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Cu3N microcrystals were synthesized by a supercritical MeOH-NH3 technique with copper oxide and NH3 as copper and nitrogen source, respectively. The influence of reaction temperature on the fabrication of Cu3N particles was studied. The microstructures of products were characterized by XRD, SEM, FTIR, TG-DTA and XPS. Results show that product compositions depend greatly on the reaction temperatures and highly pure phase of Cu3N can be obtained at 250 °C. The as-prepared Cu3N displays a unique pyramidal morphology and the average edge length is 3–5 μm. Furthermore, the synthetic mechanism of Cu3N is also proposed. [ABSTRACT FROM AUTHOR]

Sn1−xMnxTe (x = 0, 0.09, 0.15, 0.20) bulk materials were prepared by melt spinning combined with spark plasma sintering process. Nanoscale grains were obtained, and the solid solubility of Mn was much enhanced by the ultrafast-cooling synthesis technique. The maximum of Seebeck coefficient and power factor are 242 µVK−1 and 19.97 µW cm−1K−2 at 873 K with the doping concentration of 15 at% Mn. A large amount of grain boundaries and doped atoms improve the scattering of heat-carrying phonons in a wide range of frequencies, and the scattering mechanisms are also explained by theoretical calculation. As a result, the minimum of lattice thermal conductivity is 0.66 µVK−1 at 873 K, the corresponding figure of merit is 1.26 for Sn0.85Mn0.15Te sample. This value is improved by 35% comparing with previously reported result. Our work indicates that melt spinning process is effective to develop SnTe related thermoelectric materials with excellent thermoelectric properties, which has the widespread commercial value and the prospects for development. [ABSTRACT FROM AUTHOR]

Un-doped single crystals of Mg2Si1−xSnx (x = 0.55, 0.65 and 0.75) were successfully prepared by high temperature gradient directional solidification (HGDS). In the Mg2Si0.45Sn0.55 crystal, Mg2Si precipitates were observed in the solidified microstructure, and no precipitates in the single crystals of Mg2Si0.35Sn0.65 and Mg2Si0.25Sn0.75. By measuring the electronic transport properties of these three single crystals, the Mg2Si0.35Sn0.65 has a largest PF value, about 2.5 times more than that of the nanocrystalline prepared by solid-state reaction methods. The corresponding ZT values of Mg2Si0.35Sn0.65 single crystal are greatly improved. It indicates that, the Mg2Si1−xSnx crystals prepared by HGDS can not only have a uniform microstructure, but also optimize the TE performance of the crystal. In addition, the first-principles calculation has been conducted to examine the intrinsic properties of Mg2Si1−xSnx single crystals, and the calculated data agree well with the experimental results. [ABSTRACT FROM AUTHOR]

A comprehensive analysis has been made of the n-type MgSiSn (0.25 ≤ x ≤ 0.75) compounds by the first principles calculation method. The calculated band structures in n-type MgSiSn show the conduction band convergence directly. This convergence in energy at x = 0.625 can enhance the Seebeck coefficient of the solid solution in comparison with other Sn contents. The Seebeck coefficient of MgSiSn could reach − 246 μV K at the optimal doping density of 3 × 10 cm. The enhancement of the Seebeck coefficient in the MgSiSn alloy results in a higher power factor of 6.2 mW m K at T = 550 K, and the predicted figure of merit is 1.53 at T = 700 K. Additionally, the ZT values can be maintained larger than 1.4 in a wide temperature range from 550 K to 800 K. [ABSTRACT FROM AUTHOR]

Un-doped Mg 2 Sn single crystal has been revealed to be anisotropic in Seebeck coefficient at different orientations and possesses orientation-dependent conduction sign reversal (OCSR). At room temperature, the [111] orientation of the crystal shows the n-type conduction with a Seececk coefficient value of −265μVK −1 and the p-type conduction behavior in the [ 1 1 ¯ 0 ] and [ 11 2 ¯ ] orientations with 148μVK −1 and 115μVK −1 , respectively. First principle calculation on the anisotropic Seebeck coefficient of the crystal matches well with the experimental results, showing that the conducting effective mass plays an important role in determining the value of Seebeck coefficient. The single crystal Mg 2 Sn with the preferred [111] orientation is expected to have the best thermoelectric performance due to its large Seebeck coefficient value and the same electrical and thermal conductivities compared with other orientations of the crystal. [ABSTRACT FROM AUTHOR]

Solid-state cooling based on elastocaloric effect possesses potential for refrigeration. The improvement of elastocaloric effect and thermal cycle stability is beneficial to enhance the refrigeration efficiency and service life of refrigeration equipment. Here, single-crystal Ni 50 Mn 31.6 Ti 18.4 shape-memory alloys were successfully prepared using directional solidification technique. The microstructure, martensitic transformation, isothermal stress-strain responses and elastocaloric effect of the single crystals with different solidification rates have been systematically studied. The single crystal solidified at 10 µm s−1 exhibits lower stress hysteresis Δ σ hy and much more superior adiabatic temperature |Δ T ad | than those of alloys solidified at 100 µm s−1 and 500 µm s−1, with the values of 34 MPa and 24.8 K. In addition, the single crystal at low solidification rate also performs excellent cyclic stability. All these results show that the single crystal with larger austenite primary dendrite arm spacing (PDAS) can effectively enhance the elastocaloric effect and thermal cycling stability in Ni 50 Mn 31.6 Ti 18.4 alloys. This work sheds a bright light on the relationship between the elastocaloric performance and microstructure for shape-memory alloys. • Single-crystal Ni 50 Mn 31.6 Ti 18.4 alloys were successfully prepared by directional solidification. • The alloy with large primary dendrite spacing has the excellent adiabatic temperature of 24.8 K. • Single-crystal prepared with larger primary dendrite spacing can effectively enhance the thermal cycling stability. [ABSTRACT FROM AUTHOR]

Phase selection under far-from-equilibrium condition has been investigated in three Cr 2 Nb-20/30/40Ti (at. %) alloys processed by laser surface melting (LSM) with scanning speeds of 50–200 mm/s. Phase identification was performed by micro-area XRD technique combined with SEM plus EDS methods. The results show that, at all scanning speeds of 50–200 mm/s, the microstructure of Cr 2 Nb-20Ti alloy consisted of single-phase Cr 2 Nb, whereas it evolved to monolithic β-Ti in the Cr 2 Nb-40Ti alloy. Meanwhile, the microstructure of Cr 2 Nb-30Ti alloy solidified with eutectic β-Ti/Cr 2 Nb at 50 mm/s, which transited to monolithic β-Ti as scanning speeds increased to 100–200 mm/s. Microstructures evolution was interpreted based on Trivedi-Magnin-Kurz (TMK) and Kurz-Giovanola-Trivedi (KGT) models incorporating the effect of non-equilibrium solidification. After the process of LSM, the micro-hardness of Cr 2 Nb-20Ti alloy was improved to a level of 9.0 GPa, and the fracture toughness was reduced to about 3.1 MPa m 1/2 ; while for the Cr 2 Nb-30/40Ti alloys, the micro-hardness decreased within a range of 5.5–6.6 GPa, but with a great increase of facture toughness of 21–23 MPa m 1/2 . [ABSTRACT FROM AUTHOR]

To improve the direct quantification of Carcinoembryonic Antigen (CEA) from body fluids by immunofluorescence, a surface acoustic wave (SAW) based biosensor was developed combined with an optimized silver nanostructure at the sensing region. Fluorescence signal amplification is achieved by patterning silver nanostructures using the rapid thermal annealing (RTA) method. In addition, the problem of background noise interference from nonspecific binding in human plasma is addressed by Rayleigh wave streaming at the immunoassay region, which shows a reduction in the limit of detection. The results show that the silver nanostructures significantly increase the sensor sensitivity by 49.99-fold and lower the limit of detection of CEA in phosphate buffered saline (PBS) solution to 101.94 pg/mL. The limit of detection of CEA biomarker in human plasma was successfully brought down to 11.81 ng/mL by reducing background noise using Rayleigh SAW streaming. This allows for a point-of-need sensor system to be realized in various clinical biosensing applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Al–40% Cu hypereutectic alloy samples were successfully directionally solidified at a growth rate of 10μm/s in different sizes (4mm, 1.8mm, and 0.45mm thickness in transverse section). Using the serial sectioning technique, the three-dimensional (3D) microstructures of the primary intermetallic Al2Cu phase of the alloy can be observed with various growth patterns, L-shape, E-shape, and regular rectangular shape with respect to growth orientations of the (110) and (310) plane. The L-shape and regular rectangular shape of Al2Cu phase are bounded by {110} facets. When the sample size was reduced from 4mm to 0.45mm, the solidified microstructures changed from multi-layer dendrites to single-layer dendrite along the growth direction, and then the orientation texture was at the plane (310). The growth mechanism for the regular faceted intermetallic Al2Cu at different sample sizes was interpreted by the oriented attachment mechanism (OA). The experimental results showed that the directionally solidified Al–40% Cu alloy sample in a much smaller size can achieve a well-aligned morphology with a specific growth texture. [Copyright &y& Elsevier]