Electronic structure and electrical transport properties of MoS2 single-walled nanotubes based on first principles

The work theoretically calculated the electronic structure and electrical transport properties of two configurations of single-walled MoS2 nanotubes: armchair nanotubes (ANTs) and zigzag nanotubes (ZNTs) based on the density functional theory and Boltzmann transport method. ANTs have an indirect one. while ZNTs have a direct bandgap structure. The Seebeck coefficient ([Formula: see text]), electrical conductivity ([Formula: see text] and power factor ([Formula: see text] were calculated as a function of carrier concentration, chemical potential and temperature using the Boltzmann transport method. The calculated power factor ([Formula: see text]) indicates that the most promising electronic properties were exhibited by [Formula: see text]-type ANTs and [Formula: see text]-type ZNTs. The [Formula: see text] of narrow bandgap (6, 6) (7, 7) (8, 8) semiconductors reached [Formula: see text], [Formula: see text] and [Formula: see text]WK[Formula: see text]m[Formula: see text] at room-temperature, respectively. (7, 7) nanotube have a maximum power factor of [Formula: see text]WK[Formula: see text]m[Formula: see text] at 950 K, and the maximum power factor of ANTs is almost twice that of ZNTs.

Backbone Effects on the Thermoelectric Properties of Ultra-Small Bandgap Conjugated Polymers

Conjugated polymers with narrower bandgaps usually induce higher carrier mobility, which is vital for the improved thermoelectric performance of polymeric materials. Herein, two indacenodithiophene (IDT) based donor–acceptor (D-A) conjugated polymers (PIDT-BBT and PIDTT-BBT) were designed and synthesized, both of which exhibited low-bandgaps. PIDTT-BBT showed a more planar backbone and carrier mobility that was two orders of magnitude higher (2.74 × 10−2 cm2V−1s−1) than that of PIDT-BBT (4.52 × 10−4 cm2V−1s−1). Both exhibited excellent thermoelectric performance after doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, where PIDTT-BBT exhibited a larger conductivity (0.181 S cm−1) and a higher power factor (1.861 μW m−1 K−2) due to its higher carrier mobility. The maximum power factor of PIDTT-BBT reached 4.04 μW m−1 K−2 at 382 K. It is believed that conjugated polymers with a low bandgap are promising in the field of organic thermoelectric materials.

Prospects for Electrical Performance Tuning in Ca3Co4O9 Materials by Metallic Fe and Ni Particles Additions

This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components, encouraged by our recent promising results obtained for similar cobalt additions. Iron and nickel were chosen because of their similarities with cobalt. The maximum power factor value of around 200 μWm−1K−2 at 925 K was achieved for the composite with the nominal nickel content of 3% vol., processed via the two-step sintering cycle, which provides the highest densification from this work. The effectiveness of the proposed approach was shown to be strongly dependent on the processing conditions and added amounts of metallic particles. Although the conventional one-step approach results in Fe- and Ni-containing composites with the major content of the thermoelectric Ca3Co4O9 phase, their electrical performance was found to be significantly lower than for the Co-containing analogue, due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively high performance of the composite with a nominal nickel content of 3% vol. processed via a two-step approach is related to the specific microstructural features from this sample, including minimal porosity and the presence of the Ca2Co2O5 phase, which partially compensate the complete decomposition of the Ca3Co4O9 matrix. The obtained results demonstrate different pathways to tailor the phase composition of Ca3Co4O9-based materials, with a corresponding impact on the thermoelectric performance, and highlight the necessity of more controllable approaches for the phase composition tuning, including lower amounts and different morphologies of the dispersed metallic phases.

More Energy-Efficient Turning

This study is a search for more energy-efficient turning enabled by optimal utilization of the machining facility’s power grid. To that end, the authors have (i) modeled the machining facility on the principles of object-oriented design; (ii) tested the model for adequacy in real-world applications; (iii) devised an approach to implementing specific processes and related design solutions for more energy-efficient machining. Cluster analysis shows that a typical turning line used in small-batch manufacturing may contain up to 20 machines with the following power distribution: 7 0.75-kW machines, 4 1.5-kW machines, 3 2.2-kW machines, 1 3-kW machine, 1 4-kW machine, 1 5.5-kW machine, 1 7.5-kW machine, and 2 11-kW machines. This configuration enables the most power-efficient turning process. The batch for turning should be distributed by the maximum power factor using the object model for the application as well as the author-developed NET-based software. In this approach, all the machines serve as cluster centers that the machined parts are grouped around to make the tur­ning process more energy-efficient by reducing the in-grid electricity loss.

Flexible thermoelectric films formed using integrated nanocomposites with single-wall carbon nanotubes and Bi2Te3 nanoplates via solvothermal synthesis

Single-wall carbon nanotubes (SWCNTs) and Bi2Te3 nanoplates are very promising thermoelectric materials for energy harvesting. When these two materials are combined, the resulting nanocomposites exhibit high thermoelectric performance and excellent flexibility. However, simple mixing of these materials is not effective in realizing high performance. Therefore, we fabricated integrated nanocomposites by adding SWCNTs during solvothermal synthesis for the crystallization of Bi2Te3 nanoplates and prepared flexible integrated nanocomposite films by drop-casting. The integrated nanocomposite films exhibited high electrical conductivity and an n-type Seebeck coefficient owing to the low contact resistance between the nanoplates and SWCNTs. The maximum power factor was 1.38 μW/(cm K2), which was 23 times higher than that of a simple nanocomposite film formed by mixing SWCNTs during drop-casting, but excluding solvothermal synthesis. Moreover, the integrated nanocomposite films maintained their thermoelectric properties through 500 bending cycles.

Enhanced Thermoelectric Performance of Indacenodithiophene-Benzothiadiazole Copolymer Containing Polar Side Chains and Single Wall Carbon Nanotubes Composites

Composite films of indacenodithiophene-bezothiadazole copolymers bearing polar side chains (P1) and single wall carbon nanotubes (SWCNTs) are found to show a competitive thermoelectric performance compared to their analogous polymers with aliphatic side chains (P2). The enhanced power factors could be attributed to the stronger interfacial interactions between the P1/SWCNTs compared to that of P2/SWCNTs containing the same ratio of SWCNTs. A maximum power factor of 161.34 μW m−1 K−2 was obtained for the composite films of P1/SWCNTs for a filler content of 50 wt%, which is higher than that of P2/SWCNTs (139.06 μW m−1 K−2, 50 wt%). Our work sheds light on the design of side-chains in efficient conjugated polymers/SWCNTs thermoelectric materials and contributes to the understanding of their thermoelectric properties.