查看更多>>摘要：Organic fluorescent dyes, as non-rare-earth phosphors, are crucial in the field of optoelectronic devices but significantly impeded by inherent strong aggregation-caused quenching effects and low thermal stability. To address these problems, herein, we devise a high-performance organic-inorganic composite phosphor consisting of ordered multilayer boron nitride (BN) nanosheets as a support that simultaneously improves the optical properties and thermal stability of acridine orange (AO). Besides, the emission intensities and colors of BN/AO composite phosphors can be adjusted by controlling AO concentrations and annealing temperature. In particular, the BN/AO composite phosphor displays strong yellow-green emission after 250 °C annealing. These findings offer a new avenue for the establishment of organic-inorganic hybrid luminescent materials.
查看更多>>摘要：Lead-free ferroelectric ceramics of (1-x)Ba0.98Li0.02TiO3-xBi(Mg1/2Sn1/2)O3 (abbreviated as (1-x)BLT-xBMS, x = 0, 0.02, 0.04, 0.05, 0.06, 0.08) were synthesized through conventional solid-state sintering method. The effects of Bi(Mg1/2Sn1/2)O3 addition on the phase transition, microstructure, the dielectric properties and the energy storage properties were investigated. All the BLT-BMS samples exhibited single phase perovskite structure. XRD and Roman spectrum confirmed the coexistence of the orthorhombic phase and tetragonal phase in the samples with x = 0.00–0.05, which turned to the coexistence of orthorhombic and cubic phase in the samples with x > 0.05. All the samples display dense microstructures with clear grain boundaries. The average grain size of the samples increases and the relaxor characteristics become stronger with the addition of BMS. The existence of orthorhombic phase apparently promotes the energy storage performance. The maximum energy density of 0.16 J/cm3 and the largest energy efficiency of 70.42% were achieved with orthorhombic/tetragonal ratio of 53/47 at x = 0.05.
查看更多>>摘要：Quaternary alloys CoMnCrAl, CoFeCrAl and their ternary counterpart Co2CrAl are studied experimentally and theoretically to explore the effects of the substitution of Mn or Fe atoms for part of Co atoms in Co2CrAl. It is found that CoMnCrAl or CoFeCrAl has a magnetization 0.92 μB/f.u. or 1.96 μB/f.u. respectively in agreement with the Slater–Pauling (SP) rule, different from the parent ternary alloy Co2CrAl whose magnetization significantly deviates. The combination of experimental and theoretical results suggests that the formation of Co-Cr antisite defect is suppressed by partially substituting Mn or Fe for Co. The main disorder defects in CoMnCrAl are Cr-Al and Mn-Cr antisites, Fe-Cr and Cr-Al antisites in CoMnCrAl. Since these antisite defects only have small effect on the minority band structure, the half metallicity of CoMnCrAl or CoFeCrAl is expected to have much better tolerance for atomic disorder, compared with Co2CrAl. A negative temperature coefficient of resistance for a long temperature range about 10–273 K has been found exclusively for CoMnCrAl compound. Quaternary alloy CoMnCrAl or CoFeCrAl is found to be compensated ferrimagnetism with a relative low magnetization but a Curie temperature (TC) significantly higher room temperature (RT), whose magnetization are relatively low, but TC higher than the ternary alloy Co2CrAl. Considering their low magnetization, decently high TC and the robust half metallicity, these two quaternary alloys may have important applications in spintronic devices.
查看更多>>摘要：The mechanical behavior and deformation mechanisms of a body-centered cubic (BCC) Ti29Zr24Nb23Hf24 (at%) high entropy alloy (HEA) was investigated in temperatures and strain rates from 700° to 1100 °C and 10?3 to 10 s?1, respectively. The HEA exhibits a substantial increase in yield stress with increasing strain rate. The strain rate sensitivity (SRS) coefficient is ~3 times that of BCC alloy Nb-1Zr and even ~3.5 times that of pure Nb. This high SRS is attributed to the high Peierls stress of the HEA, which is about twice the Peierls stress of pure Nb. On the other hand, the flow stress exhibits a tendency from strain softening to strain hardening with the increase of strain rate especially at the relatively low temperatures. This behavior is explained by a change in dislocation motion from climbing to multiple slip with the increase of strain rate. Taking the specimen subjected to 800 oC for example, dislocation walls formed at the early stage of deformation and at low strain rate of 10?3 s?1. In this case there is sufficient time to activate dislocations climb, which results in discontinuous dynamic recrystallization, and strain softening. However, when the strain rate amounts to 1 s?1, thermally activated processes such as dislocation climb are too sluggish. As a consequence, multiple slip systems are activated, and the dislocation interactions lead to the evolution of deformation bands, leading to strain hardening.
查看更多>>摘要：Since 2010, two-phase magnetoelectric (ME) films consisting of magnetostrictive and piezoelectric phases have been continuously developed with regard to their promising ME responses, for potential applications such as ultra-sensitive magnetic sensing, magnetic-field induced energy harvesting, and nano-transduction. Generally, one-dimensional piezoelectric nanowires, nanorods, and nanotubes are used to enlarge the active area for strain transfer between the piezoelectric and magnetostrictive phases of ME films. In this study, we developed 1–2 type individual nanotube-based ME films of CoFe2O4/BaTiO3 with main considerations in the optimization of magnetostrictive phase, piezoelectric phase, and interface between the phases, respectively. First, core-shell magnetostrictive nanoparticles were improved with a high resistivity of 3.89 MΩ·cm and saturation magnetization of 20.8 emu/g via a sufficient TiO2 coating on the CoFe2O4 nanoparticles. Then, individually free-standing TiOx nanotubes were prepared with an optimal structure exhibiting a large pore size of 220 nm and high interspace distance of 80 nm. Final 1–2 type ME films of CoFe2O4/BaTiO3 were successfully prepared by magnetostrictive particle electrodeposition and perovskite conversion in sequence. Enhanced dipole moments through high amounts of BaTiO3 phase were achieved with a maximal remnant polarization (Pr) of 0.192 μC/cm2 from the AC-electrodeposited (AC-) ME films exhibiting a dense film structure. Maximal ME coefficient of the AC-ME films was achieved with magnitude of 27.39 mV/cm?Oe at Hbias = 1000 Oe. As a result, considering the investigations, the 1–2 type ME films could be expected for possible applications such as high-sensitive magnetic sensors or low-power energy harvesters.
查看更多>>摘要：The development of novel transition metal carbides for improved hard coating technologies requires a detailed understanding of the factors influencing their stability and mechanical performance. To this end, we carried out first principles calculations based on density functional theory to tabulate the electronic structures, formation energies, and phonon dispersion curves of 3d transition metal carbides adopting zincblende, rocksalt, and cesium chloride structures. By analyzing the corresponding results, we outline a theoretical framework that describes how valence electron concentration and bonding configuration control the stability of these compounds. Many early transition metal carbides are predicted to be stable in the rocksalt and zincblende structures, enabled by filled bonding states, whereas the cesium chloride structure shows persistent instability. For compounds that are predicted to be stable, mechanical properties were investigated through calculation of elastic tensors, from which observable properties including Vicker's hardness and ductility were derived. A robust mechanical performance is shown to be correlated with complete filling of bonding orbitals as illustrated for rocksalt TiC and VC, which have calculated hardnesses of 25.66 and 22.63 GPa respectively. However, enhanced ductility and toughness can be achieved by allowing partial occupation of the antibonding states as in CrC, which has a relatively low Pugh's ratio of 0.51.
查看更多>>摘要：Prussian blue analogues (PBAs) have garnered much attentions in energy fields due to their three-dimensional open framework and electrochemical tunability. Noticeably, PBAs are also deemed extremely attractive as anode materials for batteries by virtue of their abundant internal active sites. However, their unclear redox mechanisms at lower potential severely restricts PBAs anodes to realize stable cycling performances. In this work, low-cost KxMn[Fe(CN)6]y□1?y·nH2O with diverse H2O content and structure are harvested via controlling the crystallization rate. It is firstly discovered that the KxMn[Fe(CN)6]y anodes undergoes multi-electron conversion reactions involving the fracture and recombination of Mn[sbnd]N bonds, while the stronger Fe[sbnd]C bond is preserved. Then, it is confirmed that weaker Mn[sbnd]N bond which need to be prepared at a faster crystallization rate is more conducive to the fast electrochemical kinetics of the reversible conversion paths. Accordingly, the K0.09Mn[Fe(CN)6]0.66□0.34·3.40 H2O with higher H2O content and weaker Mn[sbnd]N bond achieve the best Li-storage performances, exhibiting a reversible capacity of 480 mAh g?1 at a high current density of 1 A g?1 and considerable cycling stability exceeding 1000 cycles. The results also suggest that interstitial H2O could be beneficial for the better cycling stability of the KxMn[Fe(CN)6]y anodes. This work can provide new insights for the rational design of novel conversion anodes with high reversible capacity and superior cycling stability.
查看更多>>摘要：Gas sensors play a crucial part in air monitoring and exclusive detection of exhaled biomarkers. Co3O4 is regarded as a promising gas sensing material in lower temperatures (<200 °C) due to its affinity with oxygen and multivalent characteristics. However, its poor intrinsic conductivity leads to a lower response, hindering further practical applications. The introduction of Fe2O3 is desired to enhance the conductivity and regulate oxygen-vacancy defects. Thus, the Fe2O3@Co3O4 double-shelled nanotubes (DSNTs) for ethanol detection were successfully synthesized through a facile coaxial electrospinning route. The Fe2O3@Co3O4-1 DSNTs based sensor exhibited a lower detection limit (1 ppm) at 160 °C, and a remarkable response 3.5 times higher than that of pure Co3O4 HNTs. The sensor still maintained a good response even under a high humidity of 85%. An oxygen adsorption model combined with an energy band structure diagram was proposed to explain the enhanced sensing mechanism. The enhanced gas-sensing performance can be attributed to double-shelled hollow structures and heterojunctions, which promoted the active sites for gas adsorption on the surface of sensing layers.
查看更多>>摘要：In this paper, a modified top-down method is adopted to synthesize highly stable and water-soluble Molybdenum trioxide quantum dots (MoO3 QDs) without any surfactants. In this sonication induced modified method, commercial Molybdenum Oxide powder and Hydrochloric acid were used as the precursor and etchant, respectively. The impact of sonication bath temperature on the morphological, microstructural, size, crystal-structural, and optical properties of MoO3 QDs have been systematically investigated. The controlled sonication bath temperature during the synthesis process results in the tunability of the QDs. The mechanism behind the controlled size of the QDs deeply rooted in the acoustic cavitation phenomenon. The synthesized QDs exhibit poly-crystallinity with mixed phases: orthorhombic (α-MoO3) and hexagonal (h-MoO3). Interestingly, the complete elimination of the hexagonal phase from the QDs has been observed as a function of sonication bath temperature.
查看更多>>摘要：This paper describes the main results from an experimental investigation into tailoring the phase content and grain structure for high strength of a microstructurally flexible high entropy alloy (HEA), Fe42Mn28Co10Cr15Si5 (in at%), using rolling, friction stir processing (FSP), and compression. Optical microscopy, neutron diffraction, and electron backscatter diffraction were employed to characterize microstructure and texture evolution. The material upon rolling was found to have triplex structure consisting of metastable gamma austenite (γ), stable sigma (σ), and stable epsilon martensite (ε) phases. The adaptive phase stability exhibited by the selected HEA of very low stacking fault energy with strain, strain rate, and temperature was used along with grain refinement to enhance the strength. To this end, the complex structure was refined by FSP at 350 revolutions per minute (RPM) tool rotation rate, while increasing the fraction of γ and decreasing the σ and ε content. The strength was further enhanced by FSP at 150 RPM by further refinement of the grain structure and increasing the fraction of ε phase. The peak ultimate tensile strength of ~1850 MPa was achieved by double pass FSP (350 RPM followed by 150 RPM), the sequence which even more refined the microstructure and increased the fraction of σ phase. While the content of diffusion created σ phase remains constant during subsequent compression, the fraction of ε increases due to the diffusionless strain induced γ→ε phase transformation. The transformation facilitates plastic strain accommodation and rapid strain hardening, which has been attributed to the increase in highly dislocated ε phase fraction and transformation induced dynamic Hall-Petch-type barrier effect. Interestingly, a great deal of hardening ability was exhibited by the HEA even at very high strength. Roles of texture, grain size, and phase content on the transformation during compression have been rationalized and discussed in this paper.
NSTL
Elsevier