Papers by Author: Zhao Xian Xiong

Abstract: Rutile TiO₂ whisker/epoxy resin composites were prepared by hot-pressing process method. The effects of different content of TiO₂ whiskers on the microstructure, microwave dielectric properties and flexural strength for TiO₂/epoxy resin composites were investigated. Results show that flexural strength increased firstly, which can reach the maximum value (105.53 Mpa), then decreased with the content of TiO₂ whisker (v%) increase. Moreover, the dielectric constant and dielectric loss of the TiO₂/epoxy resin composites increase with the increased of TiO₂ whisker (v%). When the content of TiO₂ whisker is 60 v%, the TiO₂ whisker/epoxy resin composites exhibit a higher permittivity (ε_r = 10.74) and relatively low dielectric loss (tanθ= 0.021).

Abstract: 0.95MgTiO₃-0.05CaTiO₃ (95MCT) microwave dielectric ceramics was prepared solid-state reaction method. Effect of H₃BO₃ additive and forming pressure on sintering process, microstructure and microwave dielectric properties of 95MCT were investigated. The result showed that the additive of H₃BO₃ can lower the sintering temperature of 95MCT, and improve the densification of 95MCT. MgTi₂O₅ was found as mesosphere, which can be effectively suppressed through the additive of H₃BO_3. Excellent microwave dielectric properties of ceramics was obtained when the H₃BO₃ additive was 0.50wt%. The best value of dielectric constant (ε_r), quality factor (Q×f) and temperature coefficient of resonant frequency (τ_f ) of 21.54, 67,286GHz and-4.1ppm/^oC was obtained for the ceramics with sintering 1220^oC for 2h.

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: τMicrowave dielectric properties of 0.95MgTiO₃-0.05CaTiO₃ ceramics and their performances as H-shaped microstrip patch antenna were investigated. Best values of dielectric constant (ε_r) and quality factor (Q×f) of 19.00 and 66800GHz, respectively, were obtained for the microwave ceramics sintered at 1300°C for 3h. A near-zero temperature coefficient of resonant frequency (τ_f) of -4.7ppm/°C was obtained for the ceramics with sintering 1280°C for 3h. A new kind of H-shaped microstrip patch antenna with two resonant frequencies was fabricated by using of this kind of ceramics as antenna substrate. The return loss bandwidth of the patch antenna was extended with the increasing of substrate thickness at both resonant frequencies of the antennas, around 1.530GHz and 2.750GHz, respectively.

Abstract: Piezoelectric barium zirconate-titanate ceramic nanofibers were prepared by combination of Sol-Gel processing and electrospinning technique. The average diameter of barium zirconate-titanate ceramic nanofibers is nearly 200 nm. The x-ray diffraction pattern of the fibers showed that their crystalline structures displayed tetragonal perovskite structures. Interdigitated electrodes were sprayed on an epoxy resin substrate. BaTi_0.9Zr_0.1O₃ nanofibers were then aligned on the interdigitated electrodes and covered with the solution of epoxy resin, so as to obtain Piezoelectric Fiber/polymer Composites. The periodic output voltages with maximum value of 0.26V were obtained under harmonic excitation, by using a finger to apply a dynamic load on the top of the composites.

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: Practical evolutions of pores in BaTiO3 ceramics during sintering are studied, including the preparation of practical BaTiO3 ceramics and observation of ceramic microstructure by SEM. The reduction of porosity and thus dense process results from the change of the free energy in the ceramic system, which is altered by the disappearing of the interface between solid and pore. The sintering process are monitored, including sintering neck growth, pore shape and size changing, grain growth and compact body contracting. Theoretical formulae during the sintering process are applied for the computer simulation. The experimental results of BaTiO3 ceramics are in good agreement with that of simulation.