Papers by Author: Jing Pei

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: Microwave dielectric ceramics of CaO-2ZnO-xTiO2 (x=6~9) were prepared by citrate sol-gel method. The phase formation and structural properties of the ceramics were investigated as a function of titania content (x). Monophase of Ca2Zn4Ti16O38 polytitanates were formed at x = 8. With the increase of x, residual rutile phase were observed, whereas with the decrease of x, the CaTiO3 and Zn2TiO4 phases were detected. The microwave dielectric properties of the sintered ceramics were investigated using resonance method. The variation of dielectric properties of the ceramics as a function of titania content (x) was investigated. For the monophase of Ca2Zn4Ti16O38 polytitanate at x = 8, the dielectric properties showed minimum dielectric constant of 48.1, minimum temperature coefficient of resonant frequencies +44.1 ppm/oC, and maximum Q×f value of 31000 (at 6.921GHz). Deviating from x = 8, the dielectric constant and temperature coefficient of resonant frequencies slightly increased, and the Q×f value decreased. The variation was concerned with the presence of secondary phase.

Abstract: The nano-sized Ba(Zr0.2Ti0.8)O3 powder was prepared by citrate sol-gel method. The crystal structure and the particle size of the powder were characterized by XRD. The morphology of calcined powder and the sintered ceramics was observed by TEM and SEM, respectively. The particle size of the powders calcined at 600oC is about 10 nm. The dense ceramics can be obtained at sintering temperature of 1220 oC, which is much lower than that of the powder prepared by the conventional solid method. The effects of Al2O3 additive on the sintering behavior, microstructure and dielectric properties of Ba(Zr0.2Ti0.8)O3 ceramics were also investigated.