Colossal Seebeck coefficient in Aurivillius Phase-Perovskite Oxide Composite

We propose an inexpensive scalable approach for achieving extremely high values of Seebeck coefficient ($\alpha$) by exploiting the natural superlattice structure in Aurivillius phase oxides. In particular, we report an $\alpha \approx$ 319\,mV/K at 300\,K in a composite of Aurivillius phase compound SrBi$_4$Ti$_4$O$_{15}$ (as a matrix) and a perovskite phase material (e.g., La$_{0.7}$Sr$_{0.3}$MnO$_3$ or, La$_{0.7}$Sr$_{0.3}$CoO$_3$ as filler). Such a colossal value of $\alpha$ can be attributed to contributions from the enhanced density of states due to the effective low dimensional character of Bi$_2$O$_2$ layer. The corresponding thermal conductivity ($\kappa$) and the electrical conductivity ($\sigma$) lies in the range 0.7 - 1.25 W/m-K and 10 - 100 $\mu$S/m, respectively at 300\,K. Attributed to the high $\alpha$ values, such oxide composites can be used as thermopile sensors and highly sensitive bolometric applications. We anticipate that the demonstration of colossal $\alpha$ in oxide composites using a simple synthesis strategy also sets the stage for future material innovations for high temperature thermoelectric applications.Comment: 5 figures, 1 tabl

Improved Thermoelectric Properties in (1-x)LaCoO3/(x)La0.7Sr0.3CoO3 Composite

A high Seebeck coefficient (S), large electrical conductivity ({\sigma}), and reduced thermal conductivity ({\kappa}) are required to achieve a high figure-of-merit (zT) in an ideal thermoelectric (TE) system, which is challenging in a single system due to the interdependence of TE parameters. Composite approach is promising to manipulate the TE parameters. In this study, TE properties of (1-x)LaCoO3/(x)La0.7Sr0.3CoO3 (0.00 \leq x \leq 0.05) composite is discussed. The structural analysis confirms individual phases in the composite, which is further supported by electron microscopy analysis. The x-ray photoelectron analysis indicates that oxygen vacancies (VO) are present in the parent LaCoO3 system and increase with the addition of La0.7Sr0.3CoO3 (LSCO) in the composite. The increase in VO raises the degenerate states of cobalt and hence improves S in the composites. Temperature variation in S and {\sigma} are consistent with the spin-state transition and shows the correlation between these two parameters. The reduction in {\kappa} and {\sigma} with the addition of ball-milled La0.7Sr0.3CoO3 in the composite is attributed to the enhanced phonon-phonon and charge carrier scattering, respectively. A synergistic effect of enhanced S and reduced \kappa} result in five times improvement in zT of the composite compared to the parent LaCoO3 system at 800 K. This approach also improves the operating temperature for LaCoO3 based systems.Comment: 26 pages, 10 figures, 4 table

Automotive Waste Heat Recovery by Thermoelectric Generator Technology

Automotive exhaust thermoelectric generators (AETEG) are gaining significant importance wherein a direct conversion of exhaust waste heat into electricity allows for a reduction in fuel consumption. Over the past two decades, extensive progress has been made in materials research, modules and thermoelectric generator (TEG) system. Many prototypes using BiTe, CoSb3 and half Heusler materials have been developed and tested for efficiency in different engines. The role of exhaust flow rate, temperature and heat exchanger type on the performance of AETEG is investigated deeply. This chapter reviews the progress made so far in the AETEG technology. Section 1 gives a brief introduction; section 2 gives a description of the technology and section 3, the construction details of a typical AETEG. The performance evaluation of AETEG is discussed in Section 4, application of TEG using engine coolant heat is discussed in Section 5 and TEGs for hybrid vehicles are described in Section 6. The parasitic losses due to AETEG and the conditioning of the power produced for practical applications using the maximum power point tracking technique are discussed in Sections 7 and 8, respectively. Finally, in Section 9, cost analysis and the challenges associated with the commercialization of AETEG is presented

Thermoelectric Properties of (1-x)LaCoO3.x_{3.x}La0.7_{0.7}Sr0.3_{0.3}MnO3_3 Composite

We report the thermoelectric (TE) properties of (1-x)LaCoO3.xLa0.7Sr0.3MnO3 (0 < x < 0.10) composite in a temperature range 320-800 K. Addition of La0.7Sr0.3MnO3 to LaCoO3 in small amount (5 weight %) improves the overall Seebeck coefficient ({\alpha}) at higher temperatures. The electrical conductivity, however, decreases due to a decrease in carrier concentration of the composite. The decrease in electrical conductivity of the composite at high temperature may be attributed to the insulating nature of the LSMO above room temperature. Thermal conductivity (\k{appa}) of all the samples increases with an increase in the temperature but decreases with increasing LSMO content. We also report the local variation of the Seebeck coefficient across the composite samples measured using a precision Seebeck measurement system. A maximum value of 0.09 for the figure of merit (ZT) is obtained for 0.95LaCoO3.0.05La0.7Sr0.3MnO3 at 620 K which is significantly higher than the ZT of either of LaCoO3 or La0.7Sr0.3MnO3 at 620 K. This suggests the potential for enhancement of operating temperatures of hitherto well known low-temperature thermoelectric materials through suitable compositing approach.Comment: 16 pages, 7 figures, 2 tables. arXiv admin note: text overlap with arXiv:1807.0556

Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies

The aim of present work is to study the effect of VC and/or Cr3C2 in densification, microstructural development and mechanical behavior of nanocrystalline WC-12wt.%Co powders when they are sintered by spark plasma sintering (SPS) and hot isostatic pressing (HIP). The results were compared to those corresponding to conventional sintering in vacuum. The density, microstructure, X-ray diffraction, hardness and fracture toughness of the sintered materials were evaluated. Materials prepared by SPS exhibits full densification at lower temperature (1100 degrees C) and a shorter stay time (5 min), allowing the grain growth control. However, the effect of the inhibitors during SPS process is considerably lower than in conventional sintering. Materials prepared by HIP at 1100 degrees C and 30 min present full densification and a better control of microstructure in the presence of VC. The added amount of VC allows obtaining homogeneous microstructures with an average grain size of 120 nm. The hardness and fracture toughness values obtained were about 2100 HV30 and close to 10 MPa m(1/)2, respectively. (C) 2010 Elsevier Ltd. All rights reserved.The work is supported financially by the Spanish Ministry of Science and Innovation by means of the project MAT 2006-12945-C03-C02 and MAT 2009-14144-C03-C02.Bonache Bezares, V.; Salvador Moya, MD.; Fernández Valdés, A.; Borrell Tomás, MA. (2011). Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies. International Journal of Refractory Metals and Hard Materials. 29(2):202-208. https://doi.org/10.1016/j.ijrmhm.2010.10.007S20220829

New Signatures of Bio-Molecular Complexity in the Hypervelocity Impact Ejecta of Icy Moon Analogues

Impact delivery of prebiotic compounds to the early Earth from an impacting comet is considered to be one of the possible ways by which prebiotic molecules arrived on the Earth. Given the ubiquity of impact features observed on all planetary bodies, bolide impacts may be a common source of organics on other planetary bodies both in our own and other solar systems. Biomolecules such as amino acids have been detected on comets and are known to be synthesized due to impact-induced shock processing. Here we report the results of a set of hypervelocity impact experiments where we shocked icy mixtures of amino acids mimicking the icy surface of planetary bodies with high-speed projectiles using a two-stage light gas gun and analyzed the ejecta material after impact. Electron microscopic observations of the ejecta have shown the presence of macroscale structures with long polypeptide chains revealed from LCMS analysis. These results suggest a pathway in which impact on cometary ices containing building blocks of life can lead to the synthesis of material architectures that could have played a role in the emergence of life on the Earth and which may be applied to other planetary bodies as well. View Full-Tex

Enhanced ferroelectricity and magnetoelectricity in 0.75BaTiO3-0.25BaFe12O19 by spark plasma sintering

Spark Plasma Sintering (SPS) technique was employed to synthesize 0.75BaTiO3-0.25BaFe12O19 composite. X-ray diffraction studies revealed that the composite consisted of both BaTiO3 (ferroelectric phase) andBaFe12O19 (ferrimagnetic phase), respectively. The SPS treated sample showed improved ferroelectric nature when compared to conventional sintered (CS) sample. Transformation from hard to soft magnetic nature was envisaged by magnetization measurements for SPS sample. A slim hysteresis loop was recorded with a low coercivity values (390 Oe) when compared to CS sample (3900 Oe). Mossbauer spectroscopy analysis indicated that the existence of a partial amount of γ-Fe2O3 phase in the lattice, giving rise to soft magnetic nature. The SPS sample showed slightly higher value of magnetoelectric output of 2.95 mV/cm at 3 kOe magnetic field when compared to the CS sample (1.45 mV/cm at 3 kOe). The present investigation compares the spark plasma sintered sample with the conventional sintered sample

Role of Cu During Sintering of Fe0.96Cu0.04 Nanoparticles

Nanoparticle agglomerates of passivated Fe (n-Fe) and Fe0.96Cu0.04 (n-Fe0.96Cu0.04), synthesized through the levitational gas condensation (LGC) process, were compacted and sintered using the conventional powder metallurgy method. The n-Fe0.96Cu0.04 agglomerates produced lower green density than n-Fe, and when compacted under pressure beyond 200 MPa, they underwent lateral cracking during ejection attributed to the presence of a passive oxide layer. Sintering under dynamic hydrogen atmosphere can produce a higher density of compact in n-Fe0.96Cu0.04 in comparison to n-Fe. Both the results of dilatometry and thermogravimetric (TG) measurements of the samples under flowing hydrogen revealed enhancement of the sintering process as soon as the reduction of oxide layers could be accomplished. The shrinkage rate of n-Fe0.96Cu0.04 reached a value three times higher than n-Fe at a low temperature of 723 K (450 A degrees C) during heating. This enhanced shrinkage rate was the manifestation of accumulation of Cu at the surface of the particles. The formation of a thin-surface melted layer enriched with copper during heating to isothermal holding facilitated as a medium of transport for diffusion of the elements. The compacts produced by sintering at 773 K (500 A degrees C), with relative density 82 pct, were found to be unstable and oxidized instantly when exposed to ambient atmosphere. The stable compacts of density more than 92 pct with 300- to 450-nm grain size could only be produced when sintering was carried out at 973 K (700 A degrees C) and beyond. The 0.22 wt pct residual oxygen obtained in the sintered compact is similar to what is used for conventional ferrous powder metallurgy products

Development of Ni-Al<SUB>2</SUB>O<SUB>3</SUB>in-situ nanocomposite by reactive milling and spark plasma sintering

In the present study, Ni-30 vol pct Al2O3 in-situ nanocomposite was developed by reactive milling of NiO-Al-Ni powder mixture followed by spark plasma sintering (SPS). During milling, fcc to hcp transformation was observed in Ni(Al) phase and it transformed back to fcc phase around 773 K (500 &#176;C). The hardness and yield strength of Ni-30 vol pct Al2O3 nanocomposite are approximately two times higher than that of pure Ni of similar grain size. The improved mechanical properties of nanocomposite are attributed to the presence of alumina particles of nanometer size