Multifunctional Integrated Organic-Inorganic-Metal Hybrid Aerogel for Excellent Thermal Insulation and Electromagnetic Shielding Performance

Vehicles operating in space need to withstand extreme thermal and electromagnetic environments in light of the burgeoning of space science and technology.It is imperatively desired to high insulation materials with lightweight and extensive mechanical properties.Herein,a boron-silica-tantalum ternary hybrid phenolic aerogel(BSiTa-PA)with exceptional thermal stability,extensive mechanical strength,low thermal conductivity(49.6 mW m^(-1)K^(-1)),and heightened ablative resistance is prepared by an expeditious method.After extremely thermal erosion,the obtained carbon aerogel demonstrates noteworthy electromagnetic interference(EMI)shielding performance with an efficiency of 31.6 dB,accompanied by notable loading property with specific modulus of 272.8 kN·m kg^(-1).This novel design concept has laid the foundation for the development of insulation materials in more complex extreme environments.

Magnetization reorientation induced by spin-orbit torque in YIG/Pt bilayers

In this work,we report the reorientation of magnetization by spin-orbit torque(SOT)in YIG/Pt bilayers.The SOT is investigated by measuring the spin Hall magnetoresistance(SMR),which is highly sensitive to the direction of magnetic moment of YIG.An external in-plane rotating magnetic field which is applied to the YIG/Pt bilayers,and the evolutions of SMR under different injected currents in the Pt layer,result in deviation of SMR curve from the standard shape.We conclude that the SOT caused by spin accumulation near the interface between YIG and Pt can effectively reorient the inplane magnetic moment of YIG.This discovery provides an effective way to modulate YIG magnetic moments by electrical methods.

Large positive magnetoresistance in photocarrier-doped potassium tantalites

We report on the high-field magnetotransport of KTaO_(3)single crystals,which are a promising candidate for study in the extreme quantum limit.By photocarrier doping with 360 nm light,we observe a significant positive,non-saturating,and linear magnetoresistance at low temperatures accompanied by a decreasing Hall coefficient.When cooling down to 10 K,the magnetoresistance value of KTaO_(3)(100)reaches~433%at a magnetic field of 12 T.Such behavior can be attributed to all the electrons occupying only the lowest Landau level in the extreme quantum limit.Light inhomogeneity may also contribute to large linear magnetoresistance.These results provide insights into novel magnetic devices based on complex materials and add a new family of materials with positive magnetoresistance.

Synthesis and fluorescence properties of CdTe:Eu3+ nanocrystals and core-shell SiO2-coated CdTe:Eu3+ nanospheres

Eu3+ doped-CdTe(CdTe:Eu3+)nanocrystals were prepared via a facile hydrothermal method,and Eu3+ was successfully incorporated into the crystal lattice of CdTe and measured by X-ray powder diffraction(XRD),transmission electron microscopy(TEM),ultraviolet-visible(UV-Vis) absorption spectroscopy and fluorescence emission.The CdTe:Eu^3+ nanocrystals still have a cubic crystal structure,and the corresponding XRD peaks of CdTe:Eu3+nanocrystals shift to larger angles compared with those of pure CdTe.The CdTe:Eu3+ nanocrystals are monodisperse and the particles size is about 2-4 nm.Compared with pure CdTe,the CdTe:Eu^3+ nanocrystals have larger band gap and thus exhibit blueshift in the emission spectra,which could be accounted for by the energy transfer between Eu^3+ and CdTe.To enhance the stability and functionality of CdTe:Eu3+nanocrystals,the CdTe:Eu3+nanocrystals were coated with SiO2 and the core-shell SiO2-coated CdTe:Eu3+nanocrystals(CdTe:Eu^3+@SiO2) were prepared via microemulsion method.TEM results show that CdTe:Eu3+nanocrystals are uniformly dispersed in the shell,and CdTe:Eu3+@SiO2 nanospheres are uniformly spherical with an average diameter of about 75 nm.The fluorescence emission of CdTe:Eu3+@SiO2(567 nm) shows a blueshift compared with that of CdTe:Eu^3+nanocrystals(632 nm),possibly because of altered surface properties after SiO2 coating.CdTe:Eu^3+and CdTe:Eu^3+@SiO2 with tunable photoluminescence are potentially useful in fabricating optical and bioimaging devices.

Solute redistribution and micromechanical properties of rapidly solidified multicomponent Ni-based alloys

The solute trapping effect and microhardness enhancement of quaternary Ni-5%Cu-5%Ag-5%Sn and quinary Ni-5%Cu-5%Ag-5%Sn-5%Ge alloys during rapid dendritic solidification are investigated by glass fluxing technique. In these two alloys, the experimental maximum undercoolings of 310 K(0.18 T_L) and 220 K(0.13 T_L) have been achieved and the rapidly solidified microstructures are composed of α(Ni) and(Ag) solid solution phases. The morphological transition from coarse dendrite into equiaxed structure is observed for α(Ni) phase with the increase of undercooling. The dendritic growth velocity of α(Ni) phase in quaternary Ni-5%Cu-5%Ag-5%Sn alloy is larger than that in quinary Ni-5%Cu-5%Ag-5%Sn-5%Ge alloy, which increases firstly and then decreases with the enhancement of bulk undercooling. The Vickers hardness of α(Ni) phase in these two alloys is enhanced with the increase of undercooling, which is attributed mainly to the grain refinement effect. Meanwhile, the solute trapping effect of Cu, Sn and Ge elements in the α(Ni) phase also contributes to the microhardness enhancement under large undercoolings. The addition of Ge element effectively increases the microhardness of α(Ni) phase due to solute strengthening mechanism.

Metastable liquid properties and rapid crystal growth of Ti-Ni-Al alloy investigated by electrostatic levitation and molecular dynamics simulation

Electrostatic levitation technique and molecular dynamics simulation were performed to investigate the thermophysical properties,liquid structure and crystal growth dependence on undercooling of Ti_(85)Ni_(10)Al_(5) alloy.The liquid Ti_(85)Ni_(10)Al_(5) alloy was substantially undercooled up to 335 K(0.18T_(L)).As undercooling increased,the potential energy of the liquid alloy decreased and the alloy entered into a high metastable state.At this state,the atoms tended to bond with each other and the clusters were inclined to convert into high-coordinated clusters,as confirmed by the fraction of the high-coordinated clusters variation.The enlarged clusters and enhanced local structure stability contributed to the increase of the thermophysical parameters and crystal growth velocity,and eventually dendrite refinement.The density,the specific heat and the surface tension of liquid alloy exhibited a linear relation with temperature and the shear viscosity of liquid alloy showed exponential variation which showed good agreement with the calculation results by molecular dynamics simulation.The growth velocity first increased slowly and then dramatically once the undercooling exceeded the threshold.The achieved maximum crystal growth velocity was 12.4 m s^(−1) and it was up to 326 times of the value at 94 K undercooling.

Effect of phase-separated patterns on the formation of core-shell structure

Revealing the mechanisms of self-organized core-shell(C-S)structure in immiscible systems has drawn considerable attentions,however,the further and fundamental understanding from the point of view of phase-separated pattern remains extremely rare.In this work,by realizing two phase-separated patterns in transparent immiscible system,namely nucleation-growth and spinodal decomposition,their effects on radius of minority-phase droplet(MPD)were examined,and subsequently the effect on C-S structure was further determined.It was found that compared with MPDs produced via nucleation-growth,the MPDs via spinodal decomposition are much larger and easier to form a C-S structure.This is mainly because the larger MPDs can migrate faster and are earlier to reach the sample’s center.In addition,two pathways of core formation were observed during the formation of C-S structure:one evolves from a ringlike structure in the phase separation of spinodal decomposition;the other derives from the collision of numerous MPD at sample’s center.Such a difference is ascribed to the combination of different growth kinetics and the volume fractions of MPD.These findings might provide an in-depth insight into the C-S structure formation in immiscible systems.

Highly efficient and broad electromagnetic wave absorbers tuned via topology-controllable metal-organic frameworks

Advanced electromagnetic(EM)wave absorbing materials with strong absorption and broad bandwidth are important for military stealth and elimination of microwave pollution in consumers’electronics.Metal organic framework(MOF)-derived metal/carbon hybrids with ordered structure are significantly urgent in this field.In this contribution,we presented a design strategy of hollow cage-like or solid box-like magnetic/dielectric Fe/Co/C and dielectric Fe/Mn/C EM wave absorbing nanomaterials via pyrolyzing Prussian blue’s analogs with controllable topology and phase composition.The solid box-like Fe/Co/C and hollow cage-like Fe/Mn/C showed favorable absorption property with a broad effective absorption bandwidth(EAB)and a low reflection loss(RL).Especially,the EAB of 8.8 GHz at a thickness of 2.5 mm for solid box-like Fe/Co/C nanocomplex prepared at 900℃is a new record for this type of materials.The design and tuning strategy for EM wave absorbers derived from topology-controllable MOF is important for EM functional materials possessing great potential in military stealth and consumers’electronics.

ZnO/nitrogen-doped carbon nanocomplex with controlled morphology for highly efficient electromagnetic wave absorption

In this work,zeolitic imidazolate framework-8(ZIF-8)with yolk-shell and hollow structures were pre-pared by a convenient chemical etching method.A subsequent pyrolysis of ZIF-8 enabled one to pro-duce ZnO/nitrogen-doped carbon nanocomplexes with original ZIF-8 morphology,where hollow struc-ture showed superior electromagnetic wave absorption capacity and was responsible for matching the impedance of free space.The minimum reflection coefficients of hollow ZnO/nitrogen-doped carbon nanocomplexes were-51.2 dB(700℃)and-52.4 dB(800℃),respectively,whereas the effective ab-sorption band width was as large as 4 GHz and the content of pyrolyzed hollow ZIF-8 was 15 wt%,which was inferior to the level among similar electromagnetic wave(EMW)absorption materials.The conve-nient and facile strategy paves the way toward designing hierarchical structures for highly efficient and light-weight electromagnetic wave absorbers.

Magnetic field-induced strategy for synergistic CI/Ti_(3)C_(2)T_(x)/PVDF multilayer structured composite films with excellent electromagnetic interference shielding performance

Lightweight,scalable,mechanically flexible conductive polymer composite was always desirable for electromagnetic interference(EMI)shielding applications.In this work,we showcased a novel approach to the superior EMI shielding composite materials by orchestrating the multilayered structure and synergistic system.The asymmetric structure with the carbonyl irons(CI)-rich Ti_(3)C_(2)T_(x)/poly(vinylidene fluoride)(PVDF)magneto-electric layer jointly behind the Ti_(3)C_(2)T_(x) nanosheets filled PVDF layer was designed and fabricated with the aid of a facile but efficient magnetic field-induced method and was then hotpressed into a multilayer structured film.Ti_(3)C_(2)T_(x) nanosheets were excluded by CI agglomeration layer in the asymmetric film to form the complete 3D electrical conductive skeletons.Based on this strategy,EMI shielding properties of the asymmetric multilayer structured composite was superior to the homogeneous blend and sandwiched or alternating layered composites.In addition,an increase in CI content in the composite referred to the thickening of CI-rich layers,making it gain the most powerful EMI SE values,i.e.42.8 d B for DCMP20–10 film(20 wt%CI,10 wt%Ti_(3)C_(2)T_(x))at a thickness of 0.4 mm.More importantly,the composite transformed from a reflection type to an absorption dominating EMI shielding material due to the multireflections and magneto-electric synergism in the CI-rich Ti_(3)C_(2)T_(x)/PVDF layers.Meanwhile,the EMI SE of the composites can be adjusted by increase of either theoverall thickness,or the layer numbers of m-DCMP sheets.The thickness specific EMI SE was calculated as 165.25 d B mm^(-1)for 4-sheet composite film,a record high value among the high efficiency polymer-based EMI shielding materials.This method offered an alternative protocol for preferential integration of excellent EMI shielding performance with high mechanical performance in CPC materials.

Hollow hydrangea-like nitrogen-doped NiO/Ni/carbon composites as lightweight and highly efficient electromagnetic wave absorbers

Hierarchical hollow-structured magnetic–dielectric materials are considered to be promising and competitive functional absorbers for microwave absorption(MA).Herein,a hierarchical hollow hydrangea multicomponent metal oxides/metal-carbon was designed and successfully produced via a facile self-assembly method and calcination process.Adequate magnetic NiO and Ni nanoparticles were suspended within the hollow hydrangea-like nitrogen-doped carbon matrix(HH N-NiO/Ni/C),constructing a unique hierarchical hollow structured multicomponent magnetic–dielectric MA composite.The annealing temperature and oxidation time were carefully regulated to investigate the complex permittivity and permeability.HH N-NiO/Ni/C delivers exceptional MA properties with maximum reflection loss of–45.8 dB at 1.7 mm thickness and displays a wide effective absorption frequency range of 5.6 GHz.The superior MA performance can be attributed to the following aspects:(1)The hierarchical hollow multicomponent structure offers plentiful of heterojunction interfaces triggering interfacial polarization;(2)nitrogen doped-carbon(N-C)facilitates the conductive loss by the unique electron migration path in the graphitized C and NiO/Ni;(3)magnetic NiO/Ni nanoparticles homogeneously dispersed within N-C form extensive C skeleton and strengthen the magnetic response ability;(4)hierarchical hollow wrinkled structures possess a large interspace and heterogeneous interface improving polarization loss and enhancing multireflection process and the unique structure satisfies magnetic and dielectric loss simultaneously resulting from synergistic effects of different components within the composites.