Zircon ceramics have potential applications in next-generation wireless communication because of their low permittivity and adjustable temperature coefficient at microwave frequencies.However,the vast challenge of realizing ultralow dielectric loss still exists.Here,we propose a high-entropy strategy to enhance the bonding of the A-site dodecahedron in zircon and design(Nd0.2Eu0.2Y0.2Ho0.2Yb0.2)VO4 ceramics with a high quality factor(high Q×f,that is,low dielectric loss).The(Nd0.2Eu0.2Y0.2Ho0.2Yb0.2)VO4 high-entropy ceramics,which belong to the tetragonal zircon structure with the I41/amd space group,exhibit a low relative permittivity(εr=11.55),a negative temperature coefficient of resonant frequency(τf=−37.3 ppm/℃),and a high Q×f of 76,400 GHz(at 12.31 GHz).The high Q×f value can be attributed to the high chemical bond strength and structural stability.Furthermore,the relationship between the crystal structure and the microwave dielectric properties of(Nd0.2Eu0.2Y0.2Ho0.2Yb0.2)VO4 high-entropy ceramics was analyzed through high resolution transmission electron microscopy(HRTEM),Raman spectroscopy,far-infrared reflection spectroscopy,and chemical bond theory.This work provides an effective avenue for designing microwave dielectric materials with low loss to meet the demands of passive components.
Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.
WANG ZhixiangCHEN YingPANG QingyangLI XinWANG Genshui
High-entropy ceramics exhibit novel intrinsic properties.Hence,they have been explored for a wide range of applications ranging from thermal insulation and energy storage to advanced optical components.Recently,the semiconductor industry has faced a demand for higher-performance chips,necessitating higher aspect ratios in wafer fabrication and further miniaturization of linewidths.Therefore,novel materials with high plasma etching resistance and minimal contaminant generation are needed.The plasma-etching resistance displayed by high-entropy ceramics can be an innovative solution to this emerging challenge.In this study,we successfully fabricated single-phase high-entropy sesquioxide ceramics with high optical transparency,dense microstructure,and minimal residual pores.A structural analysis of the fabricated samples revealed a single-phase structure with excellent phase homogeneity.An evaluation of the plasma-etching resistance of high-entropy ceramics revealed for the first time a low etching rate of 8 nm/h compared with that of conventional plasma-resistant materials.These comprehensive characterizations of high-entropy ceramics indicate that they are promising candidates for significantly improving the production yield of semiconductors and for a wide range of potential applications,such as next-generation active optical ceramics.
Yu-Bin ShinSu Been HamHa-Neul KimMi-Ju KimJae-Woong KoJae-Wook LeeYoung-Jo ParkJung-Hyung KimHyo-Chang LeeYoung Hwa JungJung Woo LeeHo Jin Ma
Multiphase composition design is a strategy for optimizing the microstructures and properties of ceramic materials through mutual inhibition of grain growth, complementary property improvement, or even mutually reinforcing effects. More interesting phenomena can be expected if chemical interactions between the constituent phases exist. In this study, spark plasma sintering was used to prepare fully dense dual-phase (Zr,Hf,Ta)B2–(Zr,Hf,Ta)C ceramics from self-synthesized equimolar medium-entropy diboride and carbide powders. The obtained ceramics were composed of two distinct solid solution phases, the Zr-rich diboride phase and the Ta-rich carbide phase, indicating that metal element exchange occurred between the starting equimolar medium-entropy diboride and carbide phases during sintering. Owing to the mutual grain-boundary pinning effect, fine-grained dual-phase ceramics were obtained. The chemical driving force originating from metal element exchange during the sintering process is considered to promote the densification process of the ceramics. The metal element exchange between the medium-entropy diboride and carbide phases significantly increased the Young’s modulus of the dual-phase ceramics. The dual-phase medium-entropy 50 vol% (Zr,Hf,Ta)B2–50 vol% (Zr,Hf,Ta)C ceramics with the smallest grain size exhibited the highest hardness of 22.4±0.2 GPa. It is inferred that optimized comprehensive properties or performance of dual-phase high-entropy or medium-entropy ceramics of diborides and carbides can be achieved by adjusting both the volume content and the metal element composition of the corresponding starting powders of diborides and carbides.
Pai PengJi-Xuan LiuXiao-Ting XinWeichao BaoYongcheng LiangFangfang XuGuo-Jun Zhang
The sintering trajectory of the Ho,Pr:Y2O3 ceramics could be effectively adjusted by sintering in a flowing oxygen atmosphere instead of vacuum.The final-stage grain growth was significantly suppressed by the use of oxygen atmosphere presintering,resulting in smaller average grain sizes than those of samples sintered under vacuum,while the same relative density was achieved.After hot isostatic pressing(HIP),the oxygen presintered Ho,Pr:Y2O3 ceramics achieved excellent optical quality,with transmittance exceeding 80%at a wavelength of 680 nm.The codoping of Pr3+as deactivating ions effectively depopulated the lower energy level 5I7 during the Ho3+:5I6→5I7 transition,thereby making the Ho,Pr:Y2O3 ceramics more conducive to promoting population inversion in the 2.9μm laser wavelength range.
The development of advanced and efficient microwave-absorbing materials through the precise regulation of dielectric loss and impedance matching remains a significant challenge.In this study,(Hf0.25Zr0.25Ta0.25Nb0.25)C–SiC(HEC–SiC)biphasic ceramic powders were synthesized via a single-source-precursor route.The SiC content was systematically controlled by adjusting the amount of methyltrimethoxysilane.The resulting polymer-derived HEC–SiC composite exhibited a unique microstructure,with nanosized SiC particles uniformly distributed throughout the HEC matrix.As a result,the HEC–SiC-2 composite,containing approximately 21.21 wt%SiC,achieved a minimum reflection loss value(RLmin)of−54.28 dB at 12.39 GHz with a thickness of 3.14 mm.The superior microwave attenuation capability is attributed to optimized impedance matching,enhanced interfacial polarization between the HEC matrix and nanosized SiC,and dipole polarization induced by defects within HEC.This study offers a novel strategy for the fabrication of high-entropy ceramic–SiC biphasic composites with excellent microwave absorbing properties,paving the way for their application in electromagnetic interference shielding and stealth technologies.
Bin DuSaidi WangLinwei GuoYimin OuyangHanwei ChengYajuan ChengTao Zhang
