In this work, Ag_xTe_y-Sb₂Te₃ heterostructured films are prepared by ligand exchange using hydrazine soluble metal chalcogenide. Because of the created interfacial barrier, cold carriers are more strongly scattered than hot ones and thereby an over 50% enhanced thermoelectric power factor (2 μW/(cm·K²)) is obtained at 150 °C. This shows the possibility of engineering multiphases to further improve thermoelectric performance beyond phonon scattering through a low-temperature solution processed route.

Titanate nanotubes Na_2−xH_xTi₃O₇ produced by alkali hydrothermally treated ground TiO₂ aerogels are investigated as possible materials for high-temperature thermoelectric conversion by measuring their thermoelectric properties. Strikingly, the Seebeck coefficients increased sharply in the temperature range 745 to 1032 K, reaching a maximum of 302 μV/K. The electrical resistivity of the TNNTs ranged from 325 to 525 Ωm, which is lower than that of bulk TiO₂, and thermal conductivities at room temperature were also very low, ranging from 0.55 to 0.75 Wm⁻¹ K⁻¹. The hollow structure of the titanate nanotubes, with small, uniform diameters, is thought to be responsible for the ultralow thermal conductivity. The large thermoelectric power and ultralow thermal conductivity suggest that titanate nanotubes represent a new kind of p-type oxide thermoelectric material.

We report on the enhanced thermoelectric properties of selenium (Se) doped bismuth telluride (Bi₂Te_3–xSe_x) nanoplatelet (NP) composites synthesized by the polyol method. Variation of the Se composition within NPs is demonstrated by X-ray diffraction and Raman spectroscopy. While the calculated lattice parameters closely follow the Vegard’s law, a discontinuity in the shifting of the high frequency (E_g² and A_1g²) phonon modes illustrates a two mode behavior for Bi₂Te_3–xSe_x NPs. The electrical resistivity (ρ) of spark plasma sintered pellet composites shows metallic conduction for pure Bi₂Te₃ NP composites and semiconducting behavior for intermediate Se compositions. The thermal conductivity (κ) for all NP composites is much smaller than the bulk values and is dominated by microstructural grain boundary scattering. With temperature dependent electrical and thermal transport measurements, we show that both the thermoelectric power S (−259 μV/K) and the figure of merit ZT (0.54) are enhanced by nearly a factor of 4 for SPS pellets of Bi₂Te_2.7Se_0.3 in comparison to Bi₂Te₃ NP composites. Tentatively, such an enhancement of the thermoelectric performance in nanoplatelet composites is attributed to the energy filtering of low energy electrons by abundant grain boundaries in aligned nanocomposites.

The field of thermoelectrics has progressed enormously and is now growing steadily because of recently demonstrated advances and strong global demand for cost-effective, pollution-free forms of energy conversion. Rapid growth and exciting innovative breakthroughs in the field over the last 10–15 years have occurred in large part due to a new fundamental focus on nanostructured materials. As a result of the greatly increased research activity in this field, a substantial amount of new data—especially related to materials—have been generated. Although this has led to stronger insight and understanding of thermoelectric principles, it has also resulted in misconceptions and misunderstanding about some fundamental issues. This article sets out to summarize and clarify the current understanding in this field; explain the underpinnings of breakthroughs reported in the past decade; and provide a critical review of various concepts and experimental results related to nanostructured thermoelectrics. We believe recent achievements in the field augur great possibilities for thermoelectric power generation and cooling, and discuss future paths forward that build on these exciting nanostructuring concepts.

Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit,ZT, whereZ is a measure of a material's thermoelectric properties andT is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then—despite investigation of various approaches—there has been only modest progress in finding materials with enhancedZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement inZT at 300 K, compared to state-of-the-art bulk Bi₂Te₃ alloys. This amounts to a maximum observed factor of2.4 for our p-type Bi₂Te₃/Sb₂Te₃ superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm^-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.

We studied the cross-plane lattice and electronic thermal conductivities of superlattices made of InGaAlAs and InGaAs films, with the latter containing embedded ErAs nanoparticles (denoted as ErAs:InGaAs). Measurements of total thermal conductivity at four doping levels and a theoretical analysis were used to estimate the cross-plane electronic thermal conductivity of the superlattices. The results show that the lattice and electronic thermal conductivities have marginal dependence on doping levels. This suggests that there is lateral conservation of electronic momentum during thermionic emission in the superlattices, which limits the fraction of available electrons for thermionic emission, thereby affecting the performance of thermoelectric devices.

We report the synthesis of highly crystallographically textured films of stoichiometric bismuth telluride (Bi₂Te₃) in the presence of a surfactant, sodium lignosulfonate (SL), that resulted in the improved alignment of films in the (110) plane and offered good control over the morphology and roughness of the electrodeposited films. SL concentrations in the range 60–80 mg dm^–3 at a deposition potential of −0.1 V vs SCE (saturated calomel electrode) were found to yield the most improved crystallinity and similar or superior thermoelectric properties compared with results reported in the literature.

n-type and p-type thermoelectric thin films have been deposited by direct current magnetron sputtering from n-type Bi₂Te_2.7Se_0.3 and p-type Bi_0.5Sb_1.5Te₃ targets on glass and Al₂O₃ substrates. X-ray diffraction and energy dispersive spectrometry combined with electrical measurements such as Seebeck coefficient and electrical resistivity were used for the thermoelectric thin films characterization. It was found that the composition of the sputtered thin films was close to the sputtering target stoichiometry for the tested deposition conditions and that the thin film composition did not seem to be the determinant parameter for the thermoelectrical properties. Indeed, the chamber pressure and plasma power have a greater influence on the thermoelectrical performances of the films. Annealing in Ar atmosphere (250 °C for n-type and 300 °C for p-type films) enhanced the film crystallization and yield power factors higher than 1 mW/K² m.

Indium tin oxide (ITO) thin films were grown on SiO₂ glass and silicon (Si) substrates from a 95 wt% In₂O₃–5 wt% SnO₂ sintered ceramic target by pulsed laser deposition (PLD). The films were deposited under different oxygen pressures (P_o2) of 5×10^-3 to 5×10^-2 Torr at room temperature (RT) and 200°C.P_o2 was found to have a critical influence on the optical and the electrical properties of the ITO films. Under aP_o2 of 1×10^-2 Torr, ITO films with resistivity as low as 4.5×10^-4 and 1.8×10^-4 Ωcm were obtained on glass at RT and 200°C, respectively. Moreover, by increasing the substrate temperature (T_s) to 350°C, the resistivity was further reduced to 1.3×10^-4 Ωcm. Optical transmittance in visible light greater than 85% was attained in all the films deposited underP_o2 above 5× 10^-3 Torr. However, a reduction in the transmittance to less than 80% was observed asP_o2 decreased. The films deposited at RT were amorphous, whereas those produced at 200°C were polycrystalline.

Large-scale, well-aligned CdTenanowire arrays with different crystallographic phases have been prepared simply by regulating the basic growth parameters of the sputtering method. Pure zinc blende phasenanowire arrays that propagate in the (111) direction are achieved using a high growth temperature coupled with a low deposition rate. Conversely, wurtzite phasenanowire arrays with growth in the (002) direction have also been prepared by using a lower growth temperature and higher deposition rate. A Gibbs free energy nucleation model is use to explain the formation of these different crystal phases under the growth conditions employed. The differences in crystal structure are shown to exhibit different energy bands, defects and carrier transport properties. The wurtzite phase, with a narrower band gap (1.64 eV), is found to have better photoelectric properties than those of the zinc blende phase.