Harnessing anion vacancy for tailored thermal transport in Sb2Te3 thermoelectrics

Strategically manipulating defect dynamics in a crystalline solid can modulate lattice vibrations, thereby reducing thermal transport through the lattice and making it suitable for diverse applications such as thermoelectrics. However, purposefully increasing the concentration of defects often leaves an adverse effect on the charge-carrier mobility, which drags down its thermoelectric performance. Here, to address this challenge, we have devised a strategy to suppress the lattice thermal conductivity (kappa L) without hampering the charge-carrier transport to achieve an improved thermoelectric figure of merit, z, in Sb2Te3 by creating anion vacancy. Successful creation of Te vacancy is confirmed by synchrotron x-ray diffraction study and extended x-ray absorption fine-structure measurements. With increasing Te vacancy, a substantial decrease in kappa L is observed with the lowest kappa L similar to 0.75 Wm-1K-1 obtained at room temperature for 10 mol. % Te-vacant sample. Our attempt to fit the kappa L data by the Debye-Callaway model divulges that anion vacancy makes the lattice more anharmonic and introduces significant point defects which suppress the conduction of phonons. The density of vacancy-induced dislocations in tellurium-vacant samples increases, leading to heightened scattering of heat-carrying phonons. Despite a noteworthy decrease in kappa L, the charge-carrier mobility remains nearly unaffected, resulting in an enhanced thermoelectric performance in the Te-deficient Sb2Te3 sample.