Search

Most of the state-of-the-art thermoelectric materials are inorganic semiconductors. Owing to the directional covalent bonding, they usually show limited plasticity at room temperature1,2, for example, with a tensile strain of less than five per cent. Here we discover that single-crystalline Mg3Bi2 shows a room-temperature tensile strain of up to 100 per cent when the tension is applied along the (0001) plane (that is, the ab plane). Such a value is at least one order of magnitude higher than that of traditional thermoelectric materials and outperforms many metals that crystallize in a similar structure. Experimentally, slip bands and dislocations are identified in the deformed Mg3Bi2, indicating the gliding of dislocations as the microscopic mechanism of plastic deformation. Analysis of chemical bonding reveals multiple planes with low slipping barrier energy, suggesting the existence of several slip systems in Mg3Bi2. In addition, continuous dynamic bonding during the slipping process prevents the cleavage of the atomic plane, thus sustaining a large plastic deformation. Importantly, the tellurium-doped single-crystalline Mg3Bi2 shows a power factor of about 55 microwatts per centimetre per kelvin squared and a figure of merit of about 0.65 at room temperature along the ab plane, which outperforms the existing ductile thermoelectric materials3,4.The thermoelectric material Mg3Bi2 is shown to be ductile in single-crystal form along certain directions, with a room-temperature tensile strain of 100%, which is attributed to the gliding of dislocations. [ABSTRACT FROM AUTHOR]

Mg3(Sb, Bi)2‐based materials possess excellent room‐temperature thermoelectric performance, while poor interfacial behaviors occur when connected with metal electrodes due to the strong chemical activity and volatility of Mg element. In this study, a high efficiency of 7.1% under a temperature difference of 230 K is achieved in n‐Mg3(Sb, Bi)2/p‐Bi2Te3 thermoelectric module. When changing the interfacial layer from Fe powder to Fe foil, it effectively prevents a significant diffusion of both Mg and Bi elements from the material matrix to the interfacial layer, resulting in an extremely low contact resistivity ≈3.4 µΩ cm2 that is almost one order lower than of that of Fe powder/Mg3(Sb, Bi)2 junction ≈30 µΩ cm2. Particularly, a thin diffusion layer with a width of ≈2 µm is initially observed in the unannealed Fe foil/Mg3(Sb, Bi)2 junction. Even after thermal aging at 573 K for 28 days, the diffusion‐layer width is basically unchanged and its corresponding contact resistivity maintained as low as ≈5.8 µΩ cm2. Overall, this work provides deep insights into interfacial design and paves the way for high‐performance and sustainable low‐grade waste heat recovery. [ABSTRACT FROM AUTHOR]

Bismuth telluride alloys favor the applications of low‐grade waste heat recovery if their figure‐of‐merits are improved within the larger temperature range from 300 to 523 K. Herein, this work reports a synergistic optimization for Bi0.5Sb1.5Te3 (BST) by incorporating the copper(II) phthalocyanine (CuPc), which is preferentially distributed at the grain boundary of BST after the spark plasma sintering process and suppresses the grain growth of BST. The lattice thermal conductivity of composites is then extensively reduced by the multiscale scattering induced by the CuPc. In addition, the Cu atoms diffuse into the lattice of BST and increase the whole concentration, thus suppressing the bipolar effect. As a result, the average zT value is effectively enhanced from 0.7 to 1.1 in the temperature range between 300 and 523 K. A high conversion efficiency of 6.8% is achieved in a single BST/CuPc5 leg, which is 41.7% higher than that of BST at temperature different ΔT = 223 K. This result proves that the composition optimization of the BST/CuPc is a promising strategy to improve the application of BST‐based TE modules. [ABSTRACT FROM AUTHOR]

Diffusion barrier film was strongly proposed to utilize in Bi2Te3-based thermoelectric (TE) module. However, effects of different barriers on microstructures of solder joints and electrical properties of TE modules were still unclear, which were vital in practical applications. In current work, Bi2Te3-based TE modules without barrier (TM), with Ni (TMNi) and with Ni/Au (TMNi/Au) were fabricated via reflow-soldering. Experimental results revealed that at the interface between SAC305 solder and P- or N- type Bi2Te3 sample, the Ni or Ni/Au barrier could efficiently inhibit severe growth of the intermetallic compound (IMC) phase. Remarkably, a thinner IMC layer was observed at the solder/Au/Ni/Bi2Te3 interface, which was attributed to effects of Au elements on suppressing the formation of IMCs. The results of power generation ability test revealed that TMNi exhibited higher value of output power (P) under the temperature difference (ΔT) due to its higher values of open circuit voltage (V) and output current (I). On the other hand, since the lowest electrical resistance (R) and relatively low output current of TMNi/Au were measured during the test, the TMNi/Au was suggested to generate less heat, meaning it consumed less energy, and hence be theoretically more efficient in improving the conversion efficiency. [ABSTRACT FROM AUTHOR]

This research systematically investigated three joint systems (SAC305/Bi2(Te,Se)3, SAC305/Ni/Bi2(Te,Se)3 and SAC305/Cu/Bi2(Te,Se)3) and compared the influence of Ni and Cu electrodeposits on the interfacial reaction. The thermoelectric material possessed an isotropic microstructure, and hence its surface had no significantly effects on deposited direction of Ni or Cu atoms. The crystal orientations of Ni and Cu grains were indexed to be (111) and (200), and no noticeable impure products were formed in these two electrodeposits. Compared with the defective Cu plating, fully crystallization of the Ni plating was more beneficial to the spreadability of solder, and this advantage could dramatically promote the reliability of solder joints. Under aging treatment at 160 °C for various hours to 360 h, heterogenetic compounds grew excessively in the SAC305/Bi2(Te,Se)3 couple, which could result in brittle failure. This reliability of this joint system was improved by depositing Ni or Cu on the substrate. However, the poor interfacial contact between the Cu coating and TE substrates severely resulted in the deterioration of mechanical properties of solder joints. In contrast, the SAC305/Ni/Bi2(Te,Se)3 system were more reliable during the whole aging period. [ABSTRACT FROM AUTHOR]

The dentate gyrus (DG) controls information flow into the hippocampus and is critical for learning, memory, pattern separation, and spatial coding, while DG dysfunction is associated with neuropsychiatric disorders. Despite its importance, the molecular mechanisms regulating DG neural circuit assembly and function remain unclear. Here, we identify the Rac-GEF Tiam1 as an important regulator of DG development and associated memory processes. In the hippocampus, Tiam1 is predominantly expressed in the DG throughout life. Global deletion of Tiam1 in male mice results in DG granule cells with simplified dendritic arbors, reduced dendritic spine density, and diminished excitatory synaptic transmission. Notably, DG granule cell dendrites and synapses develop normally in Tiam1 KO mice, resembling WT mice at postnatal day 21 (P21), but fail to stabilize, leading to dendrite and synapse loss by P42. These results indicate that Tiam1 promotes DG granule cell dendrite and synapse stabilization late in development. Tiam1 loss also increases the survival, but not the production, of adult-born DG granule cells, possibly because of greater circuit integration as a result of decreased competition with mature granule cells for synaptic inputs. Strikingly, both male and female mice lacking Tiam1 exhibit enhanced contextual fear memory and context discrimination. Together, these results suggest that Tiam1 is a key regulator of DG granule cell stabilization and function within hippocampal circuits. Moreover, based on the enhanced memory phenotype of Tiam1 KO mice, Tiam1 may be a potential target for the treatment of disorders involving memory impairments. SIGNIFICANCE STATEMENT The dentate gyrus (DG) is important for learning, memory, pattern separation, and spatial navigation, and its dysfunction is associated with neuropsychiatric disorders. However, the molecular mechanisms controlling DG formation and function remain elusive. By characterizing mice lacking the Rac-GEF Tiam1, we demonstrate that Tiam1 promotes the stabilization of DG granule cell dendritic arbors, spines, and synapses, whereas it restricts the survival of adult-born DG granule cells, which compete with mature granule cells for synaptic integration. Notably, mice lacking Tiam1 also exhibit enhanced contextual fear memory and context discrimination. These findings establish Tiam1 as an essential regulator of DG granule cell development, and identify it as a possible therapeutic target for memory enhancement., (Copyright © 2021 the authors.)

Estrogen replacement therapy (ERT) is one of the most challenging issues women and their physicians have to face. Clinical and epidemiological studies have provided conflicting data regarding the cardiovascular benefit versus risk in women using ERT. Although ERT may improve several risk factors of coronary heart disease such as favorable changes in lipid profile, an associated increased incidence of uterine and breast tumors has jeopardized the clinical use of ERT. We reported here that the phytoestrogen alpha-zearalanol is effective against atherosclerotic development without overt growth-promoting effects in the uterus compared to estrogen. These results suggest clinical potential of this phytoestrogen as a "safe estrogen" with less risk of tumorogenesis.