查看更多>>摘要：This work reports the preparation and properties of double-layered GeTe/Sb2Te heterostructures that exhibit remarkable improvement in thermoelectric performance compared to single layer systems. The double-layered (GeTe)80 nm/(Sb2Te)100 nm achieved a maximum power factor value of 413 mu W/mK2 at 500 K. Notably, by tuning layer thickness ratios, the reduction of transition temperatures and lowering in the resistance drift can be also achieved. Thermal heating of the amorphous heterostructures reveals intermixing between the layers, which results in the formation of GeSb2Te4 as the first phase and the crystallization of GeTe layer at higher temperatures. The crystallization process led to the increase in electrical conductivity of the heterostructures. Moreover, the newly formed GeSb2Te4/GeTe interfaces induce the strong energy barrier to block carriers, thus contributing to the increased Seebeck coefficient and power factor. Overall, this work shows a way to improve materials properties by using double-layered chalcogenide heterostructures.
查看更多>>摘要：We have developed a flexible method for calculating the grain boundary (GB) inclinations of voxelated grain structure data using smoothing algorithms. We compared the performance of four algorithms: the linear interpolation, Allen-Cahn, level-set, and vertex algorithms. We assessed their accuracy using 2D and 3D cases with known inclinations. The vertex algorithm provided the best balance between accuracy and efficiency for 2D structures while the linear interpolation algorithm provided the best balance for 3D structures. We compared the GB inclinations calculated using our smoothing method on a 3D high energy X-ray diffraction microscopy (HEDM) dataset to those determined by meshing the GBs. The two approaches determined similar GB plane distributions, though they varied significantly at triple junctions. Finally, the smoothing method was demonstrated for two sources of 3D voxelated grain structures: HEDM data and results from Monte Carlo Potts grain growth simulations.
查看更多>>摘要：This study creatively proposed a technique to effectively overcome the strength-ductility mismatch of the assintered titanium matrix composites by in-situ planting TiB nano-fibers and La2O3 nano-particles as ultra-fine networks into the composite powder. (TiB+La2O3)/Ti composites with excellent strength-ductility synergy were fabricated by hot pressing. The ultra-fine network eliminated the Widmanstatten microstructure and exerted a significantly fine-grain effect. Thus, the elongation of the as-sintered 1.2 vol.% (TiB+La2O3)/Ti composite was significantly improved from 2.2 to 10.8% compared with the matrix alloy, and the ultimate tensile strength was simultaneously enhanced to 1098.6 MPa. Meanwhile, the tensile strength of 2.4 vol.% (TiB+La2O3)/Ti reached 774.8 MPa at 600 degrees C, even superior to many wrought composites. The strength-ductility synergy effects were mainly attributed to the significant fine-grain effect and the synergistic effect between nanoreinforcements and soft matrix. This work opened up a new route for directly sintering nanoparticles reinforced titanium matrix composites components with promising comprehensive properties.
查看更多>>摘要：A recent paper entitled "High temperature stability and mechanical quality factor of donor-acceptor co-doped BaTiO3 piezoelectrics" (Song et al., Acta Materialia, 181(2019) 200-206) reported a surprisingly high electromechanical quality coefficient Q(m) similar to 2010 in their BaTiO3-based Pb-free piezoelectric materials. In this commentary we show that such high Q(m) value appears to arise from a mistaken adoption of resonance and anti-resonance frequencies, which is inconsistent with the IEEE standard for Q(m) measurement. By using a commercial PZT-8 sample with manufacturer-certified Q(m) value and electromechanical coupling coefficient kp value, we demonstrate that the calculation method used in the above paper can lead to an overestimation of Q(m) value by 82 times and underestimation of kp to 1/10 of its correct value.
查看更多>>摘要：A series of SnSe/carbon nanotubes (SnSe/CNTs) composites, with homogeneous distribution of CNTs, were fabricated by combining solution synthesis with fast sintering. Enabled by CNTs addition, both the electrical conductivity and power factor are improved significantly; the lattice thermal conductivity is suppressed due to strengthened phonon scattering. As a result, a maximum zT of 0.90 is obtained in the SnSe/CNTs composite with 0.20 wt.% CNTs, - 90% higher than that of SnSe. In addition, the composite with 0.35 wt.% CNTs exhibits a dramatically increased compressive strength of 135 MPa, representing an - 81% increase. This work offers a composite design strategy for synergistically improving both thermoelectric and mechanical properties of polycrystalline SnSe.
查看更多>>摘要：In this work, Mn-doped SiGe alloys with high Curie-temperature (T-C) ferromagnetism are synthesized via spark plasma sintering (SPS). The structural characterizations indicate that the Mn-doped samples are composed of strained Si0.25Ge0.75 crystals due to the incorporation of substitutional Mn dopants in the SiGe lattice. The magnetization characterizations and X-ray magnetic circular dichroism (XMCD) measurements show that the Mn-doped samples exhibit Mn concentration-dependent ferromagnetism up to room temperature, owing to the spin and orbit magnetic moment contribution from the substitutional Mn acceptors. Furthermore, the magneto transport measurements reveal anomalous Hall effect and complex magnetoresistance in the ferromagnetic Mn-doped samples. This study gives insight into the fabrication and magnetic properties of Mn-doped SiGe alloys prepared by SPS and may be useful for related spintronic applications.
查看更多>>摘要：The zone-melted Bi2Te3 based alloys with excellent near room temperature figure-of-merit have dominated the field of commercial thermoelectric materials for many years. However, the poor mechanical strength restricts their application on the hot emerging miniature TE devices. Herein, we adjust the Bi/Sb ratio of the nanotwins strengthened Te-deficient Bi0.4Sb1.6Te2.98 alloy, obtaining a mechanically robust p-type Bi2Te3 based alloy with a high peak zT of 1.33 at 150 degrees C and an eminent zT(ave) of 1.16 over 30 to 250 degrees C. Then, taking this alloy and Cu0.01Bi2Te2.7Se0.3 as the p-type and n-type legs respectively, a module possessing high conversion efficiency of similar to 4.8% at a temperature difference of 270 degrees C is fabricated, which paves an effective way to develop robust miniature (Bi, Sb)(2)Te-3-based TE devices.
查看更多>>摘要：This paper reports a machine learning approach for evaluating micromagnetic and microstructural parameters from demagnetization curves of FePt granular films for heat-assisted magnetic recording (HAMR) media. We developed a neural network to predict parameters of magnetic anisotropy and volume fractions of defects such as [200] misoriented grains, {111} twined variants, and disordered grains. The neural network was trained on a synthetic dataset of out-of-plane demagnetization curves that were simulated using the micromagnetic model constructed from actual nanostructure of a FePt-X HAMR medium. Predicted nanodefects agreed well with those estimated by synchrotron X-ray diffraction, and the demagnetization curve simulated with the predicted pa-rameters accurately reproduced the experimental one. This work paves the way for a high-throughput magne-tometry-based characterization of FePt granular media for its structural optimization toward higher areal density of HAMR.
查看更多>>摘要：Manufacturing austenitic stainless steels (ASSs) using additive manufacturing is of great interest for cryogenic applications. Here, the mechanical and microstructural responses of a 316L ASS built by laser powder bed fusion were revealed by performing in situ neutron diffraction tensile tests at the low-temperature range (from 373 to 10 K). The stacking fault energy almost linearly decreased from 29.2 +/- 3.1 mJm(- 2) at 373 K to 7.5 +/- 1.7 mJm(- 2 )at 10 K, with a slope of 0.06 mJm(- 2)K(-1), leading to the transition of the dominant deformation mechanism from strain-induced twinning to martensite formation. As a result, excellent combinations of strength and ductility were achieved at the low-temperature range.
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