From thermoelectric bulk to nanomaterials: Current progress for Bi₂Te₃ and CoSb₃

Abstract

Bi2Te3 and CoSb3 based nanomaterials were synthesized and their thermoelectric, structural, and vibrational properties analyzed to assess and reduce ZT‐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 Bi38Te55Se7 nanowires with power factors comparable to nanostructured bulk materials were prepared by potential‐pulsed electrochemical deposition in a nanostructured Al2O3 matrix. p‐type Sb2Te3, n‐type Bi2Te3, and n‐type CoSb3 thin 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 CoSb3 thin films the speed of sound could be reduced by filling the cage structure with Yb and alloying with Fe yielded p‐type material. Bi2(Te0.91Se0.09)3/SiC and (Bi0.26Sb0.74)2Te3/SiC nanocomposites with low thermal conductivities and ZT values 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 Bi2Te3 materials, ab‐initio calculations 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 Bi2Te3 and CoSb3 based nanomaterials are summarized. Advanced synthesis and characterization methods and theoretical modeling were combined to assess and reduce ZT‐limiting mechanisms in these materials.

Enhanced figure of merit in nanostructured (Bi,Sb)2Te3 with optimized composition, prepared by a straightforward arc-melting procedure

“…6b ), reaching a maximum of 209 μV K −1 in Bi 0.5 Sb 1.5 Te 3 at 395 K, as checked in several samples. Pristine Bi 2 Te 3 is an n-type semiconductor, with Seebeck-coefficients in the range −50 to −260 μV K −1 17 , 36 , 37 . The literature indicates that as Bi 3+ is progressively replaced by Sb 3+ , the sign of the conduction carriers becomes positive, reaching a maximum value 250 μV K −1 at 320 K 35 , 38 , for bulk samples prepared by mechanical alloying and SPS, corresponding to a nominal composition of Bi 0.5 Sb 1.5 Te 3 .…”

Nanostructured State-of-the-Art Thermoelectric Materials Prepared by Straight-Forward Arc-Melting Method

“…In bismuth telluride samples, charge carriers concentration is strongly affected by antisite Bi Te and Te Bi defects, which are randomly created during synthesis process. This feature yields a wide range of Seebeck coefficient values measured in samples prepared by different methods [15,[34][35][36][37][38][39].…”

Hydrogenation and oxidation enhances the thermoelectric performance of Si2BN monolayer

“…Thermal conductivity contains both lattice and electronic parts; k = k l +k e , k l is lattice thermal conductivity relative to lattice vibrations (phonon), and k e is electronic thermal conductivity related to electronic structure. Over the last many years, intensive research has been done to increase ZT for high thermoelectric performance [8][9][10][11][12][13][14][15][16][17]. It was previously reported that graphene and boron nitride have very high formation energy.…”