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%).

All-dielectric terahertz metasurface for linearly-polarized multichannel transmission and superposition states of spherical and vortex waves

Compared to pure vortex waves,the superposition state of spherical waves and vortex waves has enough degrees of freedom to upgrade applications in particle manipulation,information encryption,and large-capacity communications.Here,we propose a new scheme to achieve superposition states and multichannel transmission of vortex and spherical waves.Two transmissive all-silicon metasurfaces that enable mutual interference between linearly polarized(LP)waves in the terahertz region are demonstrated.Type A can achieve interference between x and y polarized waves,while type B can achieve interference between x(or y)and x(or y)polarized waves.The multichannel transmission and superposition states of topological charges of+3,+2,and+4 are designed and demonstrated from theoretical,simulative,and experimental perspectives at 1.1 THz.In addition,the objective fact that the focused superposition state must be observed close to the focal plane is also revealed.The measured results are in good agreement with the theoretical and simulative results.This work provides an idea for the design of ultrathin terahertz devices and could be applied in the fields of information encryption and highfrequency communications.

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.

Strain-regulated sensing properties of α-Fe_(2)O_(3) nano-cylinders with atomic carbon layers for ethanol detection

The sensitivity of ethanol sensor is of paramount importance in a variety of areas,including chemical production with ethanol,alcohol testing for driving safety,etc.Herein,α-Fe_(2)O_(3) nano-cylinders with atomic carbon layers are synthesized,for the first time,through in-situ catalytic chemical vapor deposition combined with hydrothermal techniques for the detection of ethanol.The reported α-Fe_(2)O_(3)@C nano-cylinders with double surficial strain effects deliver an ethanol detection sensitivity of 8 times as compared with α-Fe_(2)O_(3) nano-cylinders,10 times higher as compared with its detection sensitivity to ammonia,para-xylene,methanol and benzene.The sensor also exhibits over-14-day operation stability and the minimum detection limit of 10 ppm.To our best knowledge,the performances surpass those of previously reported α-Fe_(2)O_(3).Such attractive performances are attributed to the enhanced charge transfer in α-Fe_(2)O_(3) owing to the double surficial strain effects of α-Fe_(2)O_(3)@C nano-cylinders and the efficient adsorption of ethanol with atomic carbon layers.

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.

High entropy dielectrics

High entropy oxides(HEO)are single-phase solid solutions which are formed by the incorporation of five or more elements into a cationic sublattice in equal or near-equal atomic proportions.Its unique structural features and the possibility of targeted access to certain functions have attracted great interest from researchers.In this review,we summarize the recent advances in the electronic field of high-entropy oxides.We emphasize the following three fundamental aspects of high-entropy oxides:(1)The conductivity mechanism of metal oxides;(2)the factors affecting the formation of single-phase oxides;and(3)the electrical properties and applications of high-entropy oxides.The purpose of this review is to provide new directions for designing and tailoring the functional properties of relevant electronic materials via a comprehensive overview of the literature on the field of high-entropy oxide electrical properties.

Enhanced microwave dielectric properties of wolframite structured Zn_(1-x)Cu_(x)WO_(4) ceramics with low sintering temperature

The crystal structure,Raman vibration,chemical bond characteristics,and microwave dielectric properties of Zn_(1-x)Cu_(x)WO_(4)(x=0-0.15)ceramics prepared by a solid-state reaction were investigated by XRD refinement,Raman spectroscopy,P-V-L theory and XPS.According to the P-V-L theory,the properties of the W-O bond are stronger than those of the Zn-O bond,which makes a major contribution to the dielectric properties.The relative permittivity is mainly affected by the average bond ionicity,and the variations in the dielectric loss and tf are mainly attributed to the lattice energy and bond energy.XPS shows that the presence of Cut could produce oxygen vacancy defects,increasing the dielectric loss.Additionally,Raman spectra show that the increasing molecular polarizability causes the Raman shift to move to a low wavenumber,and the changes in Raman intensity and FWHM lead to a decrease in the degree of short-range ordering.Particularly,Zn_(0.97)Cu_(0.03)WO_(4) ceramics sintered at 925℃ showed satisfactory properties(εr=14.20,tanδ=1.473×10^(-4) at 9.087 GHz,and tf=-40 ppm/℃),which can potentially be applied to LTCC technology and indicate that Cu substitution can not only reduce the sintering temperature,but also optimize the dielectric properties.