High sintering and dielectric performance:The improved(Mg,Zn)_(3)B_(2)O_(6) ceramics with the help of the DFT calculation

With the help of the first principle calculation,the solid-state reaction experiment was conducted to investigate the alteration in the sintering and the microwave dielectric properties of Mg_(3)B_(2)O_(6)ceramic with many Zn^(2+)substitutions.These properties were characterized using the scanning electron microscopy,network analyzer,X-ray diffraction,Raman spectroscopy,energy-dispersive spectroscopy,and thermomechanical and differential-thermal analyses.The coexistence of Mg_(3)B_(2)O_(6),Mg_(2)B_(2)O_(5)and ZnO ceramics could be observed with increasing Zn^(2+)addition,and the lattice distortion occurred in the Mg_(2)B_(2)O_(5)and Mg_(3)B_(2)O_(6)ceramics due to the substitution of Mg^(2+)with Zn^(2+).The electron density and the bond property of the MgO_(6)octahedron changed,and a quantitative method was used to discuss the variation in sintering,substitution and phase formation properties.The densification window was decreased to 1100℃,and the dielectric properties improved with the formation of a three-phase borate solid solution(dielectric constant=6.73,quality factor=112,000 GHz at 16 GHz(Q=7000),temperature coefficient of resonant frequency=-61.2 ppm℃^(-1),and relative density=97.0%).

Low-loss Cd-substituted Mg ferrites with matching impedance for high-frequency-range antennas

The effects of Cd^(2+) ions on the microstructure,magnetic properties,and dielectric properties of Bi_(2)O_(3)-added MgFe_(2)O_(4) ferrites(Cd_(x)Mg_(1-x)Fe_(2)O_(4),x=0.00,0.15,0.30 and 0.45)are obtained by adopting the solid-state reaction method at a low temperature(910℃).The objective is to achieve matching impedances,low magnetic and dielectric losses(tanδμand tanδε,respectively),and a relatively large miniaturization factor to reduce antenna size.Experimental results indicate that the cations occupying the tetrahedral(A)and octahedral(B)ion sites are redistributed,resulting in an enhanced super-exchange interaction between the two sublattices.As a result,improved magnetization,including the increase in saturation magnetization(41.74 emu/g)and decrease in coercivity(63.75 Oe),is realized.The real part of permeability(μ')also increases with increasing concentration of Cd^(2+) ions.When x is 0.15,matching impedances with equivalent μ'and ε'values are obtained over a long frequency range(1–150MHz).Moreover,the formation of a dense microstructure guarantees that losses occur at low orders of magnitude(tanδμ≈10−2 and tanδε≈10−3).Accordingly,these properties afford wide application perspectives for the proposed compounds in the high-frequency region,i.e.,from high-frequency to very-high-frequency bands.

Temperature dependence of spin pumping in YIG/NiO(x)/W multilayer

We report the temperature dependence of the spin pumping effect for Y_(3)Fe_(5)O_(12)(YIG,0.9μm)/NiO(tNiO)/W(6 nm)(tNiO=0 nm,1 nm,2 nm,and 10 nm)heterostructures.All samples exhibit a strong temperature-dependent inverse spin Hall effect(ISHE)signal I_(c)and sensitivity to the NiO layer thickness.We observe a dramatic decrease of I_(c)with inserting thin NiO layer between YIG and W layers indicating that the inserting of NiO layer significantly suppresses the spin transport from YIG to W.In contrast to the noticeable enhancement in YIG/NiO(tNiO≈1-2 nm)/Pt,the suppression of spin transport may be closely related to the specific interface-dependent spin scattering,spin memory loss,and spin conductance at the NiO/W interface.Besides,the I_(c)of YIG/Ni O/W exhibits a maximum near the TNof the AF NiO layer because the spins are transported dominantly by incoherent thermal magnons.

Relationship between structure and properties of microwave dielectric ceramic Li_((1+x))2MgTi3O8 based on Li non-stoichiometry

Li(_(1+x))2MgTi3O8(0.0≤x≤0.10)ceramics with Li non-stoichiometric ratios were prepared by the solidstate reaction method to inhibit the volatilization of Li.The effects of the Li non-stoichiometric ratios on the sintering behavior,crystal structure,microscopic morphology,Raman vibrations,electron density,and dielectric properties of Li(_(1+x))2MgTi3O8 ceramics were systematically investigated.The Li(1+0.06)_(2)MgTi_(3)O_(8)ceramics demonstrate the best dielectric properties withεr=26.33,Q×f=69435 GHz(@6.87 GHz,54%improvement),tf=2.95×10^(-6)℃^(-1).For the non-intrinsic factors,the high relative density(97.15%)and larger grain size(16.78 mm)allow the dielectric properties to be improved.As for the intrinsic factors,a reasonable excess of Li improves the bond ionicity of the MgdO bond,the lattice energy of the TidO bond,and the electron cloud density,thus optimizing the dielectric properties.Raman spectroscopy leads to the same result from the point of view of lattice vibrations.At the same time,the distortion of the polyhedra is also improved,so that tf also approaches 0.The improved Li(1+0.06)2MgTi3O8 has potential applications in microwave communication technology.

Molecular-beam epitaxy-grown HgCdTe infrared detector:Material physics, structure design, and device fabrication

Infrared(IR) detectors have important applications in numerous civil and military sectors. Hg Cd Te is one of the most important materials for IR detector manufacture. This review systematically discusses the progress of Hg Cd Te materials grown via molecular-beam epitaxy(MBE) for IR detection in terms of material physics, structure design, and fabrication. The material physics of Hg Cd Te includes crystal information, band structure, and electrical and optical properties. The characterization methods of the As-grown Hg Cd Te materials are also summarized. Then, four design structures of Hg Cd Te for IR detectors, with multilayer, superlattice, double-layer heterojunction, and barrier properties, which significantly improve the device performance,are discussed. The third section summarizes the studies on Hg Cd Te MBE-grown on different substrates, including Cd Zn Te, Si,and Ga Sb, in recent decades. This review discusses the factors influencing the growth of the Hg Cd Te film and their relationships and optimal conditions. Finally, we present the prospects and challenges associated with the fabrication and applications of Hg Cd Te materials for IR detectors.

Investigation of Antimony ions doping on crystal structure and enhanced microwave dielectric performance of MgTa_(2)O_(6)ceramics

Dielectric ceramics are promising in large-scale commercial millimeter-wave communication technology,such as 5G and the upcoming 6G,thanks to their excellent frequency selection characteristics and environmental stability.In this work,various contents of SbeO bonds were introduced into the MgTa_(2)O_(6)lattice using the solid-phase reaction method to investigate the effects on the lattice and microwave dielectric properties.XRD confirms that Sb ions successfully occupy Ta sites in the lattice and cause lattice shrinkage and crystallinity deterioration,which leads to a slight decrease in the quality factor.Furthermore,DFT calculations reveal that the doping leads to electron-biased aggregation toward O atoms,causing higher SbeO ionicity,but also attenuates the degree of ionization of Ta and Mg ions,which makes the dielectric constant of the doped samples vary non-monotonically with gradient doping.Satisfactorily,Sb doping substantially enhanced the thermal stability of the ceramics,with TCF values reduced from 36×10^(-6)℃^(-1)to 15×10^(-6)℃^(-1).

Design and application of active sites in g-C_(3)N_(4)-based photocatalysts

With the development in photocatalysis field,photocatalysts have received increasing attention due to their important role in environmental pollution and energy crisis.As a nonmetallic photocatalyst,graphitic carbon nitride(g-C3N4)has been widely recognized because of its excellent optical properties,low cost,and environment friendliness.In the g-C3N4 intrinsic frameworks,carbon atom tends to be the reducing active site,while nitrogen atom tends to be the oxidizing active site and reducing active site according to the difference of electronegativity.However,the quantity and quality of these active sites are affected by many factors,including C N covalent bonds,surface properties,etc.Active sites play an important role in photocatalysis;however,this role is not detailed in most reports.In this review,we proposed the following possible mechanisms of active sites in improving the photocatalytic activity of traditional g-C_(3)N_(4) based on its intrinsic:morphology regulation,carrier migration,surface active treatment,and substrate adsorption.The following factors affecting the active sites of g-C_(3)N_(4),including basal engineering and hybrid engineering,were also investigated.The roles of these active sites in improving the photocatalytic activity of g-C_(3)N_(4)-based photocatalytic materials,including morphology regulation,surface treatment,heteroatom doping,and interfacial interaction,were also expounded.Current challenges and future development of g-C_(3)N_(4)-based photocatalysts that are rich in active surface sites were also discussed.This review provides an in-depth understanding of g-C_(3)N_(4)-based photocatalysts.

自旋波逻辑门的关键器件研究进展

传统电荷型器件的发展已接近摩尔定律的极限,亟需寻求新原理或新架构进行信息处理,用"非电荷型器件"替代传统的"电荷型器件"是一种极具潜力的途径.其中利用电子自旋的集体进动所产生的自旋波进行信息的输运及计算,有可能成为后摩尔时代信息传输与处理的重要方式.自旋波逻辑器件在能量损耗、器件尺寸应用频段、逻辑实现等诸多方面具有传统器件无法比拟的优势.本文在介绍Mach-Zehnder干涉型自旋波逻辑门工作原理的基础上,从器件层面剖析自旋波逻辑门中的关键器件的实现原理,并系统性综述了这些关键器件近年来的研究进展.论文最后就自旋波逻辑门的未来发展做出了展望.

Low-temperature sintering and microwave dielectric properties of CaMg1−xLi2xSi2O6(x=0−0.3)ceramics

In this study, low-temperature fired CaMg1−xLi2xSi2O6 microwave dielectric ceramics were prepared via the traditional solid-state reaction method. In this process, 0.4 wt% Li2CO3-B2O3-SiO2-CaCO3-Al2O3 (LBSCA) glass was added as a sintering aid. The results showed that ceramics consisted of CaMgSi2O6 as the main phase. The second phases were CaSiO3 always existing and Li2SiO3 occurring at substitution content x > 0.05. Li+ substitution effectively lowered sintering temperature due to 0.4 wt% LBSCA and contributed to grain densification, and the most homogeneous morphology could be observed at x = 0.05. The effects of relative density, the second phase, and ionic polarizability on dielectric constant (εr) were investigated. The quality factor (Q × f) varied with packing fraction that concerned the second phase. Moreover, the temperature coefficient of the resonant frequency (τf) was influenced by MgO6 octahedral distortion and bond valence. Excellent dielectric properties of the CaMg1−xLi2xSi2O6 ceramic was exhibited at x = 0.05 with εr = 7.44, Q × f = 41,017 GHz (f = 15.1638 GHz), and τf = −59.3 ppm/°C when sintered at 900 °C. It had a good application prospect in the field of low-temperature co-fired ceramic (LTCC) substrate and devices.

Effect of Sb-site nonstoichiometry on the structure and microwave dielectric properties of Li_(3)Mg_(2)Sb_(1-x)O_(6) ceramics

The non-stoichiometric Li_(3)Mg_(2)Sb_(1-x)O_(6)(0.05≤x≤0.125)compounds have been prepared via the mixed oxide method.The influences of Sb nonstoichiometry on the sintering behavior,microstructure,phase composition along with microwave dielectric performances for Li_(3)Mg_(2)Sb_(1-x)O_(6) ceramics were studied.Combined with X-ray diffraction(XRD)and Raman spectra,it was confirmed that phase composition could not be affected by the Sb nonstoichiometry and almost pure phase Li_(3)Mg_(2)SbO_(6) was formed in all compositions.Appropriate Sb-deficiency in Li_(3)Mg_(2)SbO_(6) not only lowered its sintering temperature but also remarkably improved its Q×f value.In particular,non-stoichiometric Li_(3)Mg_(2)Sb_(0.9)O_(6) ceramics sintered at 1250℃/5 h owned seldom low dielectric constant ε_(r)=10.8,near-zero resonant frequency temperature coefficient τ_(f)=-8.0 ppm/℃,and high quality factor Q×f=86,300 GHz(at 10.4 GHz).This study provides an alternative approach to ameliorate its dielectric performances for Li_(3)Mg_(2)SbO_(6)-based compounds through defect-engineering.

Effects of W^(6+) substitution on the microwave dielectric properties of Ce_(2)Zr_(3)(MoO_(4))_(9) ceramics

Low temperature sintered Ce_(2)Zr_(3)(Mo_(0.9)W_(0.1)O_(4))_(9)(marked as CZMW)ceramics were synthesized via the conventional solid-state reaction method.X-ray diffraction results showed that the CZMW ceramics belonged to a Trigonal system with R-3C space group,and without any impure phase formation.The experimental facts revealed that the density and grain morphology greatly affected the microwave dielectric properties.The samples sintered at 825℃ exhibited good microwave dielectric properties.ε_(r)=9.85,Q×f=22,980 GHz(at 11.3 GHz)and a satisfactoryT_(f)(-1.5 ppm/℃)value.It is suggested that the CZMW ceramics are suitable for low-temperature co-fired ceramic(LTCC)applications in microwave devices.

Amelioration of sintering and multi-frequency dielectric properties of Mg_(3)B_(2)O_(6):A mechanism study of nickel substitution using DFT calculation

With the support of density functional theory(DFT)calculation,the amelioration of sintering and dielectric properties of the Mg_(3)B_(2)O_(6)(MBO)ceramic was realized through the substitution of magnesium with nickel.The TE-mode cylindrical cavity method was used to measure the dielectric properties at different frequencies.The thermo-mechanical analysis and simultaneous thermal analysis were used to characterize the chemical and mechanical properties.The phase composition was determined through the X-ray diffraction(XRD)and Raman spectrum.The microstructure was investigated using the scanning electron microscopy(SEM).Magnesium substitution with nickel(4 mol%)could ionize the B-0 bond of BO3,modify the vibration mode,improve the order degree,densify the microstmcture,decrease the intrinsic densification temperature,and ameliorate the dielectric properties of the MBO ceramics.The maximum values were achieved for the ceramics with 4 mol%nickel and sintered at 1175℃,that is,97.2%for relative density,72,600 GHz(10 GHz),75,600 GHz(11.4 GHz),and 92,200 GHz(15 GHz)for Q×f,7.1(10 GHz),7.01(11.4 GHz),and 6.91(15 GHz)for£r,and-56.3 ppm/℃ for if.

Enhanced performance of a fast GaAs-based terahertz modulator via surface passivation

Surface-modified semiconductors show enormous potential for opto-terahertz(THz)spatial modulation due to their enhanced modulation depth(MD)along with their inherent broad bandwidth.Taking full advantage of the surface modification,a performance-enhanced,all-optical,fast switchable THz modulator was achieved here based on the surface-passivated Ga As wafer.With a decreased surface recombination rate and prolonged carrier lifetime induced by passivation,S-passivated Ga As was demonstrated as a viable candidate to enhance THz modulation performance in MD,especially at low photodoping levels.Despite a degraded modulation rate owing to the longer carrier lifetime,this passivated Ga As modulator simultaneously realizes a fast modulation at a 69-MHz speed and as high an MD as ~94% in a spectral wideband of 0.2-1.2 THz.The results demonstrated a new strategy to alleviate the tradeoff between high MD and speed in contrast to bare surfaces or heterogeneous films/unusual geometry on semiconductors including Si,Ge,and GaAs.

Synthesis of yttrium iron garnet/bismuth quantum dot heterostructures with localized plasmon enhanced magneto-optical performance

Interactions between light and magnetic matter attracted great attention lately due to their potential applications in nanophotonics,spintronics,and high-accuracy sensing.Here,we grew bismuth quantum dots(Bi–QDs)with strong spin–orbit coupling on a magnetic insulator yttrium iron garnet(YIG)via molecular beam epitaxy.The YIG/Bi–QDs material shows an enhanced magneto-optical Kerr rotation up to 130%compared with that of a bare YIG film.The Bi–QDs were also introduced onto a lutetium–bismuth co-doped YIG film to form a hybrid system with remarkably enhanced Kerr rotation(from 1626 to 2341 mdeg).Ferromagnetic resonance measurements showed an increased effective magnetization as well as interfacial spin–orbit field in the YIG/Bi–QD heterostructures.Localized plasmons were mapped using electron energy loss spectroscopy with high spatial resolution,revealing enhanced plasmon intensity at both the Bi–QD surface and YIG/Bi–QD interface.Introducing Bi-QDs onto the YIG film enhanced Kerr rotation owing to the attenuated optical reflection and increased effective magnetization.The Bi–QDenhanced magneto-optical effect enables development of efficient nanoscale light switching,spintronics,and even plasmonic nano-antennas.

Bond, vibration and microwave dielectric characteristics of Zn_(1- x)(Li_(0.5)Bi_(0.5))_(x)WO_(4) ceramics with low temperature sintering

The bond,vibration and microwave dielectric characteristics of Zn_(1- x)(Li_(0.5)Bi_(0.5))_(x)WO_(4)(x=0-0.12)ce-ramics were investigated by XRD refinement,Raman and FT-IR spectroscopy and complex bond valence theory.The results showed that proper substitution of(Li_(0.5)Bi_(0.5))2þcan improve the sintering charac-teristics and microwave dielectric properties of ZnWO_(4).The increase of Q×f value was mainly attributed to dense and uniform microstructure,and the subsequent decrease resulted from the deterioration of structural stability and relative density.According to the complex bond valence theory,the chemical bond characteristics of ZnWO_(4) and Bi_(2)WO_(6) played an important role in the dielectric properties of the samples.Additionally,the samples(x=0.02)sintered at 900℃ showed satisfactory properties:ε_(r)=15.332,Q×f=35,762 GHz,and t_(f)=-65 ppm/℃,making it a potential candidate material for LTCC applications.