Papers by Keyword: Hexagonal Perovskite

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: The Ba5(Nb1-xTax)4O15 (x=0~0.5) solid-solution ceramics with hexagonal perovskite structure were prepared by solid-state oxide route. The phases and structure of the sintered ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of composition and sintering temperature on the bulk density, microstructure and microwave dielectric properties were also investigated. As the value of x increased from 0 to 0.5, the Q×f value increases from 36,049 to 49,493 GHz (at ~9GHz), whereas the dielectric constant (εr) decreases from 39.21 to 33.03 and the temperature coefficient of resonant frequency (τf ) decreases from 78.6 to 19.4 ppm/oC. The results indicate that the microwave dielectric properties of Ba5(Nb1-xTax)4O15 ceramics can be easily modified in a large range by changing the relative content of Ta to Nb.