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Thermoelectric materials are a unique class of compounds that can recycle energy through conversion of heat into electrical energy. A new 21–4–18 Zintl phase has been discovered in the Yb–Mn–Sb system with high performance in the mid-to-high temperature regime. The efficiency of the Yb21Mn4Sb18 results mainly from its large Seebeck coefficient (∼290 μV K–1 at 650 K) and extremely low thermal conductivity (∼0.4 W m–1 K–1). The complex crystal structure has been studied through single crystal X-ray diffraction, synchrotron powder X-ray diffraction, and pair distribution function (PDF) analysis using time-of-flight neutron diffraction revealing positional disorder on several sites. Electronic structure calculations of the band structure and the partial spin-density of states reveal that states near the Fermi level are contributed mostly by the Mn and Sb atoms that participate in the [Mn4Sb10]22– motif of the structure. The band structure confirms the p-type semiconducting nature of this material. The optimization of the hole carrier concentration was tuned according to a single parabolic band model through Na doping on the Yb site (Yb21–xNaxMn4Sb18, x = 0, 0.2, 0.4) showing an improvement in zT over the whole temperature range. A maximum zT ≈ 0.8 at 800 K is obtained for the x = 0.4 sample and increases the ZTavg from 0.34 to 0.49 (over the entire temperature range) compared to the undoped sample.
Germanium nanoclusters of average diameter 4 nm were prepared with covalently bound termination groups. Chloride-terminated nanoclusters were reacted with a Grignard reagent to form acetal-containing surface-terminated nanoclusters. Treatment with acid yielded hydroxyl-containing surface-terminated nanoclusters, and treatment with an acid bromide and base yielded an ester-containing surface-terminated nanocluster. Atom transfer radical polymerization (ATRP) was used to graft polymer chains from the surfaces of the nanoparticles to yield hybrid nanostructures. Changes of the termination group in the nanoclusters did not alter the photophysics of the original nanoclusters, a result that is consistent with a stable nanocluster surface. The nanoclusters were characterized by HRTEM (high-resolution transmission electron microscopy), NMR, FTIR, UV−vis, and fluorescence spectroscopy.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A new barium copper phosphide compound, BaCu10P4, was synthesized by reacting stoichiometric amounts of the elements at 1200 °C for 24 h. BaCu10P4 crystallizes in the monoclinic space group C2/m, with unit cell dimensions a = 23.288(4) b = 3.9070(10), and c = 9.534(2) Å and β = 92.26(2)° (Z = 4). The structure can be described as consisting of chains of edge-shared Cu4 tetrahedral prisms that are knitted together by P atoms. The structure is related to BaCu8P4, which can be described in a similar fashion. Temperature-dependent resistivity measurements indicate that BaCu10P4 is a metal. Extended Hückel band calculations are consistent with metallic character for BaCu10P4 through Cu−Cu interactions. Orbitals at the Fermi level show Cu−Cu bonding overlap. On the other hand, BaCu8P4 reveals extremely weak Cu−Cu interactions, but rather optimizes Cu−P bonding.
Synthetic organic chemists have a large toolbox of named reactions to form structural motifs through a retrosynthetic approach when targeting a complex molecule. On the other hand, a comparatively complex inorganic compound may be made through simple mechanochemical reactions of the elements followed by annealing. For complex phases that involve more than two elements, the simple mechanochemical process can be complex with many competing phases, which can negatively impact desired properties. This point has been made recently with a revelation of improved properties of thermoelectric materials upon the removal of impurities. Compounds of the Yb14AlSb11 structure type represent complex Zintl phases with exceptional high-temperature thermoelectric properties but are difficult to prepare in high purity. In this work, a quenching study was used to elucidate the pathway taken by reactions from the elements to form the complex ternary phase, Yb14AlSb11. Through that study, two Yb–Sb binary phases, Yb11Sb10 and Yb4Sb3, were identified as intermediates in the reaction. These two Yb–Sb binaries were investigated for use as reactive precursors to form Yb14MnSb11 in reactions with MnSb. Through this pseudoretrosynthetic approach, reactions from Yb4Sb3 allowed for the synthesis of high-purity Yb14MnSb11 and Yb14MgSb11 through balanced, stoichiometric reactions. The apparent Yb2O3 (∼1%) impurity found in these products was systematically reduced with x in the series Yb14-xMnSb11 (x = 0–0.05), suggesting that the main phase is inherently Yb-deficient and showing the high degree of control obtained through this synthetic approach. The stoichiometric sample of Yb14MgSb11 has a peak zT of 1.3 at 1175 K, and the stoichiometric sample of Yb14MnSb11 has a peak zT of 1.2 at 1275 K. This approach to solid-state synthesis provides reproducible products from balanced stoichiometric reactants to form high-purity complex structure types and can be adapted to other difficult ternary systems.
Abstract For high temperature thermoelectric applications, Yb 14 MnSb 11 has a maximum thermoelectric figure of merit ( zT ) of ∼1.0 at 1273 K. Such a high zT is found despite a carrier concentration that is higher than typical thermoelectric materials. Here, we reduce the carrier concentration with the discovery of a continuous transition between metallic Yb 14 MnSb 11 and semiconducting Yb 14 AlSb 11 . Yb 14 Mn 1‐x Al x Sb 11 forms a solid solution where the free carrier concentration gradually changes as expected from the Zintl valence formalism. Throughout this transition the electronic properties are found to obey a rigid band model with a band gap of 0.5 eV and an effective mass of 3 m e . As the carrier concentration decreases, an increase in the Seebeck coefficient is observed at the expense of an increased electrical resistivity. At the optimum carrier concentration, a maximum zT of 1.3 at 1223 K is obtained, which is more than twice that of the state‐of‐the‐art Si 0.8 Ge 0.2 flown by NASA.
The Zintl phase Yb(14)MnSb(11) was successfully doped with Ge utilizing a tin flux technique. The stoichiometry was determined by microprobe analysis to be Yb(13.99(14))Mn(1.05(5))Sb(10.89(16))Ge(0.06(3)). This was the maximum amount of Ge that could be incorporated into the structure via flux synthesis regardless of the amount included in the reaction. Single crystal X-ray diffraction could not unambiguously determine the site occupancy for Ge. Bond lengths varied by about 1% or less, compared with the undoped structure, suggesting that the small amount of Ge dopant does not significantly perturb the structure. Differential scanning calorimetry/thermogravimetry (DSC/TG) show that the doped compound's melting point is greater than 1200 K. The electrical resistivity and magnetism are virtually unchanged from the parent material, suggesting that Yb is present as Yb(2+) and that the Ge dopant has little effect on the magnetic structure. At 900 K the resistivity and Seebeck coefficient decrease resulting in a zT of 0.45 at 1100 K, significantly lower than the undoped compound.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIron EXAFS of the iron-molybdenum cofactor of nitrogenaseMark R. Antonio, Boon Keng Teo, W. H. Orme-Johnson, Mark J. Nelson, Susan E. Groh, Paul A. Lindahl, Susan M. Kauzlarich, and Bruce A. AverillCite this: J. Am. Chem. Soc. 1982, 104, 17, 4703–4705Publication Date (Print):August 1, 1982Publication History Published online1 May 2002Published inissue 1 August 1982https://doi.org/10.1021/ja00381a045RIGHTS & PERMISSIONSArticle Views162Altmetric-Citations47LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (385 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
Nanoscale hexagonal BN additive for ammonia borane, AB, is shown to decrease the onset temperature for hydrogen release. Both the nano-BN and the AB:nano-BN samples are prepared by ball milling. The materials are characterized by X-ray powder diffraction, 11B muclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry, and the hydrogen release is measured by a volumetric gas burette system. Several effects of the mixtures of AB:nano-BN are shown to be beneficial in comparison with neat AB. These are the decrease of the dehydrogenation temperature, the decrease in NH3 formation, as well as the decrease of the exothermicity of hydrogen release with increasing the nano-BN concentration.
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