查看更多>>摘要：? 2022 The Author(s)The vast compositional space in cubic Cr23C6-type compounds (space group Fm3ˉm) opens up possibilities to tune properties by performing substitutions. In this study, the magnetic properties have been explored in a selected (Mn,Co)23B6-compound by the means of synchrotron X-ray diffraction, neutron powder diffraction, magnetometry and electronic structure calculations. Refinements of a structural model based on combined X-ray and neutron diffraction data revealed mixed metal occupancies at all metal positions. However, two sites were richer in Co and the other two showed an abundance of Mn. The magnetic characteristics showed a ferrimagnetic structure below 550 K, with the magnetic moments aligned along the crystallographic c-direction and the magnetic moments on corner atoms having an opposite direction compared to the rest, within the magnetic space group I4∕mm′m′. The total magnetic moments extracted from magnetometry and neutron diffraction data gave similar values at 6 K, 20.1 and 18.2 μB/f.u., respectively. Results from electronic structure calculations are in reasonable agreement with the experimental findings.
查看更多>>摘要：? 2022 Elsevier B.V.A series of Er3+-doped and Er3+-Yb3+ co-doped Gd2Zr2O7 phosphors were synthesized via hydrothermal method, and their multifunctional properties were studied in detail. The Raman spectra indicated that the products were the ordered pyrochlore phase of Gd2Zr2O7, which exhibited a good radiation resistance. The up-conversion (UC), down-conversion (DC) photoluminescence (PL) and X-ray excited luminescence (XEL) spectra of the Er3+: Gd2Zr2O7 samples showed the similar spectra profiles, which were composed of the prominent green (2H11/2/4S3/2→4I15/2) and weak red (4F9/2→4I15/2) emissions. The co-doping of Yb3+ ions was beneficial for the improvement in UC PL but led to the reductions in DC PL and XEL. Besides, the X-ray induced green emissions demonstrated a high-sensitivity to the dose rate and a long-term stability against the continuous X-ray irradiation. Moreover, using the fluorescence intensity ratio (FIR) technique, the temperature sensing behaviors were analyzed based on the thermally coupled levels (TCLs) 2H11/2 and 4S3/2 of Er3+. The FIRs were found to be insensitive to the excitation power variation, and the optimal relative sensing sensitivity reached ~1.1%K?1 at 298 K. These characteristics may enable the studied system applicable for optical thermometry, X-ray detection and X-ray imaging.
查看更多>>摘要：? 2022 Elsevier B.V.In present work, we investigated the martensitic transformations during loading/unloading cycles and stress-assisted cooling/heating cycles in TiNi-based single crystals and polycrystals with different microstructures. During loading/unloading cycles the formation of oriented B19′-martensite is only possible at stress levels higher than σcr(Ms0), so at low stress levels, below σcr(Ms0), the inelastic reversible strain, εtr, is not observed. In contrast, the inelastic reversible strain can be observed during cooling/heating cycles at low stress level σapp<σcr(Ms0). This means that the minimum stress level necessary for oriented martensite formation during cooling/heating cycles is lower than during loading/unloading cycles. An accommodating composition of both the oriented martensite variants and the thermal-induced self-accommodating martensite structure forms during stress-assisted cooling/heating cycles. On the contrary, during loading/unloading cycles the oriented martensite arises via MT from austenite or via the motion of twin boundaries in already-formed self-accommodating structure. It requires higher stress level, which is determined by high value of non-chemical energy ?GnonchA?M. Different processes occurring during loading/unloading cycles and stress-assisted cooling/heating cycles at low stress levels (σapp<σcr(Ms0)) results in different dependences Msσ(σapp) and σcr(Т) which do not coincide.
查看更多>>摘要：? 2022The standard solid state reaction method has been used to synthesize solid solution 0.8Bi1-xNdxFeO3–0.2PbTiO3 where x = 0.05, 0.10, 0.15 and 0.20 (BNFPT)x. The effect of Nd3+substitution on magnetic, ferroelectric, dielectric, and structural properties of 0.8BiFeO3-0.2PbTiO3 (BNFPT)x have been studied. The X-Ray Diffraction and Raman study of the samples revealed that the tetragonal structure with P4mm space group and rhombohedral structure with R3c space group exists simultaneously. The SEM study reveals uniform grain scattering. The 0.8BiFeO3-0.2PbTiO3 compound with Nd doping exhibits an increase in dielectric constant and reduce dielectric loss with respect to temperature and frequency. These features make the material as a promising candidate for the development of electronic device. At room temperature, all prepared samples exhibit weak ferro-magnetic behavior. However, a steady increase in residual magnetization was observed at 5 K. The magnetization result was found to be better than that of other rare earth doped BiFeO3-PbTiO3 solid solution. Ferroelectric study of the sample ascertained the pinning effect with low residual polarization in hysteresis loops. The reduction of leakage current with Nd doping is promising candidate for range of applications.
查看更多>>摘要：? 2022 Elsevier B.V.A facile acid vapor oxidation (AVO) method has been developed to grow highly round SnO2 nanospheres from 400 nm metal Sn thin films. This synthesis approach is able to directly grow nanostructures from a substrate in a simple reaction system involving the reaction of Sn film with the vapor generated from a hydrochloric acid solution in a Teflon-lined autoclave. A possible growth mechanism for the interesting SnO2 nanospheres has been proposed based on a series of time-dependent experiments. As-prepared SnO2 nanospheres have diameters around 150 nm. The influence of reacting time on the gas sensing properties of SnO2 was investigated by the detection of ethanol gas. The as-obtained SnO2 nanospheres are ultrasensitive to ethanol with a response of 1.49–50 ppb of ethanol at the low optimal working temperature of 170 ℃, which shows the promising candidates for high performance chemical sensors. This work offers a facile, shape-controlled, and efficient route to synthesize complex SnO2 nanospheres for gas detection with high performance, including ultrahigh sensitivity, good selectivity, and reversibility.
查看更多>>摘要：? 2022 Elsevier B.V.The phase and microstructure evolution of a precipitation-hardening high entropy alloy (HEA), Al0.5CoCrFeNi2Ti0.5, were studied. In order to promote the applications in surface modification, the proposed HEA was made into powders by using a gas-atomization process. The as-obtained powders presented a spherical shape with uniform element distribution; moreover, their phase constitution transferred from BCC to FCC-dominated structure while particle size varied from several to 120 μm. Further annealing treatments were conducted with the metastable fine powders to investigate the size effect in the microstructure. Below 500 °C, the structure kept a major BCC phase, but the size of grains arranged along (110) plane were getting smaller with temperature. FCC crystal became the dominant structure while the temperature was higher than 550 °C, and the transitional sigma phase existed at 700–800 °C. After annealed at 900 °C, the metastable fine Al0.5CoCrFeNi2Ti0.5 powders fully transferred to a stable structure composed of a dominant FCC plus minor BCC phases. Elemental mappings showed that the Al0.5CoCrFeNi2Ti0.5 HEA transformed from a microstructure with uniform element distribution to a coarsened system comprised of (Fe, Cr)-rich FCC matrix and (Al, Ti)-rich order BCC precipitate. Furthermore, the hardness of the Al0.5CoCrFeNi2Ti0.5 HEA increased by more than 20% on annealing treatment, from 5.50 ± 0.75–6.91 ± 1.49 GPa due to the solid solution and the precipitation strengthening effect brought about by Ti addition.
查看更多>>摘要：? 2022 Elsevier B.V.Designing and modulating the morphological structure of catalysts is of great significance to improve their catalytic activity and stability. In this work, PtRu alloy nanodendrites with tunable components were constructed by the introduction of Ru. Owing to the presence of electron transfer in the alloy nanocatalysts and their unique nanodendritic structures, Pt0.8Ru0.2 alloy nanocatalysts with optimal composition exhibited excellent electrocatalytic activity and stability in ethylene glycol oxidation reaction (EGOR) and methanol oxidation reaction (MOR). Among the nano-catalysts, mass activities of Pt0.8Ru0.2 nanodendritic catalysts to EGOR and MOR were 6.1 A mg?1 and 4.6 A mg?1, and the specific activities were 11.5 mA cm?2 and 8.68 mA cm?2, respectively, much better than those of commercial Pt/C catalysts. This work provides a strategy for designing efficient PtRu catalysts for fuel cells.
查看更多>>摘要：? 2022 Elsevier B.V.It is significantly important but remains challenging to prepare high performance microwave absorption materials in civil and military fields. Here, the Fe/Fe3C particles embedded in graphene-structured porous carbon (FGPC) served as a three-dimensional framework is prepared by simple carbothermal reduction, then vertical graphene nanosheets (VGSs) and Fe3O4 nanorods are successively grown on FGPC (FGPC/VGSs and FGPC/VGSs/Fe3O4) by thermal chemical vapor deposition, solution method, and subsequent heat treatment. As for comparison, VGSs and Fe3O4 nanorods grown on GPC without Fe/Fe3C particles (GPC/VGSs and GPC/VGSs/Fe3O4) are also prepared. The microwave absorption properties of them are investigated. Benefiting from the multi-component integration and well-designed structure, the FGPC/VGSs/Fe3O4 exhibits impressive microwave absorption performance with an optimal reflection loss of ?64.7 dB at 15.3 GHz, a matching thickness of 1.7 mm, filler loading of 12 wt%, and effective absorption bandwidth of over 4.8 GHz. This results from the balance of impedance match and attenuation capability. In detail, the introduction of magnetic particles and nanorods improves the impedance match. The multiple reflections and scatterings, moderate conductive loss and magnetic loss enhance the attenuation of microwaves. Thus, this work might open an avenue to design a highly efficient and lightweight multi-dimensional multiple component microwave absorbers.
查看更多>>摘要：? 2022 Elsevier B.V.We have grown Z-type hexaferrite Sr3Co2Fe23.04Al0.96O41 single crystal with a little Al3+ ion doping on the Fe3+ ion sites by the Na2CO3-Fe2O3 flux method. The magnetic properties and magnetoelectric (ME) coupling effects were investigated systematically. With Al3+ ion doping, the transverse conical magnetic phase could be maintained up to 359 K under small magnetic field (H). The magnetization increases with two steps to saturation at 300 K as shown in the M-H curve, implying the existence of a spiral spin order. The ME coupling effects occur near room temperture. Besides, the sign of the electric polarization (P) is independent of the H and the intensity of the electric polarization changes without any decays at 200 K under the oscillating magnetic field. Both of them are crucial for device application, such as information storage devices and non-volatile memory.
查看更多>>摘要：? 2022 Elsevier B.V.The hydrothermally-synthesized barium titanate (BaTiO3) nanofibers are mechanically milled and used to for the piezocatalytic RhB dye decomposition. It is found that the mechanical milling can improve the piezocatalytic performance of BaTiO3 nanofibers. With the increasing of the milling time from 0 to 120 min, the RhB dye decomposition ratio of BaTiO3 nanofibers first increases and then decreases. When the milling time is 30 min, for the 20 min vibration time, the RhB decomposition ratio of BaTiO3 is 94%, which is much higher than that (~65%) of the unmilled BaTiO3. On one hand, the enhancement in piezocatalysis of BaTiO3 may be originated from the exposure of active sites due to the increasement of the specific surface area after the mechanical milling. On the other hand, it is also found that the ferroelectric polarization strength of BaTiO3 nanofibers obviously increases after the mechanical milling, which is helpful to reduce the recombination of these positive and negative carriers in the catalytic process, resulting in the enhanced piezocatalysis performance. The mechanical milling provides a convenient, fast, and effective method for improving the piezocatalytic activity of BaTiO3 nanofibers.
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