查看更多>>摘要：In order to obtain excellent thermoelectric property of PbTe at room temperature, the most effective ap-proach so far has been reducing the phonon thermal conductivity while maintaining the electronic per-formance. Based on the first-principles calculation, the scattering mechanisms of electrical transport and thermal transport are clarified. The electrical transport as well as thermal transport of PbTe under various mean free path are studied by taking into account electron/hole mean free path and phonon mean free path. The order of contribution to electrical transport is mean free path scattering > polar optical phonon scat-tering > acoustic deformation potential scattering > ionized impurity scattering. The Norma process dom-inates the three-phonon scattering channel, while the Umklapp process controls the four-phonon scattering channel. The 80% contribution of lattice thermal conductivity origins from acoustic branch, and the rest is from optical branch. When the hole/phonon mean free path is 10 nm, the ZT of p type is about 0.58, which is nearly four times larger than that of bulk ZT (0.15), implying the mean-free-path filtering is an effective method to enhance the value of ZT. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：This work is devoted to the study of the joint effect of SiO2 and PdOx on the SnO2 sensor properties when detecting CO in dry and humid air. Nanocrystalline SnO2 was obtained by wet chemical synthesis, modification with SiO2 was effectuated during hydrothermal treatment, modification with PdOx was carried out by impregnation method. All sensitive materials characterized by XRD, low-temperature nitrogen adsorption, HRTEM, TPR-H-2, XPS and IR spectroscopy. The sensor characteristics were studied when detecting CO in dry (RH = 1%) and humid (RH = 20%) air. Tin dioxide, jointly modified by SiO2 and PdOx, demonstrates the greatest sensitivity to CO in both dry and humid atmosphere. To explain the cooperative effect of PdOx and SiO2 in CO detection, the interaction of palladium modified samples with CO in dry and humid air was investigated by DRIFT spectroscopy in operando conditions. (C) 2021 Elsevier B.V. All rights reserved.
Kuzovnikov, Mikhail A.Antonov, Vladimir E.Hansen, ThomasIvanov, Alexandre S....
7页
查看更多>>摘要：It is currently known that three hydrides - PdHx, MoHx, and TiHx - exhibit an inverse isotope effect in superconductivity. Namely, the phase with a heavier hydrogen isotope, deuterium, has a higher critical temperature. Hydrides and deuterides of palladium have intensively been studied both experimentally and theoretically, but the origin of the isotope effect has not been established with certainty. The commonly accepted explanation is that the effect is likely to be due to the strong anharmonicity of the optical hy-drogen vibrations, which was considered to be responsible for the large deviation of the ratio of the fun-damental optical frequencies omega(H)/omega(D) = 1.51 from the harmonic value root 2 approximate to 1.41. In the present paper, powder samples of MoH1.1(1) and MoD1.07(3) were synthesized under a hydrogen/deuterium pressure of several gigapascals and studied by inelastic neutron scattering (INS) at ambient pressure and T = 10 K. The INS study demonstrated that optical vibrations of H atoms in MoH1.1 and D atoms in MoD1.07 are harmonic and the ratio of fundamental optical frequencies omega(H)/omega(D) = 1.44 is close to the harmonic value root 2 approximate to 1.41. This shows that anharmonicity is not a necessary condition for the presence of the inverse isotope effect. The MoD1.07 sample was additionally studied by neutron diffraction (ND) at ambient pressure and T = 100 K. In agree-ment with previous ND results for MoH1.2, the ND study of MoD1.07 showed that deuterium atoms occupied almost all octahedral interstitial sites in its hexagonal close-packed metal lattice and formed a NiAs-type crystal structure with the composition close to MoD. The overstoichiometric composition MoD1.07 of the deuteride is likely to result from a small fraction D/Mo similar to 0.07 of deuterium atoms partially occupying the tetrahedral interstices. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Conventional hydrides obtained thus far contain at least one type of metal with high hydrogen affinity, which can form metal hydrides near ambient pressure. In contrast, we synthesized metal hydrides comprising only metals with low hydrogenation affinity which are metals that do not form metal hydrides MHx (M stands for metal element, x > 0.5) below 1 GPa. This is because such hydrides are rare and would demonstrate novel properties and functionalities. To provide a guideline for synthesizing such hydrides, we clarified the hydrogenation reaction processes of FexMo1-x alloys at 6 GPa and 750 degrees C over a wide composition range of 0.41 <= x <= 0.88, where both Fe and Mo demonstrate low hydrogen affinities. Depending on the alloy composition, the hydrogenation reaction process can be classified into three types. Two kinds of novel hydrides were synthesized herein. First, FexMo1-xH (0.50 <= x <= 0.74) with metal elements at the vertices of hexagonal close-packed (hcp) lattices, and second, Fe0.88Mo0.12H with a complex crystal structure, which is likely to be a long-period close-packed structure. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：C70250 (Cu-2.6 wt%Ni-0.5 wt%Si) alloy plates with straight columnar grains, inclined columnar grains and equiaxed grains were produced by a heating-cooling combined mold (HCCM) horizontal continuous casting, respectively, and the influences of microstructure on the mechanical properties of the alloy were studied. The results showed that, when the casting speed was 30 mm/min, the straight columnar grains along the casting direction formed in the C70250 alloy plate and the precipitate content was relatively high, similar to 10%. When the casting speed was 50 mm/min and 80 mm/min, inclined columnar grains and equiaxed grains formed, respectively, with a low precipitate content of 6%. The high casting speed made the solid-liquid interface at the entrance of the cold mold and the solidified plate was cooled rapidly due to strong cooling effect, which suppressed formation of precipitated phase. The yield strength of the alloy plate with equiaxed grains were 219 MPa and the elongation to failure was 36%. For the plate with inclined columnar grains, its yield strength (76 MPa) were obviously lower than that of the other two plates and the elongation reached 45%. Compared with the equiaxed grain plate, the columnar grain plate had smaller grain orientation difference, better intergranular deformation compatibility and intergranular deformation uniformity, which was mainly responsible for its better plasticity. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：M-hexaferrite nanoceramics is of importance for advanced applications in which the dielectric response plays an essential role. Intrinsic dielectric response of M-hexaferrites related to its unusual crystal structure (ferrimagnetic unit cell contains two electric dipoles, switchable along the c-axis) is in homogeneous single crystals of quantum paraelectric type. The response becomes more complex when the hexagonal ferrites are functionalized by doping for various applications. We studied dielectric response of Sr0.95Nd0.05Fe12-xScxO19 (0 <= x <= 1.56) nanoceramics consisting of 50-100 nm thick single domain crystallites (for x >= 0.36). Ferric ions in oxygen octahedra substituted by Sc3+ change the collinear magnetism into a conical magnetic structure below the temperature of T-come and results in dielectric polarization of Dzyaloshinskii-Moriya type. The electric dipole of spin origin were found by us to contribute to the dielectric response (both free nanocrystallites and in form of pellets) of polar glass-like response below 250 K. Moreover, the scandium substituted expanded octahedron coupled to acoustic phonons may modify the electric dipoles at the nearest trigonal bipyramid. The modified electric dipoles may either interact with other dipoles or contribute to the dielectric response of Debye type relaxation. In the case of Nd3+ stabilized structure we found an additional dielectric relaxation (above 330 K) due to charge oxygen vacancies created to compensate the difference valence of Sr2+ and Nd3+. In the case of nanoceramics the dielectric response contains also the contribution from the heterogeneous ceramic structure and its microstructure. According to Maxwell Wagner - Koops model the high permittivity decreases with increasing frequency due to space charge polarization piled up at the poorly conducting grain boundaries. At higher frequencies impurity controlled electron hopping between the Fe4-Fe4 and Fe5-Fe5 Wyckoff positions is predominant. The third extrinsic contribution due to microstructure is related to size effect on magnetic conical structure resulting in a downward shift of glass transition anomaly. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this paper, tin doped indium oxide (ITO) films with high transparency and conductivity were fabricated on quartz by sol-gel method. The effect of four kinds of annealing atmospheres on the microstructure, morphology, surface chemical composition and optical-electrical properties has been investigated. Results show that the microstructure and morphology of the ITO films does not change much after heat treatment under different atmospheres. All annealed samples have the cubic bixbyite crystal structure of In2O3, with fine and uniformly distributed grains. The average grain size of each sample is approximately 10 nm. However, a noticeable dependence on the type of atmosphere is observed for oxygen vacancies and surface oxygen desorption. Different from oxidizing atmosphere, reducing or inert atmosphere is conducive to the formation of oxygen vacancies and desorption of adsorbed oxygen. Oxygen vacancies can effectively increase the carrier concentration of ITO. Oxygen desorption cannot only increase the carrier concentration, but also improve the carrier mobility. The issue for low conductivity of ITO nanocrystalline films can be solved by annealing in reducing atmosphere. This method can effectively control the grain growth and the chemical state of surface oxygen. The resistivity, average transmittance and Haacke FOM of the optimized ITO coated glass are 1.75 x 10-4 c cm, 88% and 0.0398 c-1, respectively. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Hydrophobic silane/graphene oxide (GO) composite coating implanted with BTAH inhibitor (BTAH-silane/ GO) was successfully fabricated on copper surface, and characterized using ATR-FTIR, Raman, EDS, XPS and EIS techniques. The results showed that GO was successfully covalently reacted with the silanol groups to form a Si-O-C band and BTAH inhibitor was uniformly embedded in the composite coating. The BTAHsilane/GO coated copper possessed the desirable high impedance modulus (Z(0.01 Hz)) of 5.7 M Omega cm(2) and high protection efficiency of 99.97%. The corrosion current density of the coated copper reduced over 3 orders of magnitude compared to its bare in 1 M neutral NaCl solution, and maintained over 99% even after 120 h immersion. In addition, the incorporated BTAH inhibitor exhibited the self-healing performance of BTAH-silane/GO coating in 1 M neutral NaCl solution. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In contrast to the disordered body-centered cubic (bcc) A2 phase, the ordered face-centered cubic (fcc) L1(2) phase exhibits negative magnetostriction (lambda) and has a high elastic modulus (E). Therefore, an in-depth understanding of the microstructural evolution of Fe-Ga thin films from bcc A2 phase to fcc L1(2) phase is essential to obtain Fe-Ga thin films with desirable properties. The transformation of the phase structure, magnetic domain structure, and magnetic properties of Fe72Ga28 thin films is analyzed in this study. The phase transformation of the Fe72Ga28 thin film from A2 to A2 L1(2) occurred after heat treatment, as determined by high-resolution transmission electron microscopy (HRTEM) and glancing-incidence X-ray diffraction (GI-XRD). Non-continuous lattice distortion at the phase boundaries of A2 and L1(2) was also observed, as shown by geometric phase analysis (GPA) and electron backscattered scattering detection (EBSD). Numerous edge dislocations at the phase boundaries were revealed by HRTEM. A shift in the magnetic domain structure from the maze-like domain to maze-like domain and honeycomb-like domain was detected by magnetic force microscopy (MFM). The variation in magnetic properties was determined to be related to the structural transformation and ununiform lattice distortion between the phase boundaries of the A2 and L1(2). (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：NiTi shape memory alloys are considered to be one of the fastest-growing materials with vast potential. However, the broader applications in intricately designed components are limited due to difficulties faced during welding processes such as degradation of functional and mechanical properties, precipitate formation, and selective vaporization of elements. In this study, the effect of laser power on precipitates formation and subsequent transformation temperatures on NiTi shape memory alloy was investigated by testing 0.8 kW, 1.0 kW and 1.2 kW welded specimens. The microstructures revealed the formation of Ni4Ti3 precipitates in the fusion zone and energy dispersive X-ray spectroscopy assessment exhibited preferential Ni evaporation. Differential scanning calorimetry analysis revealed the evolution of multiple step transformations (3-step/3-step) after laser welding. Furthermore, enthalpy change in peak transformations was evaluated and increasing order of enthalpy change was recorded for weld joints with increasing laser power. The kinetics of martensite transformation was evaluated by placing emphasis on average activation energy. High laser power welded joints showed easy martensitic transformation compared to low laser power welded joints. X-ray diffraction assessment also validated the existence of Ni4Ti3 precipitates and martensitic phase in NiTi alloy after laser welding. The electron backscattered diffraction maps of welded joints revealed the grain growth in the fusion zone and heat affected zone, and the unindexed black region emphasized the formation of distorted interphase of austenite/martensite and additional martensite phase at the fusion zone/heat affected zone interface. (C) 2021 Elsevier B.V. All rights reserved.
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