The origin of ultra-low thermal conductivity of the Bi2Te2S compound and boosting the thermoelectric performance via carrier engineering

Strong Anharmonicity‐Induced Low Thermal Conductivity and High n‐type Mobility in the Topological Insulator Bi1.1Sb0.9Te2S

“…However, in these materials, the bipolar conduction is unavoidable which limits the zT value at high temperature. Bi 8 Se 7 , another member of the above-mentioned homologous family has been recently synthesised which shows a zT of � 0.5 at 573 K. [41] Tetradymite mineral, Bi 2 Te 2 S is a 3D topological insulator which lies in the ternary phase diagram of Bi 2 Te 3 -Bi 2 S 3 system [42][43][44] and has a similar crystal structure like Bi 2 Te 3 (space group: R3 ̄m).The only difference is that the Te layer, sandwiched between the two Bi layers, is replaced by S. [38,42,45] However, the actual stoichiometry of the compound is debatable. According to Linus Pauling, the structure with 2 : 2 : 1 stoichiometry is not stable because tremendous amount of strain is developed when Te layer is replaced by S due to large size difference between S 2À (184 pm) and Te 2À (221 pm).…”

Zn-Induced Defect Complexity for the High Thermoelectric Performance of n-Type PbTe Compounds

“…It is also worth noting that the improvement in the average ZT of the material over the working temperature range is more important than that in the peak ZT value at a certain temperature concerning the operation efficiency of the thermoelectric device in practice. − To date, tremendous investigations have demonstrated that the effective approaches to maximize the ZT value can be categorized by boosting electrical transport properties and/or decreasing thermal conductivity. The methods to boost the power factor include appropriate levels of doping to optimize carrier concentration, the introduction of unique defect structures, electronic band structure engineering, etc. − Meanwhile, nanostructuring, the formation of solid solution, and all-length-scale hierarchical architectures have pronounced great effectiveness in lowering the thermal conductivity. − So far, considerable efforts based on the above strategies have been made toward achieving high thermoelectric performance in the existing thermoelectric materials, including (Bi, Sb) 2 Te 3 alloys, − PbTe-based compounds, − and SnTe-based materials. − …”

Removing the Oxygen-Induced Donor-like Effect for High Thermoelectric Performance in n-Type Bi2Te3-Based Compounds

“…To improve the thermoelectric performance and mechanical properties of Bi 2 Te 3 -based materials, most research was focused on polycrystallizing Bi 2 Te 3 -based compounds by the powder metallurgy method. − Nanostructure engineering was adopted to intensify grain boundary phonon scattering and reduce lattice thermal conductivity; meanwhile, excellent electrical properties were maintained, thus making ZT values greatly ascend. − In addition, the grain size refinement and nanostructures also improve the mechanical properties. Compared with zone melting samples, the mechanical properties of SPS sintered samples can be improved by 6–7 times. ,,,− A number of investigations have proven that nanostructuring is undoubtedly successful for p-type Bi 2 Te 3 -based compounds. − However, for n-type Bi 2 Te 3 -based compounds, upon the refinement of grain sizes, the grain boundaries scattering on electrons as well as the weakened orientation of grains in polycrystalline samples lead to a sharp decrease in carrier mobility and significantly degraded electrical transport properties. ,, Besides, the donor-like effect generated in the fracturing process of ingots makes the carrier concentration of the materials increase dramatically, largely deviating from their optimum carrier concentration range.…”