Papers by Author: Zhen Xing Yue

Abstract: The effect of CaO-B₂O₃-SiO₂ glass on the densification, microstructure and microwave dielectric properties of Ba₄Nd_9.33Ti₁₈O₅₄ ceramics was investigated in this work. It was found that the addition of a few amount of glass (≤2%) could effectively decrease the sintering temperature owing to the viscous sintering. However, locally porous structures were formed when overmuch glass was added because of enwrapped air bubbles and rapid grain growth. In addition, the amount of remaining glass after sintering could be decreased due to the re-crystallization of CaO-B₂O₃-SiO₂ glass. Sol-gel derived Ba₄Nd_9.33Ti₁₈O₅₄ ceramics containing 2 wt% glass can be well densified at 950°C and exhibit good microwave dielectric properties of ε_r=68 and Q×f=7400 GHz.

Abstract: The structural origin of imprint in Pb(Zr,Ti)O₃ (PZT) ferroelectric thin films derived by chemical solution deposition with Pt top and bottom electrodes was studied by in-situ high-resolution X-ray specular reflectivity of synchrotron radiation. Global structural parameters of density, thickness, and surface or interface roughness of each component layer in the thin film sample were obtained. No generation of interfacial layers with a different electron density from PZT and no interface roughening were observed at the interfaces of PZT and Pt during imprint. Thus, the results suggest that the imprint effect is more likely a bulk or electronic defects-related phenomenon.

Abstract: ZnNb2O6 ceramics with a columbite crystal structure, is a promising candidate for application in microwave devices. In this study, ZnNb2O6 nano-powders were prepared using Nb2O5 and Zn(NO3)2 as raw materials by Pechini method. The microstructure and crystal structure of ZnNb2O6 powders were investigated systematically using X-ray powder diffraction and SEM techniques. The effect of amount of citric and ethylene on the formation of sol-gel and the particle size of ZnNb2O6 powders were also investigated using orthogonal design. Finally, the optimum process parameters for synthesis ZnNb2O6 nano-powders were obtained in this study.

Abstract: The dielectric ceramics of CaTiSiO5-CaTiO3 with ZnO and B2O3 as additives were sintered at 950°C. Of the ceramics with a small quantity of 2ZnO-B2O3 as the additive, the density is nearly the same as the one reported, εr= 83 ~ 99, tgδ < 7×10-4, αε= (-100~+100) ppm/°C. The crystal phases and microstructures are analyzed by X-ray diffraction and scanning electron microscope. It is found that the sintered ceramics is of biphase, comprising monoclinic CaTiSiO5 and orthorhombic CaTiO3, and the grains are mostly the small circular ones, having diameters of 1~29m. By adjusting the composing of the ceramic, a high frequency dielectric ceramic CaTiSiO5-CaTiO3, of which αε= (-50~+50) ppm/°C was attained.

Abstract: Dense NiCuZn ferrites consisting of fine grains were prepared by spark plasma sintering (SPS) at 750°C for 3 min under a uniaxial pressure of 15 MPa. The powders were densified to >95% of theoretical density by the SPS process, and the average grain size of the prepared NiCuZn ferrite was < 1 /m. The saturation magnetization of prepared specimens (without further annealing treatment) was approximate 50.54 emu/g, which was slightly smaller than that of 52.21 emu/g for specimens prepared by conventional sintering at 980°C for 4 h. Phase identifications indicated that prepared NiCuZn ferrite existed impurity phase (Cu2O), and Cu2O would gradually transform to CuO when annealing temperature increased.

Abstract: xBST-(1-x)YIG composite ceramics with x=0~1 were prepared by solid-state reaction method. The variations for phase compositions were determined by XRD, and the magnetic and dielectric properties of the composites were studied in the frequency range of 100Hz~1GHz. The results showed that the composites (x=0.1~0.9) are consisted of BST phase and YIG phase and no significant chemical interaction occurs between these two phases. The composite materials exhibit excellent frequency dependences of dielectric and magnetic properties. The resonance frequency and high frequency characteristics of YIG are improved by additions of BST, and when x=0.3, xBST-(1-x)YIG has the best dielectric and magnetic properties.

Abstract: Cofiring behavior of composites consisting of ferroelectric PMZNT and ferromagnetic NiCuZn ferrite was investigated via X-ray diffractometer (XRD), thermomechanical analysis (TMA) and scanning electron microscopy (SEM). Mismatch of sintered camber consisting of two layered structure of ferroelectric PMZNT and NiCuZn ferrite was observed. Mismatched sintering behavior was modified by adopting PMZNT and NiCuZn powders to form composite materials. The temperature of appearance pyrochlore phase in prepared composite materials is lower than that of sintering pure PMZNT material. The grain size of PMZNT and NiCuZn in prepared composites is smaller than that of sintering pure PMZNT and NiCuZn ferrite, respectively.

Abstract: The plagioclase feldspar (NaxCa1-xAl2-xSi2+xO8, 0<x<0.67), has been synthesized under sub-solidus conditions using the solid-reaction technique. X-ray diffraction (XRD) was used to study the temperature dependency of the phase and structure transformations. Scanning electron microscopy (SEM) was performed to demonstrate the micro-structure of the sintered samples. The dielectric properties in microwave (MW) frequency region, including the dielectric constant, Qxf and the temperature coefficient were measured by the microwave network analyzer. The results revealed the value of Qxf decreases when 0≤x≤0.2, while increases when 0.2≤x≤0.67. The lowest value of Qxf was at x = 0.2.

Abstract: In this work hexagonal perovskite powders of CaLa4Ti4O15 were prepared by citrate sol-gel method. The calcined temperature was 1150oC, which is lower than that of the conventional solid method. Dense CLT ceramics were produced at sintering temperature of 1600oC. The crystal structures and microstructures were investigated by XRD, TEM and SEM, respectively. Compared with samples produced by solid method, the sol-gel derived CLT ceramics exhibited a near zero temperature coefficient of resonant frequency (τf ) of -6 ppm/oC, and other microwave properties , εr ~ 43, Q×f ~ 42000 GHz were also obtained. Moreover, the sintering temperature of the CLT ceramics could be reduced to 1400 oC by addition of B2O3-ZnO.

Abstract: In this paper, several kinds of synthesis techniques were adopted; not only conventional solidstate reaction method but also solution synthesis techniques, including co-precipitation and hydrothermal synthesis, in addition to the gel-casting for complex shape of ceramic components and tape-casting of large scale thin plate for microwave IC. Different kinds of microwave ceramics were prepared, such as materials with low permittivity and high quality factor, moderate permittivity and good quality factor, and, high permittivity and reasonable quality factor, in addition to near zero of temperature coefficient of resonance frequency. Series of microwave devices were developed, for examples, dielectric resonators, dielectric filters, GPS antennas, communication connectors, and thin substrates for microwave IC.