查看更多>>摘要：The Kurtz-Perry powder technique (KPPT) is widely utilized for the rapid characterization of newly grown nonlinear optical (NLO) materials available in pristine powder form. It assesses the effective nonlinear susceptibility of randomly oriented powder in comparison with a reference material. This technique becomes especially versatile when equipped with a broad wavelength range and intensity tunability because it provides key NLO properties of the materials under investigation, such as the frequency dispersion of the NLO susceptibility, phase-matching (PM) range, and laser-induced damage threshold (LIDT) as a guideline. In this study, wavelength-dependent NLO experiments (λ= 1100 - 3700 nm) were conducted on poly-crystalline LiInSe_2, prepared by high-temperature, solid-state synthesis. Our LiInSe_2 was found to be phase-matchable for λ > 2500 nm and the effective NLO susceptibility was estimated as 20.0 ± 1.9 pm/V, assessed at the static limit using commercial-grade single crystals of AgGaS_2 and AgGaSe_2 that were ground to powders. Alternatively, the effective NLO susceptibility was determined to be twice as large, ~40 pm/V, when utilizing a homemade, microcrystalline AgGaSe_2 reference at the static limit. This severe over-estimation of the NLO susceptibility that can occur while working with a homemade standard underscores the importance of using a commercial-grade reference with the KPPT. Furthermore, this study also discusses the LIDT of LiInSe_2 based on intensity-dependent SHG at 1064 nm with picosecond pulses, and compares with those of the commercial-grade AgGaS_2 and AgGaSe_2, determined under identical conditions. As defect levels can cause widely varying apparent color, thus optical bandgap, in LiInSe_2, this study stresses the importance of using a high-quality standard when exploiting the KPPT for NLO materials characterization. The role of defects is discussed in terms of Χ(2), phase matching onset and LIDT, parameters that predominantly affect the evaluation of new NLO materials.
查看更多>>摘要：To efciently establish the relationship among microstructure, composition and mechanical properties of the AlCoCrFeNi high entropy alloys, a high-throughput experimental method has been developed combining diffusion couple with the nanoindentation technique. In this paper, B2(A2) denotes that A2 (disordered bcc) particles are coherently dispersed in the B2 (ordered bcc) matrix, and vice versa for A2(B2). A B2(A2)-A2(B2)-fcc sandwich microstructure was produced by annealing an Al_(1.1)CoCrFeNi/CoCrFeNi diffusion couple. The following nanoindentation measurements found that the hardness of the A2(B2) structure is slightly lower than that of B2(A2), but the elastic modulus and ductility behave differently. The fcc region, on the other hand, has a larger ductility than both B2(A2) and A2(B2). In addition, the elastic modulus of fcc decreases with the increasing Al content, whereas the hardness does not signifcantly change with composition.
查看更多>>摘要：In this study, uncoated and copper-coated short carbon fber reinforced aluminum matrix composites were prepared by spark plasma sintering. The arrangement of the short carbon fbers was changed by hot rolling. The effect of copper-coating on microstructure evolution and properties was investigated. The results show that the copper-coating can inhibit the formation of harmful product Al_4C_3 at the interface and protect the structure of short carbon fbers from being damaged during hot rolling. Thus, the hot-rolled copper-coated composites have higher yield strength and better thermal conductivity. The interfacial product and its thickness affect the interfacial thermal resistance. For the interfacial product with low thermal conductivity, the thickness of the product is proportional to the interfacial thermal resistance. The dynamic re-crystallization mechanisms of uncoated and copper-coated composites include the continuous dynamic recrystallization mechanism, grain nucleation mechanism of the shear band, and the rotated-Gauss component promoting nucleation mechanism. The copper-coating enhances the interfacial coherence and promotes the nucleation and growth of P-oriented grains and rotated-Gauss-oriented grains by promoting the movement of shear bands.
查看更多>>摘要：? 2022 Elsevier B.V.Tin selenide (SnSe), a layered material with low thermal conductivity high thermoelectric properties, has recently attracted a lot of attention in the field of thermoelectrics. Herein, Sn1?xMnxSe is prepared by single-step hydrothermal route and the effect of Mn on the TE properties of SnSe compound were investigated. The formation of orthorhombic crystal structure is confirmed by X-ray diffraction (XRD) pattern. High crystalline nature of the sample and nanoparticles formation is observed in high resolution transmission electron microscopy (HRTEM). Thermal conductivity is obtained in the temperature range from 303 K to 653 K. The effect of Mn substitution leads to low thermal conductivity of 0.204 W/mK at 653 K, due to the shortened phonon lifetime through the various scattering mechanisms. This result demonstrates that the introduction of Mn substitution in SnSe can effectively lift the thermoelectric performance of polycrystalline SnSe via reduced thermal conductivity.
查看更多>>摘要：? 2022A number of recent reports indicate that SiCf-reinforced superalloy matrix composites show promise for increasing mechanical properties and lowering density. However, this has not yet been successfully demonstrated. The essence is the severe interfacial reaction. In present study, Ni, Fe, Co, Cr, Mo, 80Ni20Cr, 80Ni20Mo, 80Mo20Ni (in wt%), and Waspaloy-SiCf systems were fabricated. Interfacial reactions were analyzed by optical microscopy, field emission scanning electron microscopy and electron probe microanalysis. The results indicate that superalloy matrix elements Ni, Fe, and Co react violently with SiC, whereas strengthening elements Cr, and Mo, react mildly. Addition of other elements to form alloying systems including 80Ni20Cr, 80Ni20Mo, 80Mo20Ni and Waspaloy-SiCf fail to effectively suppress the severe reaction. Alloying could not suppress the reaction completely both in thermodynamic and kinetic. Matrix elements Ni, Fe, and Co dominate the reaction. Hence, the interface between superalloy and SiC fiber exhibits instability.
查看更多>>摘要：? 2022 Elsevier B.V.Lead-free 0.7BiFeO3-0.3BaTi1?xMnxO3 ceramics, where x ranges from 1% – 10%, were prepared by conventional solid state reaction method. Effect of addition of MnO2 on the structural, spectral, electrical, magnetic and piezoelectric properties of 0.7BiFeO3-0.3BaTiO3 material were studied systematically. The previous studies have emphasized on the doping in BiFeO3 rather than doping in BaTiO3 in BiFeO3-BaTiO3 system. Our work focuses on the influence of Mn doping in BaTiO3 in the BiFeO3-BaTiO3 system. All the ceramics were calcined at the optimum temperature of 800 °C to minimize the impurity phases to a great extent. The synthesized ceramics have a co-existence of R and T phases with a space group of R3c and P4mm respectively with a small amount of Bi25FeO40 impurity. The sample for x = 0.01 has R as the host phase rather than T phase, but as the concentration of Mn increases to 0.10, the R phase and T phase start forming a more stable solid solution. Additionally, the doping effect of Mn on grain and grain boundary was studied at 300 °C and illustrated by their equivalent circuits with the help of ZView 2 software. The grain resistance decreased significantly for the sample with x = 0.10. Hence, the addition of MnO2 significantly enhanced the electrical and piezoelectric properties of the 0.7BiFeO3-0.3BaTiO3 material. The improved electrical properties at high temperature and low frequencies εr =1.8 × 109, σ = 4.1 × 10?3 S cm?1 and piezoelectric property d33 = 128 pC/N was obtained for x = 0.10.
查看更多>>摘要：? 2022 Elsevier B.V.In order to improve the hydrogen storage capacity, Ti19Hf4V40Mn35Cr2 alloy was prepared with low-temperature heat treatment (973 K, 2 h/8 h/72 h, water quenching). Microstructure, hydrogen storage properties and hydrogen absorption/ desorption mechanism have been investigated. The results show that as-cast and heat treated Ti19Hf4V40Mn35Cr2 alloys consist of BCC phase, C14 Laves phase and Hf-rich phase. Large amounts of equiaxed dendrite BCC phase and eutectic structure (BCC phase + C14 Laves phase) were formed after heat treatment. The hydrogen storage capacity at the room temperature comes the highest up to 2.34 wt% for holding 72 h, which is 12% points higher than the as-cast alloy. The activation energy of as cast Ti19Hf4V40Mn35Cr2 alloy was about 83.30 kJ/mol, and the activation energies of heat treated alloys decreased to 66.26 kJ/mol, which is caused by the decreasing stability of hydride after heat treatment.
查看更多>>摘要：? 2022 Elsevier B.V.High refractive glasses in the La2O3–Nb2O5–B2O3 (LNB) system were synthesized by the melt-quenching technique and correlations between their compositions and structural features were clarified. It was found that the refraction index of the LNB glasses is tunable from 1.71 to 1.98 by the variation of the Nb2O5 fraction from 5 to 30 mol%. The infrared spectroscopy analysis implies on the presence of three and four coordinated borate units, as well as six coordinated niobium atoms. The X-ray absorption (La L3-edge and Nb K-edge XANES and EXAFS) spectroscopy and total X-ray scattering results show that niobium atoms maintain octahedral oxygen coordination despite the wide variation of the Nb2O5 content, while average lanthanum coordination number is versatile and changes from ~8 to ~10. The interatomic distance values testify that the niobium octahedra in the glass network are connected only “by corners”. The stability of niobium local atomic structure implies that the main source of the changes in the optical properties of studied glasses is the variation of the Nb2O5 content. The deeper understanding of the local atomic structure of the high refractive index LNB glasses paves ways for the development of new glass wafers for cutting-edge augmented reality devices.
查看更多>>摘要：? 2022 Elsevier B.V.Fe1?xKxSe0.5Te0.5 ( x = 0, 0.025, 0.05, 0.075 and 0.1) single crystals were grown by self-flux method. The effects of K-doping on the length of c-axis, critical temperature, anisotropy and critical current density were investigated. With the increase of K-doping content x, the length of c-axis increases, the critical temperature rises at first and then falls, and the anisotropy decreases. The critical current density displays a significant increase at x = 0.075. Subsequently, the superconducting properties of Fe0.925K0.075Se0.5Te0.5 were thoroughly studied. The field-dependent pinning energy U(H) and the temperature-dependent upper critical field Hc2(T) were given. Additionally, the Dew-Hughes model was used to scale the flux pinning force, and the result suggests that the superconductor had a temperature-induced pinning mechanism from normal point pinning to normal surface pinning, in which twins play an important role. We also discussed the temperature-dependent critical current density Jc(T)=Jc(0)(1-T/T1)n and found that the n-value depends on different flux pinning regimes, including single flux pinning, strong collective pinning associated with twins and weak collective pinning associated with point defects.
查看更多>>摘要：? 2022 Elsevier B.V.Self-supported nanoparticle electrocatalysts with multiple active sites and porosity have a bright prospect in the direction of oxygen evolution reaction (OER). In this work, a three-dimensional (3D) porous nanoparticle Fe-NiTe2/Ni2P is presented, which exhibits outstanding electrocatalytic activity and excellent stability. Specifically, the OER activity of Fe-NiTe2/Ni2P requires only 190 mV overpotential at the current density of 10 mA cm-2, which is the first time the overpotential of tellurides gets within 200 mV. It is because the rough porous 3D structure leads to a large number of exposed active sites, allowing enough channels to release oxygen and perform mass exchange. In addition, Fe doping can modulate the electronic structure of the catalyst, accelerate the electron transfer, and thus improve the activity of the catalyst. The catalyst remained stable in 1 M KOH solution for 22 h, indicating that it has strong corrosion resistance. In this work, a simple, efficient, low-cost and corrosion resistant iron-doped transition metal telluride electrocatalyst has been synthesized, which provides a valuable way for the study of water electrolysis.
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