Vacancy-Based Defect Regulation for High Thermoelectric Performance in Ge₉Sb₂Te_12–x Compounds

Abstract

Defect engineering is the core strategy for improving thermoelectric properties. Herein, cation doping along with modulation of cation vacancy has been developed in GeTebased materials as an effective method to induce vacancy-based defects to boost their thermoelectric performance. A series of ternary compounds of Ge 9 Sb 2 Te 12−x (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15) was prepared by vacuum-melting and annealing combined with the spark plasma sintering (SPS) process. The role of Sb doping and cation vacancy on thermoelectric properties was systematically investigated. It is found that alloying Sb 2 Te 3 into GeTe increases the concentration of cation vacancies, which is corroborated by both positron annihilation measurements and theoretical calculations. The vacancies, stacking faults, and planar defect interactions determine the thermoelectric transport properties. Adjusting the deficiency of Te effectively tunes the concentration of cation vacancies and dopant defects in the structure. In turn, this tunes the carrier concentration close to its optimum. A high power factor of 32.6 μW cm −1 K −2 is realized for Ge 9 Sb 2 Te 11.91 at 725 K. Moreover, large strains induced by the defect structures, including Sb dopant, vacancy, staking faults, as well as planar defects intensify phonon scattering, leading to a significant decrease in the thermal conductivity from 7.6 W m −1 K −1 for pristine GeTe to 1.18 W m −1 K −1 for Ge 9 Sb 2 Te 11.85 at room temperature. All of the above contribute to a high ZT value of 2.1 achieved for the Ge 9 Sb 2 Te 11.91 sample at 775 K.

Interplay Between Electronic States and Structural Stability in Cation-Deficient VCoSb, NbCoSb, and TaCoSb Half-Heuslers

“…[7][8][9][10] In thermoelectric materials, the presence of vacancy defects can help to tune the power factor or/and the lattice thermal conductivity to deliver a higher figure-of-merit (ZT). Thus, one finds reports of vacancies assisting the desired reduction of the lattice thermal conductivity in CuGaTe 2 , 11 while in SnTe-In 2 Te 3 , 12 Ge 9 Sb 2 Te 12 , 13 and -Zn 4 Sb 3 , 10 the presence of vacancies simultaneously improves the electrical properties and reduces the lattice thermal conductivity. In these improved thermoelectric examples, as in most cases in the field of thermoelectricity, the target was materials with good semiconducting behavior.…”

Achieving Ultralow Lattice Thermal Conductivity and High Thermoelectric Performance in GeTe Alloys via Introducing Cu2Te Nanocrystals and Resonant Level Doping

“…Thus, many previous studies focus on optimizing the carrier concentration for advancing thermoelectric GeTe. − Electron donor doping of Sb/Bi has been adopted to suppress the intrinsically high carrier concentration . Additionally, Ge self-compensation or increasing formation energy of Ge vacancy was used to decrease the carrier concentration for improving the power factor. ,, The Seebeck coefficient of GeTe can be enhanced by creating resonant states near the Fermi level, ,, subvalence band convergence, ,, band alignment, , and slight symmetry reduction . Alternatively, solid solution point defects, nano precipitates, and sandwich-like stacking faults were demonstrated to lower the lattice thermal conductivity for enhancing the ZT of GeTe.…”

Regulating Te Vacancies through Dopant Balancing via Excess Ag Enables Rebounding Power Factor and High Thermoelectric Performance in p‐Type PbTe

“…[ 15 ] Few studies have been conducted to improve the TE properties by controlling the vacancy concentration near room temperature. [ 16 ] However, it is challenging to regulate vacancy formation at high temperatures, as it is thermodynamically stable. [ 14 , 17 ] Therefore, a novel design rule is required to suppress the spontaneous formation of vacancies.…”