Papers by Author: Hong Qiu

Abstract: CaCu_{(3+ x)}Ti₄O₁₂ (x = 0, 0.001, 0.002, 0.004 and 0.008) ceramics with variation in copper micro-scale excess were prepared via solid-state reaction, Aqueous technology of tape casting was applied to obtain thick films of, about 100 μm in thickness. Crystal phases of the samples were identified by XRD. SEM of samples revealed that copper micro-scale excess can accelerate some important solid phase reactions in the sintering process, most because of liquid phase sintering mechanism. EDX analysis indicated that copper micro-scale excess could compensate for a lack of copper in sintering process. The Cu_3.004 sample exhibited the best dielectric properties with a very low dielectric loss (0.029), while retaining a very high dielectric constant (91,536), and the Cu_3.002 and Cu_3.004 samples exhibited a well frequency and temperature stability which was of significant industrial relevance. In this work, it was concluded that a certain amount of Cu micro-scale excess could improve dielectric properties, frequency stability and temperature stability of CCTO ceramics.

Abstract: Ceramics of (1-x)CaCu₃Ti₄O₁₂-xBi_2/3Cu₃Ti₄O₁₂, i.e., CCTO-BCTO, with x=0, 0.01, 0.1 and 0.25, respectively, were prepared via the conventional solid-state reaction. The phase structure of the ceramics was identified by X-ray diffraction. The microstructure of the sample was observed with scanning electron microscopy. Dielectric properties and impedance spectroscopy were measured using a LCR Meter, in which 0.9CCTO-0.1BCTO displayed highest dielectric constant (584108) and lowest dielectric loss (0.42) at 1kHz among the four kinds of specimens. Based on series of experimental results, an optimum amount of x was able to improve the dielectric properties of CCTO-BCTO, through adjusting the impedance characteristics of the grain and grain boundary.

Abstract: A new kind of gas sensors were prepared via chemical polymerization of polypyrrole (PPy) as sensitive layer on base of Mg₂SiO₄ porous ceramics. Thermal stability of the PPy sensitive layer was characterized with thermogravimetric analysis, including TG and DTA. Chemical structure of the samples was identified with X-ray diffraction (XRD) analysis. Microstructure of the PPy film was observed by a scanning electron microscope (SEM). Chemo-electrical relationship of the gas sensors was investigated with the resistance variation of PPy films at different gas concentrations. Based on series of experimental results, linear behavior of the chemo-electrical relationship was obtained for the gas sensor, y=0.00344x+1.33754, with R²=0.9734.

Abstract: A new type of porous ceramics, Mg2SiO4, for microwave application with low permittivity and high quality factors were prepared via gel-casting processing in this paper. Microstructure of the ceramics was observed and crystal structure of the samples was also identified. Moreover, emphasis was paid on the characterization of the microwave ceramics. Dielectric properties of the ceramics were measured by an automatic system of microwave measurement, resulting in dielectric constant of 3.51 and quality factor of 11,774 for the ceramic sample at frequency about 10GHz. Mechanical performance of the samples were also evaluated with maximal bending strength of 140MPa.

Abstract: PPy film with micro-antennal morphology was prepared by potentio-static method without any templates directly onto the surfaces of iron, platinum and gold-plated plastic sheets, respectively. Morphology of PPy film was observed with scanning electron microscopy, and its electrochemical properties were determined by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Attention was paid to the influence of reaction time, potential value, types of substrates, types and conconcentrations of electrolyte on the morphology and electrochemical properties of PPy film. Stable PPy film with thriftily long antennae was obtained on different substrates with good electrochemical properties. The film was applied for a prototype of biosensor, in which bioactive substance of glucose oxidase was immobilized.

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.

Abstract: Ba5(Nb1-xVx)4O15 (0≤x≤0.1) ceramics doped with H3BO3 were prepared by solid-state reaction. The effects of H3BO3 additives on the sinterability and microwave dielectric properties of the ceramics were investigated. The formation of a single phase was identified with the X-ray powder diffraction patterns of Ba5(Nb1-xVx)4O15 ceramics in the composition x from 0 to 0.025. Minor phases including Ba3(VO4)2 were formed as the secondary phase for the compositions with x>0.025. The dielectric constants (εr) of the ceramics increased firstly from 38.7 to 39.69 with x increasing from 0 to 0.01, and, then decreased to 36.91 with x=0.1, meanwhile, the unloaded quality factor and temperature coefficient of resonance frequency (τf) decreased as the x value increased from 0 to 0.1. Microwave dielectric properties, εr=36.91, Q×f =16,167GHz and τf =35ppm/°C, were obtained for Ba5(Nb0.9V0.1)4O15 ceramics with 1wt% H3BO3 sintered at 900°C for 2h.

Abstract: Degradation aging of BaTiO3 microwave ceramic capacitors for EMI applications at highvoltage, AC 10kV, was focused in this paper. Electric performances of the ceramic capacitors were systematically evaluated with thermal shock (5 cycles of –30 °C for 1 h and then 125°C for 1 h), damp heat (100% RH at 40°C for 500 h), and, endurance at high temperature (DC 10 kV at 100°C for 500 h). High reliability for the ceramic capacitor was obtained with optimal ceramic composition, sintering temperature, epoxy resin, curing agent and additives, which was satisfied with practical microwave technologies.