Thermoelectric Performance of Polypropylene/Carbon Nanotube/Ionic Liquid Composites and Its Dependence on Electron Beam Irradiation

The thermoelectric behavior of polypropylene (PP) based nanocomposites containing single walled carbon nanotubes (SWCNTs) and five kinds of ionic liquids (Ils) dependent on composite composition and electron beam irradiation (EB) was studied. Therefore, several samples were melt-mixed in a micro compounder, while five Ils with sufficiently different anions and/or cations were incorporated into the PP/SWCNT composites followed by an EB treatment for selected composites. Extensive investigations were carried out considering the electrical, thermal, mechanical, rheological, morphological and, most significantly, thermoelectric properties. It was found that it is possible to prepare n-type melt-mixed polymer composites from p-type commercial SWCNTs with relatively high Seebeck coefficients when adding four of the selected Ils. The highest Seebeck coefficients achieved in this study were +49.3 µV/K (PP/2 wt.% SWCNT) for p-type composites and −27.6 µV/K (PP/2 wt.% SWCNT/4 wt.% IL type AMIM Cl) for n-type composites. Generally, the type of IL is decisive whether p- or n-type thermoelectric behavior is achieved. After IL addition higher volume conductivity could be reached. Electron beam treatment of PP/SWCNT leads to increased values of the Seebeck coefficient, whereas the EB treated sample with IL (AMIM Cl) shows a less negative Seebeck coefficient value.

First-principles study of the structural and thermoelectric properties of Y-doped α-SrSi2

The narrow-gap semiconductor α-SrSi2 is a promising candidate for low-temperature thermoelectric applications with low environmental load. The only experimental report in which α-SrSi2 is reported to have n-type conductivity is one where it had been doped with yttrium. To further clarify the effects of impurities, theoretical studies are needed. The α-SrSi2 has a very narrow band gap (~13–35 meV), causing difficulties in the accurate calculation of the electronic and thermoelectric properties. In our previous study, we overcame this problem for undoped α-SrSi2 using hybrid functional theory. We used this method in this study to investigate the structures, energetic stabilities, electronic structures, and thermoelectric properties of Y-doped α-SrSi2. The results indicate that substitution at Sr-sites is energetically about two times more stable than that at Si-sites. Furthermore, negative Seebeck coefficients were obtained at low temperatures and reverted to p-type with increasing temperature, which is consistent with the experimental results.

Research on the performance of two different porphin graphene nanoribbons coupled thermoelectric devices

The effect of bonding position on the energy conversion efficiency of porphin graphene nanoribbons coupled thermoelectric devices was studied by the first-principles. The results show that the change of bonding position can greatly adjust the lattice thermal conductivity of the coupled thermoelectric devices; although the change of bonding position has no obvious effect on the transport properties of holes in the coupled structure, it can obviously adjust the transport properties of electrons, resulting in the different Seebeck coefficients and quality merit values of different coupled thermoelectric devices The results illustrate the different thermoelectric energy conversion effects in different porphin graphene nanoribbons coupled thermoelectric devices with different bonding positions, which provides an effective theoretical basis for the design of thermoelectric quantum devices based on graphene nanoribbons.

CsPd0.875Cr0.125I3 Promising Candidate for Thermoelectric Applications

We study the electronic structure, magnetization, and thermoelectric properties of CsPd0.875Cr0.125I3 obtained by doping CsPdI3 with atoms of the 3d transition metal Cr. By applying the generalized-gradient-approximation (GGA) and the GGA + U one, we found that CsPd0.875Cr0.125I3 alloy exhibits a completely metallic characteristic. Changes in the thermoelectric properties of the alloy are determined with the use of the BoltzTrap code. The electronic thermal conductivities (k/т), Seebeck coefficients (S), power factors (PF), and electrical conductivities (q/т) are calculated. The value of the ZT merit factor is near 1 at room temperature, by indicating that CsPd0.875Cr0.125I3 is a good candidate for thermoelectric applications at high and low temperatures.

The Effects of Ba0.85Ca0.15Zr0.1Ti0.9O3 Addition on the Phase, Microstructure, and Thermoelectric Properties of Ca3Co4O9 Ceramics

In this work, the influences of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) addition on phase, microstructure, and thermoelectric properties of Ca3Co4O9 (CCO) were investigated. (1-x)CCO-(x)BCZT ceramics where x = 0, 0.003, 0.005, and 0.010 were fabricated successfully via a conventional solid-state sintering at 1,223 K for 24 hrs. The substitution of BCZT introduced the chemical defects (V''Co, V'''Co, V''Ca) in CCO ceramic, which increased charge carrier concentration and enhanced the electrical conductivity. The presence of Co3+ improved the Seebeck coefficients of CCO ceramic. The thermal conductivity of CCO ceramic decreased when BCZT was added. The addition of BCZT at x = 0.010 promoted the highest thermoelectric power factor (PF~235 mW/mK2), and the highest figure of merit (ZT~0.5) at 800 K, which present this ceramic an alternative p-type oxide thermoelectric for a high-temperature thermoelectric device.

First-principles study of electronic structures, thermodynamic, and thermoelectric properties of the new Rattling Full Heusler compounds Ba2AgZ (Z = As, Sb, Bi)

The ab initio calculations based on the density functional theory (DFT) using the self-consistent Full potential linearized augmented plane wave (FPLAPW) method were performed to explore the electronic structures, thermodynamic and thermoelectric properties of new rattling Full Heusler alloys Ba2AgZ (Z = As, Sb, Bi). Results showed that the AlCu2Mn-type structure state is energetically the most stable structure. The results show that the electronic property of these cubic Rattling Heusler alloys have a semiconducting behavior with indirect band gaps Eg (L-D). The predicted band gaps were found to be 0.566, 0.548 and 0.433 eV for Z = As, Sb and Bi, respectively. The thermodynamic properties comprising the thermal expansion coefficient, heat capacity, entropy and Debye temperature parameter were evaluated at various pressures from 0 to 15 GPa. Thermoelectric properties of the Ba2AgZ (Z= As, Sb, Bi) materials are additionally computed over an extensive variety of temperature and it is discovered that all compounds exhibit ultralow thermal conductivity, good Seebeck coefficients and large high power factors, thus resulting they are suitable for use in thermoelectric device applications.

Preparation of n-type polyaniline/hexagonal boron nitride composites with a large thermoelectric power factor

In the present study, it was aimed to investigate the thermoelectric (TE) properties of polyaniline/hexagonal boron nitride (PANI/h-BN) composites. First, h-BN was synthesized from boric acid and urea. Then, PANI-HCl was synthesized by oxidative chemical polymerization. Finally, the composites were prepared using different weight ratios of h-BN. The composites were characterized using attenuated total reflection accessory attached Fourier-transform infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, and scanning electron microscopy/energy dispersive X-ray analyzer. TE investigation of the composites showed that the addition of h-BN significantly contributes to the TE properties of PANI-HCl. The addition of h-BN increased the power factor of PANI-HCl from 0.07 μWm−1K−2 to 143.05 μWm−1K−2. Furthermore, all the composites showed negative Seebeck coefficients which are the characteristics of n-type semiconductors.

Charge Transport and Thermoelectric Properties of Sn-Doped Tetrahedrites Cu12Sb4-ySnyS13

In this study, tetrahedrite compounds doped with Sn were prepared by mechanical alloying and hot pressing, and their charge transport and thermoelectric properties were analyzed. X-ray diffraction analysis revealed that both the synthetic powders and sintered bodies were synthesized as a single tetrahedrite phase without secondary phases. Densely sintered specimens were obtained with relatively high densities of 99.5%-100.0% of the theoretical density, and the component elements were distributed uniformly. Sn was successfully substituted at the Sb site, and the lattice constant increased from 1.0348 to 1.0364 nm. Positive signs of the Hall and Seebeck coefficients confirmed that the Sn-doped tetrahedrites were p-type semiconductors. The carrier concentration decreased from 1.28 × 1019 to 1.57 × 1018 cm-3 as the Sn content decreased because excess electrons were supplied by doping with Sn4+ at the Sb3+ site of the tetrahedrite. The Seebeck coefficient increased with increasing Sn content, and Cu12Sb3.6Sn0.4S13 exhibited maximum values of 238-270 µVK-1 at temperatures of 323-723 K. However, the electrical conductivity decreased as the amount of Sn doping increased. Thus, Cu12Sb3.9Sn0.1S13 exhibited the highest electrical conductivity of (2.24-2.40) × 104 Sm-1 at temperatures of 323-723 K. A maximum power factor of 0.73 mWm-1K-2 was achieved at 723 K for Cu12Sb3.9Sn0.1S13. Sn substitution reduced both the electronic and lattice thermal conductivities. The lowest thermal conductivity of 0.49-0.60 Wm-1K-1 was obtained at temperatures of 323-723 K for Cu12Sb3.6Sn0.4S13, where the lattice thermal conductivity was dominant at 0.49-0.57 Wm-1K-1. As a result, a maximum dimensionless figure of merit of 0.66 was achieved at 723 K for Cu12Sb3.9Sn0.1S13.

Charge Transport and Thermoelectric Properties of Sn-Doped Tetrahedrites Cu12Sb4-ySnyS13

In this study, tetrahedrite compounds doped with Sn were prepared by mechanical alloying and hot pressing, and their charge transport and thermoelectric properties were analyzed. X-ray diffraction analysis revealed that both the synthetic powders and sintered bodies were synthesized as a single tetrahedrite phase without secondary phases. Densely sintered specimens were obtained with relatively high densities of 99.5%-100.0% of the theoretical density, and the component elements were distributed uniformly. Sn was successfully substituted at the Sb site, and the lattice constant increased from 1.0348 to 1.0364 nm. Positive signs of the Hall and Seebeck coefficients confirmed that the Sn-doped tetrahedrites were p-type semiconductors. The carrier concentration decreased from 1.28 × 1019 to 1.57 × 1018 cm-3 as the Sn content decreased because excess electrons were supplied by doping with Sn4+ at the Sb3+ site of the tetrahedrite. The Seebeck coefficient increased with increasing Sn content, and Cu12Sb3.6Sn0.4S13 exhibited maximum values of 238-270 µVK-1 at temperatures of 323-723 K. However, the electrical conductivity decreased as the amount of Sn doping increased. Thus, Cu12Sb3.9Sn0.1S13 exhibited the highest electrical conductivity of (2.24-2.40) × 104 Sm-1 at temperatures of 323-723 K. A maximum power factor of 0.73 mWm-1K-2 was achieved at 723 K for Cu12Sb3.9Sn0.1S13. Sn substitution reduced both the electronic and lattice thermal conductivities. The lowest thermal conductivity of 0.49-0.60 Wm-1K-1 was obtained at temperatures of 323-723 K for Cu12Sb3.6Sn0.4S13, where the lattice thermal conductivity was dominant at 0.49-0.57 Wm-1K-1. As a result, a maximum dimensionless figure of merit of 0.66 was achieved at 723 K for Cu12Sb3.9Sn0.1S13.

Investigation on the Power Factor of Skutterudite Smy(FexNi1-x)4Sb12 Thin Films: Effects of Deposition and Annealing Temperature

Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Smy(FexNi1-x)4Sb12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity σ and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348–523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity.