From thermoelectric bulk to nanomaterials: Current progress for Bi₂Te₃and CoSb₃

Bi₂Te₃and CoSb₃based nanomaterials were synthesized and their thermoelectric, structural, and vibrational properties analyzed to assess and reduceZT‐limiting mechanisms. The same preparation and/or characterization methods were applied in the different materials systems. Single‐crystalline, ternary p‐type Bi₁₅Sb₂₉Te₅₆, and n‐type Bi₃₈Te₅₅Se₇nanowires with power factors comparable to nanostructured bulk materials were prepared by potential‐pulsed electrochemical deposition in a nanostructured Al₂O₃matrix. p‐type Sb₂Te₃, n‐type Bi₂Te₃, and n‐type CoSb₃thin films were grown at room temperature using molecular beam epitaxy and were subsequently annealed at elevated temperatures. This yielded polycrystalline, single phase thin films with optimized charge carrier densities. In CoSb₃thin films the speed of sound could be reduced by filling the cage structure with Yb and alloying with Fe yielded p‐type material. Bi₂(Te_0.91Se_0.09)₃/SiC and (Bi_0.26Sb_0.74)₂Te₃/SiC nanocomposites with low thermal conductivities andZTvalues larger than 1 were prepared by spark plasma sintering. Nanostructure, texture, chemical composition, as well as electronic and phononic excitations were investigated by X‐ray diffraction, nuclear resonance scattering, inelastic neutron scattering, Mössbauer spectroscopy, and transmission electron microscopy. For Bi₂Te₃materials,ab‐initiocalculations together with equilibrium and non‐equilibrium molecular dynamics simulations for point defects yielded their formation energies and their effect on lattice thermal conductivity, respectively. Current advances in thermoelectric Bi₂Te₃and CoSb₃based nanomaterials are summarized. Advanced synthesis and characterization methods and theoretical modeling were combined to assess and reduceZT‐limiting mechanisms in these materials.