed samples Cu₂Ge(Se_1-xTe_x)₃ are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x=0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution, together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a zT of 0.55@750 K is obtained for the sample with x=0.3, about 62% higher than that for the pristine sample.